No~Shock~Zone

RV Electrical Safety: Surge Strips

Mike Sokol — Sun, 17 Apr 2011 15:48:15 +0000

This series of articles is provided as a helpful educational assist in your RV travels, and is not intended to have you circumvent an electrician. The author and the HOW-TO Sound Workshops will not be held liable or responsible for any injury resulting from reader error or misuse of the information contained in these articles. If you feel you have a dangerous electrical condition in your RV or at a campground, make sure to contact a qualified, licensed electrician.

This article was prompted by an RVtravel.com reader who wrote asking if it made sense to spend $300 on a surge protector for her RV.

Surge is one of those words that have fallen into fairly common usage when in fact; it’s not very descriptive of the situation. And interestingly “surge strips” do nothing to stop a long-term voltage “surge.”

So let’s start with a basic definition of voltage and the types of situations that can ruin your electrical gear. To gain a better understand of what we’re going to discuss, re-read my NSZ article HERE about voltage. As you will see, voltage is really electrical pressure, much like the water pressure in your pipes feeding the kitchen sink.

Electrical voltage (pressure) needs to be near a certain amount for electrical gear (like your computer) to be happy. And the voltage (pressure) we use in the USA is rated at 120 volts, give or take 5% according to the National Electrical Code. That means it could vary from a low of 114 volts to a high of 126 volts, and still be strictly within code. From a realistic standpoint though, it’s more likely to be as much as 8% low, so a 110-volt measurement is pretty common.

ELECTRICAL APPLIANCES are generally designed to run perfectly fine on anything from 105 volts to 130 volts or so. And 99.9% of the time that’s what you’re feeding them from the power line. But you can have under-voltage (brownouts) or over-voltage (broken neutral) conditions at a campground where this sustained voltage can go below 90 volts or above 150 volts. These are not voltage “surges,” so a so-called surge strip will do nothing to stop them from getting into your coach. But more on that later…

However, there are voltage “spikes” that can be induced on a power line from a variety of causes, the most dramatic one being a lighting strike near your area. That can cause a voltage “spike” of many hundreds or even thousands of volts to appear on your 120-volt wiring. Fortunately, that “spike” only lasts for a tiny fraction of a second (milliseconds) so it’s pretty easy to get rid of with a simple MOV device (Metal Oxide Varistor) built into a common “surge” strip which shorts these high-voltage spikes harmlessly to ground.

But MOV devices (which looks like a nickel with wires attached to both sides) are sacrificial elements. That is, just like a boxer in the ring, all “hits” are accumulated and they’ll eventually wear out and stop protecting your circuits from damage. Better “surge strips” have an indicator light to tell you if their MOV is still functioning or if it’s time to get a new surge strip. These MOVs are not field replaceable unless you have a soldering iron and a meter, so don’t try to fix one yourself.

The other common cause of voltage spikes are big motors being turned off, which then induces a reverse voltage spike of 10 to 100 times the nominal voltage. Again, these are short duration spikes of only a few milliseconds (1/1000 of a second) so a MOV protected “surge strip” will do a good job of shunting this voltage to ground without harm. I think the most common cause of this type of spike would be a big water pump at a campground when it switches off.

However, there’s an even bigger electrical boogieman at campgrounds that many RVers are unaware of. And that’s sustained over and under voltage conditions. This is where the voltage going into your coach from the power pedestal can dip very low (say, below 90 volts) or swing very high (180 volts or more) depending on the condition.

The low voltage condition is hard on appliances that need serious start-up current (like air conditioners) while the high-voltage condition is hard on electronics (like your computer, microwave electronics, and most everything else you plug in). And there have been instances where entire campground areas have been miswired with 208 volts instead of 120 volts. And certainly, a broken neutral connection in your 120/240-volt shore power plug can let the one side of your power dip to 60 volts while the other side rises to 180 volts with predictable disaster. In that case, the MOV in your surge strip will think that nothing is wrong and happily pass 180 volts right into your computer and microwave. Then it’s new appliance time.

TO TAKE CARE OF THIS SITUATION, companies such as Progressive Industries build a voltage monitoring device which checks the incoming voltage for correct levels and will trip a relay to disconnect your coach from the power pedestal if it goes above or below a set limit. Those same voltage-monitoring devices generally include a MOV “surge protector” which will get rid of the quick “spikes” that the relay can’t act quickly enough to disconnect.

Checking around, the $300 “surge” device you’re probably referring to is a voltage monitor with disconnect relay that goes between the shore power plug and campsite pedestal. For instance the Progressive Industries EMS-PT30C has both surge protection from nearby lighting strikes and voltage protection from over and under voltage conditions as well as reversed polarity on miswired campsite pedestals and extension cords. It includes a readout that will display any power problems as well as notify you when your MOV devices need to be replaced. See here to learn more.

Progressive Industries also makes just a surge protector for $99 that will stop the surge (voltage spike) caused by a lighting strike in the area or a water pump switching off. And it also includes monitoring lights to tell you if its own MOV circuits have been worn out by too many spikes. However, it can’t shut off your power if the voltage swings below 90 or above 130 volts. In that case, your appliances could fry while the surge protector MOV sits there perfectly happy. Click here for more info on their surge/spike protectors.

In either event, I talked to Tom Fanelli at Progressive industries about MOV replacement in their products, and he said they would replace the worn-out MOV devices in their products for free if you paid for shipping one-way to them. They’ll then ship it back to you for free. That’s a fantastic deal!

However, both of these aforementioned devices are WAY BETTER than the $20 “surge strip” you may have your computer plugged into. These extension cord surge strips have smaller MOV devices, so they can only dissipate much smaller “surges” and often don’t have an indicator light to tell you they’re worn out. And they will do nothing to protect your inverters or built-in RV appliances.

I would get some sort of overall protector on the shore power connector. So do you spend $99 on an RV “surge protector” or $300 to $500 on a “voltage protector”? Well, that’s up to you. But considering that the cost of an RV refrigerator or microwave can be $1,000 and up, plus the cost of all the electrical things you plug in like computers, iPods, phone chargers, etc, I think the $300 to $500 of a voltage protector to be well worth the investment, and probably costs less than the deductible on your RV insurance policy.

And yes, there are a number of other manufacturers who make voltage protectors and surge protectors for RVs. But I’ve studied the Progressive Industries gear the most so I’m just more familiar with them. Perhaps I’ll review a number of Voltage and Surge Protectors in a future article.

FYI: If you’re within easy driving distance of Hagerstown, MD on Saturday, June 18, 2011, I’ll be presenting a NoShockZone seminar at Keystone RV Wholesalers sometime in the morning. I don’t have all the event details yet, but I’ll be showing live examples of RV hot-skin testing, over current conditions on extension cords, and proper RV and appliance grounding. It’s a free event and clinic, and you’ll have some fun while learning all about RV electrical safety from me. Shoot me an email at mike@noshockzone.org for more information as it comes in.

Please send us your comments and suggestions. We’d love to know how we’re doing with this important project.

Mike Sokol is the chief instructor for the HOW-TO Sound Workshops (www.howtosound.com) and the HOW-TO Church Sound Workshops. He is also an electrical and professional sound expert with 40 years in the industry. Visit www.NoShockZone.org for more electrical safety tips for both RVers and musicians. Contact him at mike@noshockzone.org.

RV Electrical Safety: Part XI — Extension Cords

Mike Sokol — Tue, 09 Nov 2010 19:34:57 +0000

The No~Shock~Zone: Part XI — Extension Cord Testing

Understanding and Preventing RV Electrical Damage

If you’ve read the survey we did July 2010 in www.RVtravel.com, you know that 21% of RV owners who responded have been shocked by their vehicle. Review the 21% report at http://www.noshockzone.org/15/. What follows is #11 in a 12-part series about basic electricity for RV users and how to protect yourself and your family from shocks and possible electrocution. In addition, this series could protect your RV’s appliances, entertainment systems and computers from going up in smoke.

The Lowly Extension Cord

Few objects in an RV get less respect than the lowly extension cord. They’re kicked around, stepped on, run over, and dragged through the mud. And most of the time they don’t even get wrapped up neatly. No, they’re often thrown unceremoniously into a tangled heap, then plugged in and expected to pass more current than they were ever rated for. If you don’t know how much current your extension cord can safely pass without overheating and catching on fire, please re-read “RV Electrical Safety: Part V – Amperage”.

That being said, please check that your extension cords are heavy enough to supply the amperage needed by your RV before proceeding with any testing or repairs.

The Ends

Here’s what the ends of a typical 20-amp extension cord looks like. Notice there’s a male plug on the left side of the picture, and a female plug on the right side. Most everyone should already know that the female plug is the power “output” while the male plug is the “input”. That is, the bare metal pins of the male plug on the left should never be electrically energized while it’s out in the open, but the female plug can be electrically “hot” at any time. Also note the orientation of the plugs. While holding them both facing you, the sideways “neutral” blades are reversed on the left and right side of the picture. That is, the male plug has its neutral blade on the left, while the female plug has its neutral blade on the right. That’s because they’re designed to be rotated 90 degrees to mate when making a connection, in which case the neutral, hot, and ground blades will match up. This single idea is what gets lots of RVers in trouble when putting a new plug on an extension cord.

Exploratory Surgery

If you’re not comfortable looking inside an extension cord plug, then please find someone with an electrical background before proceeding. And please make sure that both ends are unplugged from power before taking anything apart. Even 120 volts can be deadly, so be careful.

White is Neutral

In previous NSZ articles you’ve read about different color wires and screws, so here’s a close picture of what it looks like. Note that the extension cord wire itself has a white colored insulation which is stripped back to let the bare copper go under the white colored screw. That’s the neutral connection we’re always talking about.

Green is Ground

And here’s what the green ground wire looks like properly placed under the green screw. Note that in extension cords that wire will actually have a green insulation layer as shown, but installed Romex wiring within your home or RV electrical panels will have a completely bare copper wire that’s the ground connection.

Black is Hot

Finally, here’s the black “hot” wire under the brass colored screw. If you’ve read any of the previous NSZ articles you’ll know how important it is to follow this color code. Anything different is not only illegal, but can cause a dangerous Hot-Skin condition on your RV.

Measurements

If you don’t remember how to use a Digital meter, please go back and reread RV Electrical Safety: Part II – Meters

Note that this is the only time you’ll set the meter to read “ohms” or “continuity”. And you must be certain there is no AC voltage on the plugs before inserting the meter leads or you’ll “blow” your meter”. In this case I’ve set my Triplett pocket meter to “continuity test” which will “beep” when the meter leads are touched together. That indicates a complete circuit which is what we’re looking for in this test.

