RV Electrical Safety: Part XI — Extension Cords

Nov 9th, 2010 | By | Category: RV Safety

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

Understanding and Preventing RV Electrical Damage

Copyright Mike Sokol 2010 – All Rights Reserved   

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://new.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.

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. 

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.


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.


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.

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.  

11 Comments to “RV Electrical Safety: Part XI — Extension Cords”

  1. Jonathan Johnson says:

    How do you know that? (You said to ask….)

    • Mike Sokol says:

      Well, I’ve run sound at a number of concerts where light-duty extension cords were used for big PA amplifiers, and I’ve seen them get so hot that you can’t touch the extension cords with your hand. Also, lighting systems using too-small extension cords have caught on fire right above me head which isn’t too fun. I’ve also seen a number of electric heaters on extension cords that have caused power outlets to overheat and catch on fire. For instance, a good friend of mine lost his guitar-shop when an electric space heater overheated an extension cord which melted and sparked a fire.

  2. When you say:

    “The orange molded extension cords you get from the big box stores are usually not heavy enough for rugged RV usage…”

    Are you referring to the typical 12 and 14 gauge cords? The reason I ask is that I’ve seen orange molded cords that use 10 gauge conductors (but they aren’t common).

    • Mike Sokol says:

      I’m referring to the 14 ga and 16 ga 50 ft extension cords you can get for $5 to $10 at Lowes or Home Depot. Those are just plain deadly for an RV. But I see people hookup their RVs with those all the time.

      I think that for most cases, a good 25 ft molded cord that’s 10 gauge would be the best solution, since even if you’re only using for a 20 amp RV service it minimizes the voltage drop. Campgrounds are generally on the low voltage side of things to begin with, so why throw away any more volts than you need to?


  3. Bill Knight, CBET says:

    In my 28 years as a Biomedical Equipment technician at a major University Medical Center, I repaired hundreds of power cord plug/cable connections due to abuse or their failing the annual electrical safety inspections. When i started in the early 1980’s it was common to find the wires tinned (coated with solder) where they attached to the plug screws. It was found that tinned wires were associated with the plug wire connection screws coming loose and arcing of the power connections or poor