Hot Test

Notice that when both plugs are facing you, the neutral and hot blades will be on the opposite sides of the plugs. For example, the female plug has the hot blade on the left side, while the male plug has the hot blade on the right side. Again, that’s because when the plugs are rotated 90 degrees to plug into each other, the hot, neutral and ground blades need to line up. You should hear your meter “beep” when touching both hot blades at the same time as shown above, but for no other combination of connections.

Neutral Test

The same idea holds for the neutral blades. Notice that for a 20-amp plug the neutral blade is turned sideways. If you see a plug with both neutral and hot in the same direction (parallel) then that plug is only rated for 15 amps of current. Again, your meter should “beep” when touching both neutral blades at the same time, but for no other combination.

Ground Test

Finally, check for continuity of the ground blade. It’s always the little U-shaped slot or blade and typically has a green colored screw on the back, so the usage is pretty obvious. Green is always ground (in the USA, at least).

Color Code

You’ll want to double-check the wire colors of the connections in any repaired extension cord. That’s because something as simple as reversing the black (hot) and green (ground) wires in an extension cord will certainly electrify the skin of your entire RV. There are electrical safety systems from Progressive Industries and others that will shut off the power coming into it if wired incorrectly. But be aware that unless they’re hard-wired into your RV’s electrical system, it would still be possible to defeat their safety function if you then used an improperly wired extension cord from their output into your RV.

Also, always be aware of any tiny “tingles” you may feel when stepping into your RV from the wet ground. There should be essentially zero volts from the earth to the frame of our RV at all times. Anything more than a volt or two means that something has been wired improperly, either at the campsite pedestal or perhaps inside your extension cord. So don’t proceed if you feel a shock of any kind. Shut down the pedestal breaker and get the campsite electrician to determine what’s wrong with the hookup that’s causing a shock. The life you save might be your own.

Wrap Up

There are a number of extension cord wrapping gadgets available, any of which is better than letting your wires become a tangled mess. I think they’re a good investment. Also, remember to visually check for any kinks or slits in the outer insulation of your extension cord, and certainly any exposed copper wire is a big no-no. Also, if you notice that the brass colored blades on the plugs are discolored or the plastic is brown due to overheating, it’s time to replace the cord, or at least replace the plugs. Once a female plug overheats, the tension of the internal contacts is lost, which causes more heating that leads to more lost spring tension, which eventually leads to a brown-out (low voltage condition) or even a fire. So take care of your extension cords, and they’ll take care of you.

You Get What You Pay For

In the end, paying a little more money for a quality product is the best way to go. The orange molded extension cords you get from the big box stores are usually not heavy enough for rugged RV usage and they tend to get hot and catch on fire when pulling any sustained amperage (ask me how I know that). So heavier and shorter is better when it comes to selecting an extension cord to power your RV.

Future Shock

Part XII of this series will cover what to do if you find someone who’s been shocked and knocked out. So come back next week for a basic lesson in compression only CPR. See you then.

Feedback

After you’ve read this article at www.RVtravel.com, take a trip over to www.NoShockZone.org and send us your comments and suggestions. We’d love to know how we’re doing with this important project.

RV Electrical Safety: Part X – GFCI Testing

Mike Sokol — Mon, 25 Oct 2010 17:48:31 +0000

The No~Shock~Zone: Part X — GFCI Testing

Understanding and Preventing RV Electrical Damage

If you’ve read the survey we did July 2010 in www.RVtravel.com, you know that 21% of RV owners who responded have been shocked by their vehicle. Review the 21% report at http://www.noshockzone.org/15/. What follows is #10 in a 12-part series about basic electricity for RV users and how to protect yourself and your family from shocks and possible electrocution. In addition, this series could protect your RV’s appliances, entertainment systems and computers from going up in smoke.

GFCI review

If you don’t already know what a GFCI circuit breaker is, please read part VIII on basic theory and operation of this lifesaving device. GFCI devices are among the least understood of all electrical safety circuits, but their function is really pretty simple once you understand their basic operating principles.

It’s All About Balance

Here’s the illustration we used in Part XIII to demonstrate what a GFCI is looking for electrically. Note that a perfectly isolated electrical appliance should have exactly the same amount of electrical current going out and coming back in. For example, if an applicance draws 7.000 amperes of current from the black/hot wire, then exactly 7.000 amperes of return current should be coming back in the white wire. However, if there’s any secondary connection to the earth/ground from something like our happy camper poking a piece of metal in a socket while standing on the ground, there will now be more current going out the black wire than is returning from the white wire.

GFCI breakers in America are designed to trip when there’s any more than 5 milliamperes (5/1000 of an amp) of difference between the black and white wires. Note that a GFCI breaker doesn’t really need the green/ground wire at all to function. The GFCI detector circuit only cares about what’s going out of the black wire compared to what’s coming back into the white wire.

Nuisance Tripping

What bothers many campers and home owners about GFCI breakers is that they’ll occasionally trip for no apparent reason. So if you plug your shore power to the GFCI outlet in your garage to run your RV refrigerator while you’re stocking for an extended trip next week, you may come back the following day to find the power out and your food spoiled. Nobody was in the RV and nothing looks out of place. Or you plug in a power drill to your exterior RV outlet and BAM! it trips before you can pull the trigger on the drill. Why would that happen when the drill runs just fine in your basement workshop? Those sorts of situations are what makes home and RV owners suspicious of GFCIs and want to replace them with a non-protected outlet — which, I might add, is illegal to do.

Less Than Perfect?

What could cause an appliance or electrical circuit to behave badly and fool a GFCI into tripping? Glad you asked. Every appliance has at least two separate wires connecting it to the power outlet, and many will have a third “green” wire known as the safety ground. The purpose of this ground wire is to drain off any electrical leakage within the appliance itself that might occur from deteriorated insulation, a pinched wire or perhaps a failed component such as a power transformer or light bulb socket with water inside.

This deterioration or component failure often occurs in old electrical appliances. So if you’re plugging in a Fender guitar amp from your teenage years, the amplifier probably has a lot of heat damage to the power transformer from those extended bar jams of “Smoke on the Water.” That overheating is what causes that peculiar “burnt transformer” smell that we also associate with a bad fluorescent light ballast.

An appliance’s or amplifier’s insulation breakdown doesn’t always result in a complete short circuit that would trip a regular 20-amp circuit breaker. It can be like a small leak in a pipe that’s dripping water just a bit. So let’s assume that there’s 10 milliamperes of electrical leakage from the hot/black wire of the power cord to the chassis of your amplifier. That’s way less than the 3 or 4 amperes of current your amp is drawing from the circuit to run the tubes and power the speakers. Therefore, a 20-amp circuit breaker thinks that all is well. However, plug that same guitar amplifier into a GFCI breaker and it sees there are 4.010 amperes of current going to the black wire and only 4.000 amperes of current coming back from the white wire. Where did those extra 10 milliamperes (0.010 amps) of current go? Well, back through the green wire that ties to the white wire way back at the electrical panel. But since the GFCI doesn’t know or care if that extra 10 mA of current was properly disposed of via the green ground wire or your hand touching the electrified chassis of the amplifier, it trips the breaker in an attempt to save your life. Let’s not call this nuisance tripping, but rather life-saving tripping.

Charting Fault Combinations

So here’s two ways to determine which of your appliances is tripping the GFCI. The first is pretty simple. Just unplug every appliance from its own electrical outlet and begin plugging them back in one at a time and turning them on. You’ll want to cycle the appliance on and off a few times since there can be ground fault current “spikes” when you turn on a microwave or light switch. But here’s where it gets tricky: ground fault currents are additive. So if you have two appliances that are each leaking 4 mA (milliamperes) of current to ground, turning on either one of them won’t trip your GFCI, but turning on both appliances at the same time will allow their fault currents of 4 mA and 4 mA to add up to 8 mA. And, of course, 8 mA is greater than the 5 mA limit of the GFCI breaker so it trips.

This might require a little detective work, but I usually make a simple chart or spreadsheet of all my appliances and turn them on singly and in combination with every other possible appliance. Charting seems like an unnecessary step, but that’s when you’ll see obvious combinations that cause a problem, like in my chart above. It shows that when I turned on both the porch light and the microwave, the GFCI would trip. Now I know there’s something electrically leaking to ground in both the porch light and microwave. The porch light might have a water leak in the wall, which is letting moisture into an unsealed electrical box, while the microwave could have a chafed wire from bouncing down the highway for the last few years. Both problems should be corrected since they’ll only get worse, not better, with age.

Measure It

There is, however, an even better method if you’re an RV tech or can borrow or buy a clamp-on ammeter such as the Fluke shown in the picture. To do this properly you’ll need a meter that can display down to 0.001 amperes, which is 1 mA resolution. Clamp-on ammeters have a current transformer that looks for current flowing through the wires placed inside their jaws. However, if you simply clamp them around the entire power cord of an appliance, you’ll be summing the current going out from the black wire with the currents returning from the green and white wires and you won’t know the actual ground leakage current. Because the GFCI ignores the green wire current in its own leakage calculations, we need to do the same thing with our clamp-on ammeter to get the real current levels involved.

You can do this ground fault leakage test by sacrificing a short extension cord to make a test cable. (Don’t you feel like a scientist, now?).

With the extension cord unplugged from everything, just slit off the outer covering, being careful not to nick the insulation of the black, white or green wires. Get rid of any nylon filler and untwist the group of wires until you get something that looks like the picture to the right.

This is perfectly safe to use for testing, but because you’ve removed the outer protective layer of insulation, you’ll need to retire this particular extension cord from your regular hookup inventory. That why I typically do this modification to a short 6-ft extension cord which I then keep on my test bench.

This modification allows you to plug your appliances one at a time into a non-GFCI outlet using your test cable to see how much current is leaking back to ground.

Clamp the ammeter around the black (hot) and white (neutral) wires as shown in the picture, keeping the green (ground) wire out of the jaws.

Your ammeter will now be registering how much current is going out the black wire minus how much is coming back the white wire. So any currents you read on the meter will be the ground leakage that can cause the GFCI to trip from that appliance.

Note that there’s going to be a certain amount of leakage to ground from anything plugged into a wall outlet. So 1 mA or so is not a problem. In this case I have 0.0008 amps which is 0.8 mA of current flow, just less than 1 mA. That by itself shouldn’t cause a GFCI to trip. But you can see that if you have five appliances plugged into a single GFCI (like a campsite 20-amp receptacle) and each one is leaking around 1 mA of current to ground, then that GFCI breaker is going to trip whenever it feels like doing so.

Troubleshooting each appliance for ground fault leakage is beyond the scope of this article, but once you’ve identified the problem, you can either replace or repair each item, checking again with your clamp-on ammeter to confirm you’ve fixed the current leak to ground. Once your total ground leakage current is below 5 mA, then your random GFCI tripping should become a thing of the past.

Wrap Up

GFCI breakers always trip for a reason, and that reason is that they see an imbalance between how much current is going out to an appliance from the black wire compared to how much is coming back in from the white wire. If you clamp an ammeter around the black and white wires at the same time, any current flow detected will be ground leakage within the appliance itself. Over 5 mA of leakage to ground is supposed to trip a residential GFCI, so it’s only doing its job.

Future Shock

Part XI of this series will cover extension cord wiring and testing, so come back next week. See you then.

Feedback

Mike Sokol is the chief instructor for the HOW-TO Sound Workshops (www.howtosound.com) and the HOW-TO Church Sound Workshops. He is also an electrical and professional sound expert with 40 years in the industry. Visit www.NoShockZone.org for more electrical safety tips for both RVers and musicians. Contact him at mike@noshockzone.org.

RV Electrical Safety Part IX – In Review

Mike Sokol — Tue, 12 Oct 2010 12:25:20 +0000

No Shock Zone RV in Review

I’m using this week’s column in a two-fold manner: 1) As a review of where we are in this 12-part series on RV electrical safety; and 2) As a call to action.

We’ve now completed Part VIII of this series, and have only four more RV safety articles scheduled. (See below for what’s been covered so far.) Part IX will be on GFCI troubleshooting; Part X on extension cord rewiring; and Part XII will be on basic CPR techniques — in the event of an electrocution. (I haven’t decided what Part XI will be just yet, but perhaps it will touch on electrical safety around boat docks since many of you also enjoy boating.)

I’m glad to study and write about electrical safety, and have received many positive comments about the clarity and benefit of these articles. I would like to continue to add more articles in the future. So here’s how you can help.

Let us know any topics you’d like to see covered in future articles. For example, portable generator grounding is a big issue, and topics such as 12-volt DC battery safety are vitally important, especially around RV house batteries and inverters. If you have any electrically-related areas of concern, please send me an e-mail.
Please pass along the www.RVtravel.com and www.NoShockZone.org links to any other forums you belong to. We see referrals from a diverse group of RV forums such as Airstream, Monaco, Women in RVs, etc, but the more the merrier.
Suggest any RV-oriented magazines that might run these articles in any form. Any magazine or print suggestions or referrals would be appreciated.
We are looking for experts in the various electrical fields to confer with us on these and more advanced topics. For instance, an EE designer who builds portable generators for the RV industry could answer questions on grounding for us all.
We’re looking for invitations to present NoShockZone clinics across the country. We’ve already talked to a few large campgrounds, but if you know of any places that could act as a host site, we’re all ears. We see NSZ clinics as a valuable addition to trade shows, RV dealerships and RV Rallies of all sorts. Since I already travel all over the country teaching hands-on sound mixing classes (www.HowToSound.com) it would be possible to schedule an afternoon at a campground for a NSZ clinic as I’m driving through around Texas or Oregon or Florida. Hey, I drove 50,000 miles last year alone, so this would be a nice break from seat time on the road.
Sponsorship support for these clinics is what’s really needed. You can see that www.NoShockZone.org is a new site that presently has zero sponsors. These electrical safety articles are written for no compensation except for the knowledge that we’re educating folks and quite possibly saving lives. And Chuck Woodbury from RVtravel.com sees this as having such importance that he’s created an entire NoShockZone area for past and future articles on his site.

However, to put these clinics on the road in 2011 we’ll require sponsorship support. Manufacturers of many types should be interested in providing such support. Those of you who have read this series so far know that its purpose is to protect the typical RV user by informing them on how to identify and avoid dangerous electrical situations. Companies that manufacture electrical test equipment or electrical cables and extension cords or even insurance companies should jump onboard our educational safety RV.
And we know that many of you are also concerned about damage to your RV’s electrical appliances and the cost of their replacement.

With that in mind I would suggest that personal shock safety and RV appliance damage really involve the same skill sets. A properly connected RV is intrinsically safe for both its appliances and occupants. So everyone wins if more people understand the basics of electricity and how to properly inspect an RV electrical hookup.

If you know of a RV manufacturer, educational grant or safety foundation that might lend monetary support to the NoShockZone clinics, tell them about us, and please introduce us to them. We really need your help to put these educational safety clinics on the road. Contact me at mike@NoShockZone.org and I’ll get back to you within a day.

Thanks for your suggestions, and thanks for reading.

Mike Sokol
mike@NoShockZone.org

NSZ-RV Review

RV Electrical Safety: Part VIII – GFCI

No it’s not the name of an insurance company or a European sports car, GCFI is an abbreviation for Ground Fault Circuit Interrupter or G-F-C-I. They’ve been required in many localities for electrical outlets located near sinks or the outside of your house for the last 10 years or more.

RV Electrical Safety: Part VII – Wattage

If you’ve been reading along this far in the series you already know about voltage (electrical pressure) and amperage (current flow). You also know how to measure voltage using a DMM (Digital Multi Meter) and how to size extension cords for sufficient amperage (current) capacity. But in the end it all comes down to wattage.

RV Electrical Safety: Part VI – Voltage Drop

We’ve all heard about how hooking up an RV on too long or too skinny of an extension cord can force its appliances to run on 100 volts instead of the regular 120 volts, thereby burning out the motors or other components. But before we get into the reality of what happens to gear running on 100 volts rather then a full 120 volts, let’s figure out why this voltage drop thing happens in the first place.

RV Electrical Safety: Part V – Amperage

For those of you unfamiliar with extension cord and wire specifications, the lower the number of the gauge, the thicker the wire and the more current that can flow through it without overheating. For example, a 14-gauge extension cord might be rated for only 15 amperes of current flow, while a 10-gauge extension cord could be rated for 30 amperes of current, depending on total length of the cable and type of insulation.

RV Electrical Safety: Part IV – Hot Skin

An RV Hot-Skin condition occurs when the frame and body of the vehicle is no longer at the same voltage potential as the earth around it. This is usually due to an improper power plug connection at a campsite or garage AC outlet. So what follows are two ways to determine if the skin of your RV has been electrified. The first method uses a voltmeter for testing, while the second method uses a non-contact AC tester like electricians use to check for live outlets.

RV Electrical Safety: Part III – Outlets

Today’s RVs have much greater power requirements than those of even 10 years ago. You’ve got lots of appliances, so that single 20-amp outlet can’t provide enough current. This is when you need to step up to 30- or even 50-amp outlets at the campsite. Let’s see how they’re wired.

RV Electrical Safety: Part II – Meters

Remember when you were a child and first started to help with baking there were all sorts of measuring devices and abbreviations to take into consideration? There was a Tablespoon (Tbsp), teaspoon (tsp), Ounce (oz.), with 8 oz. in a cup, and so on. And you better not get your tsp and Tbsp mixed up or bad things would happen to your cake. The same types of rules apply when you’re measuring any electrical values. You just need to know how to use a few electrical measuring tools and then you’re ready to test your RV power.

RV Electrical Safety: Part I – Volts

While RV’s as wired from the factory are inherently safe, they can become silent-but-deadly killers if plugged into an improperly wired extension cord or campsite outlet. This is because RV’s are basically a big cage of metal insulated from the ground by rubber tires. It’s up to you, the RVer, to make sure the frame and body of your RV is never electrified due to poor maintenance, bad connections, or reversed polarity in a power plug. This so called Hot-Skin problem is what causes a tingle when you touch the doorknob or metal steps of your RV while standing on the ground.

The Shocking Truth About RV’s

We’ve been trying to locate a study on just how many RV owners have been shocked by their recreational vehicles, but search as we might, nobody seems to have done a study. So last July we asked www.RVtravel.com to run a simple 10-second survey directed to their 85,000 opted-in newsletter readers, and we found that 21% of you report getting shocked from your RV.

RV Electrical Safety: Part VIII – GFCI Theory

Mike Sokol — Thu, 30 Sep 2010 12:26:36 +0000

The No~Shock~Zone: Part VIII — GFCI Theory

Understanding and Preventing RV Electrical Damage

If you’ve read the survey we did July 2010 in www.RVtravel.com, you know that 21% of RV owners who responded have been shocked by their vehicle. Review the 21% report at http://www.noshockzone.org/15/. What follows is #8 in a 12-part series about basic electricity for RV users and how to protect yourself and your family from shocks and possible electrocution. In addition, this series could protect your RV’s appliances, entertainment systems and computers from going up in smoke.

GFCI?

No it’s not the name of an insurance company or a European sports car, GCFI is an abbreviation for Ground Fault Circuit Interrupter or G-F-C-I. They’ve been required in many localities for electrical outlets located near sinks or the outside of your house for the last 10 years or more. The two types of GFCIs you’ll encounter are either built into the power outlet itself (left in the illustration) or inside the circuit breaker at the power panel (right in the illustration). Both do exactly the same thing: they watch for electricity that’s going someplace it shouldn’t in an electrical Circuit by way of a Fault to Ground and then Interrupt the flow by tripping the circuit breaker. Rearrange the letters and you get G-F-C-I for Ground Fault Circuit Interrupter. That’s how the name is derived.

Why Do We Need a GFCI?

Well, if you’ve been reading along from Part I of this series, you’ll know that your heart muscle is very sensitive to electrical shock. While it takes around 8/10ths of an amp (800 milliamperes) of current to power a 100-watt light bulb, it takes less than one percent of that same current (5 milliamperes) to send your heart into fibrillation, causing death by electrocution. That’s why the NEC (National Electrical Code) now requires a special type of circuit breaker for damp locations that can tell the difference between the normal currents feeding an electrical appliance and the currents accidentally flowing through you to ground. And while a GFCI sometimes trips unexpectedly, it’s really there to save your life and the life of your appliances and other electrical components.

How Does a GFCI Work?

It’s a pretty ingenious system that uses a small current transformer to detect an imbalanced current flow, so let’s use our water pump analogy to review the typical current path in a standard electrical circuit.

As you can see from the illustration, we have our pump and turbine system again. And let’s imagine the pump at the top is pushing 7 Gallons Per Minute (GPM) of water current around in a circle that our little turbine at the bottom is happily using to spin and do some work.

I’ve added flow meters at the bottom left and right of the illustration so we can keep track of these currents. Now since our pipes have no leaks, the current going out of the pump from the black pipe will exactly equal the return current coming back in the white pipe. And this will be an exact balance since no water is lost in this closed loop. That is, if 7.000 GPM (Gallons Per Minute) of water are flowing out of the black pipe, then 7.000 GPM will be returning to the pump via the white pipe. There are no water losses in this perfect system.

Keeping in Balance

Let’s add an extra meter in this system so we can keep track of the water flow a little easier. Notice there’s now a center meter that will show you the difference in flow between the other two meters. If the left and right meters show exactly the same water flow, the center meter will show zero GPM of flow by centering its needle.

This is exactly what should happen in an electrical circuit that’s working properly. That is, if a light bulb has exactly 1 amp of current flowing out from the black (hot) wire, then exactly 1 amp of current should be flowing back in the white (neutral) wire. And an electric griddle that has 10 amps of current flowing out the black wire should have exactly 10 amps of current flowing back in the white wire.

If there’s nothing wrong in the light bulb or griddle circuit, this electrical current balance will be pretty close to perfect, out to at least 3 decimal places. That is, 10.000 amps of current flow going out will equal 10.000 amps of current flow coming back in.

Out of Balance

Now I’ve added a leak in the black outgoing pipe via the red pipe sticking out to the left. You can see from the red pipe’s meter that 5 GPM of water is flowing out onto the ground. And since only 7 GPM of water is coming out of the black pipe on the pump, there can be only 2 GPM of water returning into the white pipe on the right.

Those 5 GPM of imbalance show up in our center balance meter, which alerts us to the fact that there’s a leak somewhere in the system. Now, we really would like to know about small leaks as well, so that center meter will tell us about an imbalance down to very small drips, say less than 1/1000 of a GPM.

The same is true of our electrical circuit where we’re interested in currents in the 1/1000 of an ampere range (1 mA or 1 milliampere). That’s because just a few milliamperes of misdirected current flow is close to the danger level for stopping your heart.

Teeter Totter

In an electrical system, a similar type of detector is used at the center of the circuit which is acting like a balance beam. So if 7 amps of current shows up on both sides of the balance, then the beam will be exactly level. However, put 7 amps of current on the left side and 2 amps of current on the right side, and that 5 amps of imbalance will tip the scales, just like the teeter totter ride you took with your dad when you were maybe 50 years younger and a 150 pounds lighter. In our GFCI circuit this is a much more sensitive balance beam that only needs 5 mA (5 milliamperes or 0.005 amps) of current imbalance to tip over rather than the 5 GPM we’ve shown in the water pump illustration. The reason for needing this much sensitivity is that our hearts can go into fibrillation from just 5 mA of AC current flow, so we would like to detect and stop that flow before it stops your heart.

Putting It All Together

So here’s where it all comes together. Notice that our guy is unwisely touching a hot wire with a hand while his foot is in contact with the earth. And while the electrical outlet might have been supplying 7.000 amps of outgoing current to an appliance with exactly 7.000 amps of return current, there are now 7.005 amps going out and only 7.000 amps coming back. Those extra 0.005 amps of current (5 milliamperes) are taking a side trip from his hand to his foot via the heart. And the current balance circuit inside the GFCI is sensitive enough to recognize that imbalance and trip the circuit open with as little as 5 or 6 milliamperes of current flowing someplace it shouldn’t be going.

The click you hear when a GFCI trips is its spring loaded contact opening up and interrupting the current flow in the circuit before it causes electrocution. That’s the entire GFCI’s reason for existence, to save you from electrocution and keep your RV’s electrical system safe from damage. Pretty cool, eh?

Also note that the GFCI doesn’t really need a direct ground connection via the ground wire to do its job. Yes, one is required to properly “earth” the entire circuit, but the current balancing act is only between the black and white wires going to the outlet. If the current flow in the white wire exactly matches the current flow in the black wire to within 5 mA (milliamperes), the circuit stays activated. If the current flow is unmatched by any more than 5 mA, say by someone touching a live wire and the earth at the same time, then the trigger circuit inside trips a little switch and the current flow is stopped. It’s that simple.

All this means you should install GFCI breakers where required, and don’t remove or bypass them if there’s false “nuisance” tripping. That so-called false tripping hints there’s something else wrong in your RV electrical system that’s leaking out current to someplace it doesn’t belong. And fixing that electrical leak is important since if you get your body in the middle of the current leak it can shock or even electrocute you.

Future Shock

Part IX of this series will cover why false GFCI tripping occurs and how to troubleshoot for it, so come back next week. See you then.

Feedback

Mike Sokol is the chief instructor for the HOW-TO Sound Workshops (www.howtosound.com) and the HOW-TO Church Sound Workshops. He is also an electrical and professional sound expert with 40 years in the industry. Visit www.NoShockZone.org for more electrical safety tips for both RVers and musicians. Contact him at mike@noshockzone.org.

Stage Electrical Safety – Part II: Meters

Mike Sokol — Wed, 29 Sep 2010 19:58:30 +0000

The No~Shock~Zone

Stopping Hums, Buzzes and Shocks on Stage
Part II: Meters

©Mike Sokol 2010 – All Rights Reserved. If you’ve read the survey we’re running at www.prosoundweb.com, you’ll discover that 70% of the musicians and sound technicians surveyed have been shocked by their mics, instruments and sound systems. What follows is the second in a 12-part series about basic electricity for performers and technicians and how to safely stop hums, buzzes and shocks from your amps and equipment. Review the 70% report at http://www.noshockzone.org/musician-shock-survey-in-progress/.

This series of articles is provided as a helpful educational assist with sound system setup and musical performance, and is not intended to have you circumvent an electrician or qualified audio technician. The author and the HOW-TO Sound Workshops will not be held liable or responsible for any injury resulting from reader error or misuse of the information contained in these articles. If you feel you have a dangerous electrical condition in your PA system or instruments, make sure to contact a qualified, licensed electrician or audio installer.

Just the Facts

In Part I of this No~Shock~Zone Stage series you learned what voltage is and a bit on how it’s measured. In this article we’ll cover how to use a basic digital voltmeter to measure any power outlet or extension cord for proper voltage. The reason this procedure is so important is that sometimes venues do crazy things with power outlets. For instance I was teaching a seminar last year in a “gymnatorium” and plugged in my little demo rack along with my RF headset receiver. As I was getting ready to flip the switch on the Furman rack distro, I noticed the built-in voltmeter was pegged to the right of the 120 volt scale. Luckily, I didn’t go further and did not flip on the switch that powered the full rack. But unluckily for my RF receiver, it was ahead of the Furman power switch so it was already “on” and burning quite brightly for a few seconds. A quick meter test on the power outlet confirmed it had been jury-rigged for 240 volts, even though it was a standard NEMA-5 “Edison” outlet, which should always be wired for 120 volts. The janitor told me that was his “special outlet” they had rewired for his 240-volt [floor] buffer. But it should have had a 240-volt plug and outlet, not an Edison outlet modified for 240 volts. My bad for not checking. My RF receiver was toast, but all the rest of my gear was fine. Live and learn….

Shake & Bake

Remember when you were a child and first started to help with cooking, and there were all sorts of measuring devices and abbreviations to take into consideration? There was a Tablespoon (Tbsp), teaspoon (tsp), Ounce (oz.), with 8 oz. in a cup, and so on. And you better not get your tsp and Tbsp mixed up or bad things would happen to your cake. The same types of rules apply when you’re measuring any electrical values. You just need to know how to use a few electrical measuring tools and then you’re ready to test your stage power.

The Meter

Now is the time to familiarize yourself with your voltmeter. Here’s a pretty typical $30 meter that you can purchase at Lowes, Home Depot or Amazon. You’ll notice a bunch of strange markings on the selection knob, only a few of which will work to measure AC voltage. Don’t be tempted to just plug the meter leads into a wall outlet and spin the knob. That will guarantee a burned out meter (at the least).

Note the markings on the control knob are divided up into four major groups.

AC V (AC voltage)
DC A (DC amperage)
OHM (electrical resistance)
DC V (DC voltage)

The only two groups you’ll be interested in for measuring voltage are AC V (for measuring the AC voltage in power outlets) and DC V (for measuring the DC voltage in your batteries). For this article we’ll focus on the AC V group since we’re measuring the 120 or 240 volts AC in a wall outlet or stage power distro.

Also take a look at where the meter leads are plugged into the lower right-hand connections. The Black COM (common) input is always connected to your black meter lead, and the red V Ohm mA (milliamperes) input is always connected to your red meter lead. Never put either meter lead into the 10A socket, which is designed specifically to check current flow. Doing so will blow the internal fuse in the meter, and possibly damage the meter itself.

All meters read the difference between the two lead connections, so if the black lead is touching 0 volts and the red lead is touching 120 volts, the meter will read 120 volts. However, if both the red and black leads are touching 120 volts, the meter will indicate 0 volts, which is because 120 minus 120 equals 0. See how it works? That’s the key to using a meter. It must be connected between the two voltages you want to measure.

Now, let’s move back to the meter settings. In the AC V area you’ll see a 200 and a 750 setting. When set to 200 the meter will read up to 200 volts, when set to 750 the meter will read up to 750 volts. Since we could be reading as much as 250 volts in a standard electrical outlet, we’ll always just set this to 750 and leave it alone during all testing. If you set it to 200 and connect it to a 240 outlet, the display will probably stick on 200 Volts and start blinking. That doesn’t hurt anything in the meter, but it doesn’t tell you the actual voltage. Many meters of this type have a 400- or 600-volt setting, so setting for 400 or 600 volts is fine as well, just as long as it’s set for something more than 250 volts. And if you have an auto-ranging meter, just set it to read AC volts and it will figure out the proper scale for you.

The Outlet

Let’s start on a common 120-Volt, 20-Amp outlet like you might find in your living room or on any American stage. Here’s what one looks like, and the connections as standardized by the National Electrical Code. You’ll see a little U-shaped hole: that is the Ground; a taller slot on the left, which is the Neutral; and a shorter slot on the right, which is the Hot connection. Don’t be confused if the receptacle is mounted upside down with the ground connection to the top. The taller slot is always the NEUTRAL, and the shorter slot is always the HOT.

This is a GFCI (Ground Fault Circuit Interrupt) receptacle so there are test and reset buttons. More on this later, but pushing the “test” button should cause the “reset” button to pop out and kill the power from the outlet. Pushing the “reset” button in until you feel a click will restore power to the outlet. The job of the GFCI is to kill the power to the plug before it kills you, say from a hot chassis condition on your guitar amp. But much more on GFCI operation in a future article.

Generator and Distro Power

If you’re working on a large stage with dedicated power or an outside venue fed by a generator, you’ll often bring along your own electrical distribution system know as the “power distro”. And many times that power distro system will be fed by large twist-lock connectors generically know as Cam Locks. These are big brass connectors the size of a banana with rubberized insulating covers that keep you from getting shocked while touching the exterior. They come in colors corresponding to their connection type, so a green cam lock is ground, white is neutral, and black, red, or blue are hot (at least in America). Sometimes the cam lock covers will all be black with a wrap of white, green, blue or red electrical-tape in the middle to define their usage and that’s legal as well.

Here’s what a portable distro panel looks like with the green, white, black and red cam lock inputs across the bottom. Cam locks are typically fed by a single, double or triple 100 to 200 amp circuit breaker at the generator or house panel, so you’ll need to provide your own 20-amp breakers downstream to feed your portable backline power outlets in order to prevent the wires from melting in the event of an overload. You can see the circuit breakers across the top of the panel at the left. Also, you’ll occasionally find a 3-phase house system with green, white, red, black and blue cam locks which will meter as 120/208 volts, but we’ll discuss that topic towards the end of this series.

Also note the difference between the 20-Amp and 15-Amp versions of the stage outlets as shown a few illustrations back. A 20-amp outlet will have another sideways slot for the neutral connection, while a 15-amp outlet will only have a single vertical slot.

The Measurements

Since we’re going to be measuring live voltage, you need to observe the safety rules from Part I of this series:

Use only one hand to hold the plastic handles of the meter leads, put your other hand in your back pocket so you don’t lean it on anything conductive;
Be sure you don’t touch the metal tip portion of either meter lead;
Don’t stand or kneel on wet ground while testing voltages. For most situations, dry sneakers will insulate you from the earth sufficiently, and if you’re doing this test on a dry stage then the wooden floor or carpet will protect you if something goes wrong. But if you’re going to measure voltage at a waterlogged festival generator I suggest standing on a dry rubber shower mat or dry plywood so your feet are insulated from the ground. It’s cheap insurance.

Hot to Neutral

With nothing plugged in to the wall outlet, switch on the 20-Amp Circuit Breaker at the power panel, set your meter to the 200 or 750 V AC setting and using one hand insert your meter leads into the left and right Neutral and Hot slots. Remember not to rest your opposite hand on the metal box, as that can cause a shock through your heart if something goes wrong. That’s why electricians traditionally stick their unused hand in a back pocket. It really doesn’t matter which side of the outlet gets the red or black meter lead since it’s Alternating Current.

Since the Neutral connection is at 0 Volts and the Hot connection should be around 120 volts, you should read somewhere between 115 and 125 volts on the meter display. If not, then something’s wrong with the power hookup. If you measure 0 volts, then maybe you need to reset the circuit breaker, or if you have an outlet with a GFCI (Ground Fault Circuit Interrupt) remember to push the little reset button on the outlet itself. If it still doesn’t measure 110 to 125 volts, immediately contact the stage manager. If you measure 220-250 volts, then that power outlet has been jury-rigged inside the circuit breaker box to produce higher voltage. This is illegal and highly dangerous as you’ll surely blow up every piece of electrical gear you plug into the outlet. So, if you read 240 volts on the 120-volt outlet do not plug in your amp, and, again, immediately contact the stage manager.

Hot to Ground

If hot-to-neutral checks out around 120 volts (110 to 125 volts), then it’s time to test the ground, so plug one meter lead into the HOT (shorter slot) and the other into the GROUND (U-shaped hole) connections.

Since you’re reading from the Ground connection, which should be 0 volts (less than 2 volts), and the Hot connection, which should be around 120 volts (110 to 125 volts), your meter should show about 120 volts.

If you read 0 or something strange such as 60 volts, then the ground wire might be floating, which could cause a hot-chassis condition that will shock you when touching the strings of your guitar and microphone.

Neutral to Ground

Next, check from Neutral to Ground. That should read very close to 0 volts, but up to 2 volts is acceptable according to the electrical code. If, however, you read around 120 volts from Neutral to Ground, then the polarity of the power outlet is reversed. Don’t plug in. Again, this can cause a dangerous hot-chassis condition depending on how your guitar or PA system is wired.

Final Exam

As a final check, a $5 outlet tester from your local home center will confirm that the polarity of the outlet is correct. Plug it into the power outlet on stage and you should see only the two yellow/amber lights light up. If you see any other combination, do not plug in your guitar amp.

Once you’re familiar with the procedures, all this can be done in a minute or two. It’s a very small inconvenience that will help ensure the safety of you and your band. Stay safe!

Quick Tips

Always set your meter to read AC volts using the 400-, 600- or 750-volt scale
Hot (short slot) to Neutral (tall slot) should read approx 120 volts (between 110 and 125 volts AC)
Hot (short slot) to Ground (U-shape) should read approx 120 volts (between 110 and 125 volts AC)
Ground (U-shape) to Neutral (tall slot) should read approx 0 volts (less than 2 volts AC)

Part 3 of this series will cover how to use a non-contact tester to check for dangerous voltages on a guitar or microphone.

Future Shock …

We’re looking for manufacturer or educational sponsorship to take the No~Shock~Zone back on the road. We’ve already presented six of these NSZ clinics in Washington DC, Houston, Dallas, Phoenix, Muncie and San Francisco. We would like to do more programs at colleges and selected retail stores across the country, but we need your support. Please contact hector@fitsandstarts.com or 732-741-1275 for sponsorship details. Your support could save lives.

RV Electrical Safety: Part VII – Wattage

Mike Sokol — Tue, 21 Sep 2010 23:52:58 +0000

The No~Shock~Zone: Part VII — Wattage

Understanding and Preventing RV Electrical Damage

If you’ve read the survey we did July 2010 in www.RVtravel.com, you know that 21% of RV owners who responded have been shocked by their vehicle. Review the 21% report at http://www.noshockzone.org/15/. What follows is #7 in a 12-part series about basic electricity for RV users and how to protect yourself and your family from shocks and possible electrocution. In addition, this series could protect your RV’s appliances, entertainment systems and computers from going up in smoke.

Watts Up?

Get to Work

We’re going to put voltage and current together and make them get to work. If you notice in the first illustration, there’s a lot of pressure at the bottom of the water tank. However, unless that pressure gets to move something, it simply sits there as stored energy just like the compressed air in a tank. Electricity works exactly the same way.

You’ll typically have around 120 volts of electrical pressure at an electrical outlet, but the air around the outlet has such high resistance to electrical flow, that the electrons just sit in the outlet waiting for a connection. So there’s no current flow unless you connect something that completes the circuit.

High Resistance to Flow

Here we’ve put a hole in the bottom of the tank connected to a pipe and see that water is flowing out under pressure. And you can imagine that flowing water could do useful work. It could turn a water wheel and make flour from wheat, it could drive a piston up and lift a heavy weight or it could even spin a turbine generator and actually make electricity.

If we put a small hole in our tank, there will be a high resistance to water flow and not much work will get done. That’s exactly what happens when you plug in an appliance that doesn’t draw much wattage, perhaps a 100-watt light bulb.

Low Resistance to Flow

But put in a larger hole and there will be a lot more water flowing since there will be less resistance to current flow. And, of course, all that extra current can be used to do even more work.

For instance, a 1,000-watt space heater needs 10 times the current flow of a 100-watt light bulb since it’s drawing 10 times more wattage, and that means 10 times the work is getting done.

So just like the difference between the stream of water from your faucet and the flow of water coming over Niagara Falls, more current and pressure equals more work getting done.

Wattage is Power

The same thing happens in your electrical outlet. Plug in an appliance with a high resistance to current flow (a small hole) and not much current will flow like the left side of the illustration.

The turbine won’t be spinning very fast and can’t do much work. However, plug in something with a low resistance (large hole) to current flow like the right side of the illustration, and a lot more current will flow. In this case the turbine will spin much faster and can do much more work.

That’s the basis of all electrical circuits, and how a power outlet “knows” how much wattage an appliance needs.

Appliances that need a small amount of power like a 100-watt light bulb will have a small electrical hole (with high resistance to flow), figuratively speaking, while other appliances like a 1,500-watt griddle that need much more power will have a larger electrical hole (with low resistance to flow). That built-in electrical resistance is part of the original design of the appliance, but that’s for a future article.

Inventor Alert

It takes voltage (electrical pressure) and amperage (electrical current flow) to get any work done. And that work is defined in a unit of measure called the Watt.

And like many cool discoveries are named after a famous scientist or inventor, in this case it’s named for James Watt, the inventor of the practical steam engine which started the industrial revolution. We’re not going to bore you will all the theory, but everything from horsepower to air conditioning BTUs to burning candles can be described in watts of power.

Basic Math

Here’s the basic formula, which we’ll also use later. Volts times Amps equals Watts (V x A = W). This formula implies that if your electrical outlet is putting out 120 volts and the appliance is drawing 10 amperes, that’s 1,200 watts of power that’s going somewhere. Again, we’ll use this simple formula later for some more calculations, but for now we’ll use it just once to calculate how much wattage (power) is available from 20, 30 and 50 amp campsite outlets.

20 amps times 120 volts equals 2,400 watts
30 amps times 120 volts equals 3,600 watts
50 amps times 240 volts equals 12,000 watts (6,000 watts per 120 volt leg)

That suggests that if you’re plugged into a 20-amp receptacle at a campsite, you can turn on up to 2,400 watts of appliances in your RV before you exceed 20 amps of current flow and trip the circuit breaker in the pedestal.

If you’re plugged into a 30-amp receptacle, you can turn on up to 3,600 watts of appliances before you trip the breaker.

And if you’re plugged into a 50-amp 120/240-volt receptacle, you can turn on up to 6,000 watts of appliances on each leg of your power system for a total of 12,000 watts.

How Much Wattage?

How do you know how much wattage each appliance needs? Well, there are at least two ways to find out. First, you can look at any appliance to find a wattage usage statement someplace on the back panel. For instance, a 1,200-watt hair dryer draws 1,200 watts. A 1,500-watt electric skillet draws 1,500 watts. Turn both on at the same time and it adds up to 2,700 watts. Now, if you’re plugged into a 20-amp outlet you’ve exceeded the 2,400-watt capacity of that circuit and you’ll trip the breaker in a few seconds. There’s a bit of a time delay that gives you a few seconds of grace before the breaker trips, but trip it will. Those same two appliances, however, would run successfully on a 30-amp outlet since that can provide 3,600 watts of power. And of course, a 50-amp 120/240-volt outlet can produce 6,000 watts per leg, so it would be just fine with a hair dryer and electric skillet at the same time.

Make a List

Jot down a list of everything you’ve got in your RV that’s electrical and find its current draw. A string of 20 Christmas lights with 7-watt bulbs will draw 20 times 7, which equals 140 watts. And a 1,000-watt slow-cooker might draw pretty close to 1,000 watts when on the high power setting, but much less when it’s turned to low simmer mode, maybe only 200 watts or so.

This all seems pretty simple until you start calculating wattage from non-heating appliances. A typical television might draw 100 watts of power, and that laptop computer might draw 50 watts from its power supply, which all seems simple enough. But motor-based appliances like your air conditioner or refrigerator will draw a peak of many times their rated wattage just to get things spinning inside. More on this in a later article, but that’s why generators are always more finicky about starting an RV air conditioner compared to an electrical outlet that’s connected to the power company. The circuit breaker in campsite pedestal is much more forgiving of a temporary overload, while a generator will try to protect itself and shut off the power if its peak wattage draw is exceeded for even a fraction of a second.

Measure It

The second way to find out how much current an appliance draws is to actually measure it. You can get a device called a Kill-A-Watt on Amazon for $25 that will allow you to plug in your appliances one at a time and actually measure how much wattage they’re drawing from the outlet. That’s also a good way to find out if your electrical conservation efforts are paying off by purchasing more “green” appliances.

And it will allow you to discover all sorts of things about lost power in appliances. For instance, a microwave rated for 700 Watts of cooking power (not the wattage usage number stated on the back panel) probably draws 1,000 watts or more from the power line. Where did those [additional] 300 watts of power go? Well, that discrepancy is due to the inefficiencies of the microwave generating process. So those other 300 watts turn into heat within the cabinet, which must be vented as warm air. You may not worry much about this until you find that those extra 300 watts put you over the edge and your trip a circuit breaker trying to run the 1,200-watt coffee pot and 700-watt (actually 1,000) microwave at the same time your refrigerator compressor kicks in.

And the big wattage item in any RV is the air conditioner, which draws a lot of peak amperage on startup. So when it all the currents add up beyond the capability of the circuit breaker and power cord, the circuit breaker trips and it’s lights out, literally.

How Much is Too Much?

A good rule of thumb is not to exceed around 85% of your wattage capacity simply by adding up the appliances you’ll turn on at the same time. So that means that a 20-amp receptacle that can produce 2,400 watts of power probably should not be used to draw more than 2,000 watts continuously. That adds some extra pad for appliances that need a little extra “kick” at startup.

The same rule applies to a 30-amp outlet that can produce 3,600 watts. Try not to run more than 3,000 watts of “planned” wattage and you probably won’t trip the incoming circuit breaker. And a 50-amp 120/240 receptacle has enough wattage to run a small house, which is exactly what you’re doing. They can easily handle 5,000 watts per leg without tripping.

Of course, some of you will want to squeeze every last watt out of the campsite pedestal, so in that case make sure you use a heavy enough extension cord that’s as short as possible from the RV to the campsite receptacle.

Breaker, Breaker…

What happens if you pull too much wattage from a campsite receptacle? Well, if you’ve sized your extension cord properly and the campsite has wired everything correctly, you’ll simply trip the circuit breaker. That’s exactly the job it’s supposed to do and nothing should be harmed from the shutdown.

However, if you have an air conditioner running at the time of power outage, know that they need around 2-1/2minutes for the compressor to lose its pressure and allow it to restart properly. So give things a few minutes to rest while you turn off your appliances. Then reset the circuit breaker by turning it all the way OFF first, then flipping it to the ON position. If it holds in the ON position properly, you probably just had a momentary overload. However, if you smell something burning or the circuit breaker trips off again immediately, stop what you’re doing and get an electrician to find out what’s wrong with your rig. Don’t keep flipping a breaker ON that keeps tripping OFF as there’s certainly something wrong that can cause additional electrical damage to your RV’s appliances if you keep applying power. We call that a “smoke test” and you really don’t want to go down that path.

Quick Tips

A 20-amp service can supply 2,400 watts
A 30-amp service can supply 3,600 watts
A 50-amp 120/240 service can supply 12,000 watts (6,000 watts per 120-Volt leg)
Plan not to exceed 85% of the receptacle wattage rating or you may get circuit breaker tripping
If you turn on a circuit breaker and it trips right away, contact an electrician immediately to find out the cause of the problem.

Future Shock

Part VIII of this series will cover GFCI (Ground Fault Circuit Interrupter) outlets and breakers, so stick around.

Feedback

RV Electrical Safety: Part VI – Voltage Drop

Mike Sokol — Sun, 12 Sep 2010 20:01:47 +0000

The No~Shock~Zone: Part VI – Voltage Drop

If you’ve read the survey we did July 2010 in www.RVtravel.com, you know that 21% of RV owners who responded have been shocked by their vehicle. Review the 21% report at http://www.noshockzone.org/15/. What follows is #6 in a 12-part series about basic electricity for RV users and how to protect yourself and your family from shocks and possible electrocution.

Rumors and Innuendo

We’ve all heard about how hooking up an RV on too long or too skinny of an extension cord can force its appliances to run on 100 volts instead of the regular 120 volts, thereby burning out the motors or other components. While this may happen only rarely in your home, that’s because the electric company works very hard to keep the voltage levels constant no matter how much current you’re drawing. However, that may not be the case when you’re using your own extension cord running from a campsite pedestal.

But before we get into the reality of what happens to electrical gear that’s running on 100 volts rather then a full 120 volts, let’s figure out why this voltage drop thing happens in the first place.

From the Beginning

We’re going to put together the concepts you’ve learned about voltage in Article I and amperage in Article V in this NSZ-RV series. If you’ve not read them already, then please start at the beginning and spend an hour reading parts I through V. [See http://www.noshockzone.org/category/rv-safety/ ] Consider this time an investment in your family’s safety. Even if you know how to run a digital voltmeter, please re-read Part II on meters since that’s important to your understanding of how current draw causes voltage drop.

What’s This Voltage Drop Thing?

If you look at the first illustration you’ll see a pump on your left that can supply 120 PSI (Pounds per Square Inch) of pressure, and two pipes heading to the right side. I’ve capped one pipe with a white stopper and the other with a black stopper so that no water can leak out. Because there’s no water flow, the pressure within each pipe will be equal to the pressure of the pump. The bottom pipe, which is hooked to the 120 PSI output of the pump, will have 120 PSI all along its length, while the top pipe, which drains back into the pump, will have 0 PSI along its entire length. And you can imagine that it really doesn’t matter if that pipe is large or small in diameter. The pressure within each pipe will be equal throughout its length. I’ve added a differential pressure gauge to the far right of the illustration that shows there’s now 120 PSI difference between the two pipes, just like a voltmeter reads the voltage difference between its two probes. Note that no real work is being done; it’s just an equalized pressure system. This is exactly what happens to an electrical outlet in your home or RV. There’s electrical pressure (Voltage) but no current flow (Amperage) until you plug something into it.

Big Pipes Equal Small Pressure Loss

Now let’s make our pump do some work. I’ve added a small turbine to the right side of the drawing connecting the top pipe to the bottom pipe. The pressure of the water will cause a current to flow through that small turbine to power your blender making a frozen drink of your choice. But this isn’t a perfect world, and because there are rough spots inside of those big pipes, they offer resistance to the flow. This shows up as a loss of pressure that’s dependent on how long the pipes are and how many gallons per minute we expect them to carry. In this case we have really big pipes carrying the water to the little turbine, so the small amount of flow (current) required only causes a 1 PSI drop in pressure in each pipe. So when we put our pressure meter across the ends of the pipes at the caps, you’ll see that instead of a full 120 PSI of pressure, we only have 118 PSI. That’s an acceptable loss in this case since our little turbine is rated for pressures from 110 to 125 PSI and all is well.

Small Pipes Equal Big Pressure Loss

Imagine, however, what would happen if your plumber went cheap and installed really small feeder pipes to your turbine. Your pump would still be creating 120 PSI of pressure, but the current flow would be restricted a lot by the too-small feeder pipes. Consequently, rather than losing just 1 PSI of pressure, you would now lose 10 PSI of pressure with the same current flow as before. Since the top of the turbine has 10 PSI of pressure holding it back, and the bottom of the turbine only has 110 PSI to begin with, there’s only 100 PSI difference in pressure to drive the little turbine. Our turbine needs at least 110 PSI to operate properly, so now it’s starved for pressure and won’t spin fast enough to do its job. This same effect of pressure loss would occur with larger pipes over very long distances. Therefore, if we made our pipes in the first illustration ten times longer, that 1 PSI of pressure loss would then become 10 PSI of pressure loss.

Big Wires

Now let’s substitute a battery or generator for the pump, and an electric heating element in our coffee maker for the turbine. Our generator is hooked up to the outlet powering the coffee maker’s resistive heating element with really big wires. And just as in the water example, there will be a certain amount of resistance to the current flow. This resistance to current (flow) is what causes voltage drops to occur. How much voltage drop is dependent on the type of metal inside the wire (typically copper, sometimes aluminum), the diameter of the wire (remember that 10-gauge wire is thicker than 14-gauge wire) and how long the run of wire happens to be (50 feet of wire will lose twice as much voltage as 25 feet of wire).

In our case we’ve run a sufficiently heavy wire from the generator to the outlet, so there’s maybe only 1 volt of electrical voltage (pressure) lost on the way through the black wire. But since it has to return through the white wire, there’s another 1 volt of loss on the return trip. That means the bottom side of the heater in our diagram is getting 119 volts of electrical pressure while the top side is getting 1 volt of electrical pressure. Since meters and heaters only care about the difference in voltage applied across their inputs, we’re providing 119 minus 1 which equals 118 volts. Since our little heater is rated for operation with voltages as low as 110 volts, we’re still in good shape and your coffee will be done in time.

Small Wires

But now we’ve cheaped out and installed far too skinny of an extension cord from the generator to the heater outlet. And any time we try to pull a significant current flow (let’s say, 10 amperes) down the skinny wire, there’s a lot of resistance to that flow, causing us to lose electrical pressure (voltage) just as we lost water pressure when using the pump with too-small of connecting pipes. In our generator illustration above there’s a 10-volt drop in the black wire and a matching 10-volt drop in the white wire. That leaves our heater with 110 volts on the bottom feed and 10 volts on the top feed. Again, our meter and heater element only care about the voltage differential applied to them, so it’s only working with 100 volts.

Bad Things

That should sound like a bad thing to you, and indeed it is. Two significant problems occur when you hook up your RV using a long or skinny (or both) extension cord. The first is that this “electrical friction” causing the voltage drop makes the wire itself heat up. And it can heat up to the point where it gets limp and catches on fire. The second problem is that your RV is only getting 100 volts of electrical voltage (pressure), when it really wants 120 volts. You can reverse think this and realize that voltage drops only occur when you’re drawing significant amperage like an air conditioner or microwave. So while your electronic appliances such as a television may be operating properly with nothing else running in your RV, as soon as you turn on that roof air conditioner, you might see your television’s electronics starve for voltage and shut down. That’s certainly a problem if you’re watching an NCIS marathon.

Truth or Fiction: Low Voltage Kills Appliances

Well, low voltage affects only certain kinds of appliances and only under certain conditions. Resistive heaters like a coffee pot really don’t care if you feed them 120 volts or 110 volts or even 100 volts. They’ll just happily draw less current, which makes less wattage, which then takes longer to bring your water to a boil. And certainly roof air conditioner compressors can refuse to start if you don’t provide them with sufficient voltage and current. That motor has to push a piston against a lot of Freon gas pressure, and if you don’t have enough push it’s going to stall. However, there is one type of electrical load that can be severely damaged by running off of too low a voltage, and that’s an AC-DC motor with brushes like in a circular saw.

Advanced Concept Alert

Here’s why…. AC-DC motors put out a reversed voltage (called Back EMF for Electro Magnetic Field) when running at their designed voltages. That’s because as these motors spin they also act as generators feeding a reversed voltage back into their own electrical circuit. And that reverse voltage (pressure) is what holds back the current flowing through their brushes (the sparky things you see at the back of your drill). However, if you starve an AC-DC motor for voltage by using too small or too long of an extension cord, they won’t develop enough of this internal reverse voltage to limit the current flow through their own brushes. And that’s why you see lots of sparks fly from your power tools when running them on too long and too skinny extension cords. Reducing the voltage on an AC-DC power tool motor actually increases its amperage draw. You’ll kill the brushes in short order and ruin the motor in your hand drill or circular saw unless you maintain full voltage to the tools no matter what your amperage load happens to be. Thick extension cords make for happy power tools.

Back to Basics

Also, of course, letting your voltage drop below 110 volts is bad for computers, sound systems and virtually everything else in your RV. And while it may not cause an actual meltdown in your stereo, it will reduce the performance of virtually everything not fed with sufficient voltage. Just like trying to start your car’s engine when the battery is nearly depleted will leave you with a grrrr, grrr, grrr and no start, making your appliances run from too low of a voltage, which will sometimes make them shut down or not boot up properly.

Replay

Go ahead and re-read NSZ part V on current flow and make sure you have a heavy enough extension cord for the job without getting a big voltage drop. If you’re in doubt, go one size heavier (lower gauge number) for the wire size, especially if you’re running more than 25 feet of total length. There’s really no such thing as too thick of an extension cord.

Quick Tips:

Long extension cords need to be heavier to reduce voltage drop.
Skinny extension cords have more voltage drop than thick extension cords.
Overloaded extension cords can overheat and catch fire.
Appliances generally don’t operate at full performance below 100 volts.

Future Shock

Part VII of this series will cover how to calculate current draw from the various appliances in your RV. Stick around.

Feedback

RV Electrical Safety: Part V – Amperage

Mike Sokol — Thu, 02 Sep 2010 22:40:58 +0000

The No~Shock~Zone: Part V -Amperage

Understanding and Preventing RV Electrical Damage

If you’ve read the survey we did July 2010 in www.RVtravel.com, you know that 21% of RV owners who responded have been shocked by their vehicle. Review the 21% report at http://www.noshockzone.org/15/. What follows is #5 in a 12-part series about basic electricity for RV users and how to protect yourself and your family from shocks and possible electrocution.

What’s an Ampere?

Besides being the name of the guy (Andre Ampere) who discovered that current flow caused electromagnetism, it’s the measure of how many electrons are flowing through a wire or conductor per second. For those who are counting that would be exactly 6.24151 × 1,000,000,000,000,000,000 (10 to the 18th power) electrons per second per ampere of current. However, the actual electron count isn’t important, so you can just think of it as gallons of electrons per minute, using our water tank model [illustrated in earlier articles in this series]. And, yes, we call this effect “current” both when talking about the flow of water in a river as well as the flow of electrons in a wire. Pretty cool, eh? It’s often abbreviated as “amps” and you’ll sometimes see it listed in milliamps (1/1,000 of an amp) on voltmeters. It takes 1,000 milliamps to equal 1 amp of current.

Pumps and Hoses

If you look at the illustration to the left, you’ll see a turbine pump pushing water counterclockwise around in a circle.

And depending on the pressure produced by the pump and the size of the water pipes connecting around in the circle, you’ll either pump a lot of Gallons Per Minute (GPM) or a few Gallons per minute.

In this case we’re using a pump that can produce 120 PSI (Pounds per Square Inch) of pressure to move water around a pathway or circuit. And because we have a large diameter pipe all around, this circuit can support a lot of current flow without losing much energy or pressure in the process.

Small Hoses

As you can see from the next illustration, if you use a very narrow pipe for part of this circuit, your gallons per minute (GPM) flow will be very low.

So if you have a pump that might be able to push 10 Gallons Per Minute through a big pipe, it could be restricted to perhaps 1 GPM flow if you use too narrow of a pipe for any part of the circuit.

And just like the garden hose you use to water the plants in the back yard, it won’t be able to deliver enough water flow if it’s too small in diameter or too long in length.

The exact same thing happens to electricity as it flows through a wire like an extension cord. Just like pipes, thick extension cords can support lots of current flow, while skinny extension cords can only support a small current flow.

Big Wires

Take a look at the illustration of the electrical circuit on the left. Instead of a pump let’s substitute a battery or AC generator, and instead of a pipe let’s use a wire going around in a circle, which we’ll call a circuit (just like a horse racing circuit).

If the wire being used is large enough in diameter, then the generator or battery can push the full 10 amperes around through the circuit without any loss, which is the typical amount of current your coffee pot might require to heat up water.

And as long as you don’t try to push more amperes of current through a wire than its rated for, then all should be fine.

Little Wires

However, the exact same generator or battery could be in trouble when attempting to push those 10 amperes of current through a skinny wire or extension cord. Now your generator might only be able to push 2 amps of current through the circuit since there’s so much resistance to flow built into the smaller wires (think pipes).

And while you will certainly notice a significant drop in water flow from your garden hose if it’s a bit too skinny for the job, you may not notice the problem you’ll have from a small extension cord when it’s supporting a lot of current flow. And that can cause all sorts of problems with your RV.

That’s because, instead of just restricting the water flow in a hose, electrical wires can heat up to the point of catching on fire if you try to push more current through them than they’re rated for. Ever lay your hand on an extension cord and felt it was hot? That’s the problem with too much current, it causes heat. How much current is OK to run through an extension cord? Well, glad you asked.

Size Me Up

For those of you unfamiliar with extension cord and wire specifications, the lower the number of the gauge, the thicker the wire and the more current (amperage) that can flow through it without overheating. Sort of like shotgun gauges.

For example, a 14-gauge extension cord might be rated for only 15 amperes of current flow, while a 10-gauge extension cord could be rated for 30 amperes of current, depending on total length of the cable and type of insulation. And if you exceed the rated amperage capacity of an extension cord, then you’re asking for trouble.

(FYI: If you want a gauge tester for yourself, you’ll need to order one from Amazon for $19 since the big box stores won’t know what you’re talking about. Here’s what I use: Just search on Amazon for – General Tools 20 American Standard Wire Round Gauge )

Flow Capacity

More on this in a future article, but here’s the basic AC amperage capacities of AWG [American Wire Gauge; standardized U.S. wire gauge system] standard wire sizes. As you can see from the chart, the lower the gauge, the larger the diameter of the wire and the more current it can carry without overheating. Also, it’s often noted that you should make the wire one size larger than called for in the chart if you’ll be running a long distance. NOTE: 50 or 100 ft of extension cord from the campsite pedestal to your RV is a very long distance. Do not expect a 12-gauge extension cord to carry a full 20 amps of current over 50 feet or more. In that case, go to a 10-gauge cable to handle the current over that distance. And you can see that if you want to hookup to a 240-volt receptacle with a 50 amp circuit breaker, you’ll need a 6-gauge extension cord if you’ll be drawing current from the outlet at maximum capacity. And you know you will because RVs are power hungry with microwaves, air conditioners, flat screen televisions, coffee makers, and all sorts of other electrical appliances. Using a cable with sufficient amperage capacity will also minimize your voltage drop which can cause some electronic devices to misbehave.

Did I say “voltage drop”? I’m sure you’ve heard of it, but how many of you know what it really means? Well, that sounds like a good subject for the next article. So stick around while we continue learing about RV electricity and how to stay safe while using it. See you all next week.

Quick Tips

Extension cords can heat up and catch on fire if you exceed their amperage rating by drawing too much current.
The lower the gauge number (AWG) on an extension cord or wire, the more current it can safely carry without overheating.
Electricity needs a complete circuit for current to flow from the high voltage side to the low voltage side of the generator or battery. That current is measured in amperes.

Future Shock

Part VI of this series will cover how amperage draw causes voltage drop, which is why your coffee pot can cause your lights to dim in your RV. Stay tuned.

Feedback

After you’ve read this article, please leave us any comments or suggestions for future topics. We’d love to know how we’re doing with this important project. And while you’re at it visit www.RVtravel.com for all things related to RV travel and lifestyle.

Mike Sokol is the chief instructor for the HOW-TO Sound Workshops (www.howtosound.com) and the HOW-TO Church Sound Workshops. He is also an electrical and professional sound expert with 40 years in the industry. Visit www.NoShockZone.org for more electrical safety tips for both RVers and musicians. Contact him at mike@noshockzone.org.

RV Electrical Safety: Part IV – Hot Skin

Mike Sokol — Wed, 25 Aug 2010 12:51:24 +0000

The No~Shock~Zone: Part IV – Hot Skin

Understanding and Preventing RV Electrical Damage

If you’ve read the survey we did July 2010 in www.RVtravel.com, you know that 21% of RV owners who responded have been shocked by their vehicle. Review the 21% report at http://www.noshockzone.org/15/. What follows is #4 in a 12-part series about basic electricity for RV users and how to protect yourself and your family from shocks and possible electrocution.

The Big Picture

If you’ve been diligently reading this series, you should at this juncture understand the basic concepts of what voltage is, how to read it with a meter and how to check the polarity of a campsite power outlet. If not, then go back and review parts I, II and III on RV electrical safety.

But why is this concept of voltage and polarity so important? Well, one of the greatest dangers of RVing, perhaps second only to a fire (which is really terrifying) is getting shocked and possibly electrocuted when touching the skin of your RV. And while some campers may have been injured by a bare wire on an extension cord or while poking their fingers in a power panel without proper precautions, the majority of RV shocks come when you least expect them, from the skin of your RV while simply opening the door.

Hot Skin

An RV Hot-Skin condition occurs when the frame of the vehicle is no longer at the same voltage potential as the earth around it. This is usually due to an improper power plug connection at a campsite or garage AC outlet. Now to be honest, I think the majority of campgrounds have properly wired and maintained power pedestals, but certainly there are instances where a campsite has outlets with reversed polarity or without proper grounding at all. But I’ve seen enough “rewiring” jobs to know that RV owners are also to blame for improper wiring of their own extension cords and 30-amp adapters.

The scenario could go something like this: You plug your RV plug into a loose or worn campsite power outlet. Everything seems fine until you crank up your air conditioner and turn on your coffee maker. That’s when you notice the smell of burning plastic and find that the male plug on your RV extension cord has melted down due to all that current going through a loose connection. Rather than throw that expensive extension cord away, you go to your local big box store and buy a new power plug. However, when you take the wires off of the old plug there’s no diagram to show you how to connect the new plug properly. If you guess right while putting on a new plug, then all is well. If you guess wrong, then you’ve reversed the polarity of your incoming AC power. After that it just takes the right combination of circumstances such as a rainstorm to wet the ground in front of your RV, and you touching the screen door with a damp hand while standing outside. That’s when you can get shocked or even electrocuted. The severity of the shock can vary from a mild tingle to stopping your heart, depending on how wet you and the ground are and the voltage of your RV skin. But make no mistake, rather than the 30 or 40 volts of a high-resistance tingle, it’s possible to have the skin of your RV go to 120 volts with full current of the campsite pedestal with 20, 30 or even 50 amps available.

Insulation

The reason we don’t notice this Hot-Skin condition until it’s too late is that an RV is basically a big metal frame sitting on rubber tires. And those tires act as electrical insulators just like the rubber surrounding the metal wire of your extension cord. That means that the skin of your RV can be electrically charged with 30, 60 or even 120 Volts with no visual indication of the problem until you complete the connection to the earth with your hand. Then because your own body provides a low resistance path to earth (remember the pipes between the water tanks in Part I of this series), current will flow through you to the ground. How much current is really the subject of another article, but if your hands and feet are wet your body becomes a 1,000-Ohm resistor connected from your hand on the doorknob to your feet on the ground. This will allow over 100 mA (milliamperes) of electrical current to flow through your heart. Tests have shown that as little as 5 mA of a 60-Hz current (what comes out of your electrical outlet) can cause your heart to go into fibrillation (essentially a heart attack). So you can easily get 20 times the current needed to kill yourself from a 120-volt outlet. Note that 100 milliamps of current isn’t enough to trip a standard 20- or 30-amp circuit breaker, but it’s supposed to trip a GFCI (Ground Fault Circuit Interrupt) as long as it’s been properly connected. But don’t risk your life on untested technology — check for Hot-Skin conditions before you get shocked.

Making a list, checking it twice….

What follows are two ways to determine if the skin of your RV has been electrified. One method involves using a voltmeter just like we learned about in Part II of this series, while the second method uses a non-contact AC tester like you see electricians use to check for live outlets. Both methods are described below. But be aware that even if you tested your RV when you made camp and found it safe from a Hot Skin condition, that could change at any time if something happens to the campsite power after you’ve plugged in. If you feel even the slightest tingle from your RV, that’s the time to shut off the circuit breaker from the campsite power and get an electrician to double-check the outlet ground and polarity. Don’t bet your life on a faulty connection.

Using a Meter

After you’ve tested the campsite outlet for proper polarity (Part III of this series), powered off the circuit breaker and connected your RV power plug, now is the time to turn the circuit breaker back on and confirm that your RV is safe from a Hot-Skin voltage.

To use a standard digital voltmeter such as the one we learned about in Part II of this series, you’ll need to set it to measure AC voltage. Note that since a Hot-Skin condition will typically be less than 120 volts, the 200 volt or 750 volt AC setting [as pictured] will be fine.

Just like before, plug the black probe into the black COM connection on the meter and the red probe into the RED VOLTS connection on the meter. Remember, never plug into the 10 Amp connection, and never set the meter dial to amps or ohms. That’s for advanced testing only, and you’ll only blow out the meter’s fuse if you try to test for voltage that way.

Ready… Set… Test….

If you’re close enough to any metal going into the earth, such as the exterior of the pedestal power box or a metal water pipe, poke it firmly with the sharp tip of the black probe. You’ll need to punch through any rust or paint, so an exterior bolt or machine screw is usually a good choice. Now without touching the body of your RV with your hand poke the skin of your RV with the sharp tip of the red probe. Again, this needs to make connection to the metal skin of your RV, so if you want to avoid making little holes in your paint job pick a spot like the trailer hitch or a chrome door knob.

Next, while both probes are making contact you should read very close to 0 (Zero) volts. The National Electrical Code allows up to 2 volts on the ground, so 1 to 2 volts is safe. If, however, you read 10 volts, 50 volts or 120 volts, that’s the time to back away from the RV, turn off the circuit breaker, pull the power plug and immediately get the campsite electrician to find out what’s wrong. If he tells you that 50 volts on the skin of your RV is fine, demand your money back, break camp and get out of there. Do not let your family or pets enter an RV with a Hot Skin condition. Also, it’s a good idea to alert your local RV association that a campground has a dangerous power condition. That way you help the next RVer, too.

Using a Non-Contact Tester

While a digital voltmeter is the gold standard method for testing Hot Skin conditions, it must be used exactly right or it can give you a false sense of security. Therefore, perhaps the easiest and best way to check for an RV Hot Skin is by using a $30 non-contact AC tester such as a Fluke VoltAlert. These testers look like a fat pen with a plastic tip and are available at hardware stores such as Sears or Lowes. Most have a blinking light and beeper that makes noise when the tip is held near an energized circuit. How do I know these things work? Well, I built a Hot Skin simulator that can energize the body of an RV with any voltage from zero to 120 volts at the twist of a dial. I’ve energized everything from a microphone to an Airstream to find the best Hot-Skin testing methods. Yes, it’s a bit Frankenstein, but this gear allows me to see how well the various test methods work. And the Fluke VoltAlert seems to work very well for Hot-Skin conditions as low as 40 volts.

To test for an RV Hot Skin just turn on the non-contact tester by pushing the power button quickly, which will begin to blink once every few seconds to show you it’s on. Then confirm the tester is working properly by poking it into a hot blade of the power outlet on the pedestal. It should beep at you and blink if all is well. Now, gripping the tester firmly in one hand while standing on the ground, move the plastic tip until it’s touching anything metal around your RV. This could be an aluminum screen door, the exterior of an Airstream or the steel of the trailer hitch. With a non-contact tester you do not have to punch through the layer of paint, rust or plastic. If your RV has more than 40 volts on the skin, the VoltAltert will light up and start beeping at you, even from an inch or more away from the surface of the RV.

Caveats

Now, here are a couple of warnings about using non-contact testers to check for Hot-Skin conditions. 1) These testers need to have your hand wrapped around them to sense the earth ground; so if you hold them with just the tips of your fingers it’s possible to get a false-safe reading. 2) Non-contact testers need your feet to be near the ground to know the actual earth potential, so if you’re standing on a fiberglass ladder they won’t read properly. Additionally, since non-contact testers are looking for the voltage difference between the your hand and the plastic tip of the probe, if you’re standing inside an RV with a Hot Skin and you test your galley sink, they won’t indicate trouble when indeed there is. Therefore, always grip the non-contact tester firmly in your hand while standing on the ground outside your RV. And if your vehicle has as little as 40 volts of Hot Skin potential, the tester should alert you of the danger even without physically touching your RV. You can just slip your VoltAlert pen in your pocket and use it to quickly test any RV in the campground you might be visiting. It only takes a few seconds to test for a Hot-Skin problem this way, and you may save another RV owner’s life.

Outlets Re-visited

Since these non-contact testers are designed to check outlets for electrical power, they’re also a great way to confirm outlet polarity. If you remember what a typical AC outlet looks like, you can poke the VoltAlert into the tall neutral slot (no blink or beep), then the ground hole (no blink or beep) and finally the shorter hot slot (should blink and beep). It won’t tell you the exact voltage of the outlet like a voltmeter, but it will confirm if the polarity is correct and tell you if the ground connection has been floated and electrified by another RV with a short in its own wiring. This is pretty cheap insurance since you can never be too safe around electricity.

Quick Tips

Do the Hot-Skin test after you’ve checked campsite outlet polarity and voltages with a volt meter.
Perform a Hot-Skin test every time you plug into a new campsite or home power outlet.
If you ever feel the slightest tingle or shock from your RV, avoid all contact, shut off the AC power at the pedestal, and get professional help to determine the cause of the shock.
Even if you’ve stopped getting shocked from your RV because the ground is dry, the Hot-Skin problem has not fixed itself.
Be sure to properly maintain your RV electrical system and test all RV interior outlets for proper polarity and grounding.

Future Shock

Part V of this series will cover amperage and ways to calculate how much your RV needs BEFORE you plug into a power pedestal, so stay tuned.

Feedback

After you’ve read this article at www.RVtravel.com, take a trip over to www.NoShockZone.org and send us your comments and suggestions. We love to know how we’re doing with this important project.

Mike Sokol is the chief instructor for the HOW-TO Sound Workshops (www.howtosound.com) and the HOW-TO Church Sound Workshops. He is also an electrical and professional sound expert with 40 years in the industry. Visit www.NoShockZone.org for more electrical safety tips for both RVers and musicians. Contact him at mike@noshockzone.org.

No~Shock~Zone

RV Electrical Safety: Surge Strips

RV Electrical Safety: Part XI — Extension Cords

The No~Shock~Zone: Part XI — Extension Cord Testing

Understanding and Preventing RV Electrical Damage

The Lowly Extension Cord

The Ends

Exploratory Surgery

White is Neutral

Green is Ground

Black is Hot

Measurements

Hot Test

Neutral Test

Ground Test

Color Code

Wrap Up

You Get What You Pay For

Future Shock

Feedback

RV Electrical Safety: Part X – GFCI Testing

The No~Shock~Zone: Part X — GFCI Testing

Understanding and Preventing RV Electrical Damage

GFCI review

It’s All About Balance

Nuisance Tripping

Less Than Perfect?

Charting Fault Combinations

Measure It

Wrap Up

Future Shock

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RV Electrical Safety Part IX – In Review

No Shock Zone RV in Review

NSZ-RV Review

RV Electrical Safety: Part VIII – GFCI

RV Electrical Safety: Part VII – Wattage

RV Electrical Safety: Part VI – Voltage Drop

RV Electrical Safety: Part V – Amperage

RV Electrical Safety: Part IV – Hot Skin

RV Electrical Safety: Part III – Outlets

RV Electrical Safety: Part II – Meters

RV Electrical Safety: Part I – Volts

The Shocking Truth About RV’s

RV Electrical Safety: Part VIII – GFCI Theory

The No~Shock~Zone: Part VIII — GFCI Theory

Understanding and Preventing RV Electrical Damage

GFCI?

Why Do We Need a GFCI?

How Does a GFCI Work?

Keeping in Balance

Out of Balance

Teeter Totter

Putting It All Together

Future Shock

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Stage Electrical Safety – Part II: Meters

The No~Shock~Zone

Stopping Hums, Buzzes and Shocks on Stage Part II: Meters

Just the Facts

Shake & Bake

The Meter

The Outlet

Generator and Distro Power

The Measurements

Hot to Neutral

Hot to Ground

Neutral to Ground

Final Exam

Quick Tips

Future Shock …

RV Electrical Safety: Part VII – Wattage

The No~Shock~Zone: Part VII — Wattage

Understanding and Preventing RV Electrical Damage

Watts Up?

Get to Work

High Resistance to Flow

Low Resistance to Flow

Wattage is Power

Inventor Alert

Stopping Hums, Buzzes and Shocks on Stage
Part II: Meters

Understanding and Preventing RV Electrical Damage
Copyright Mike Sokol 2010 – All Rights Reserved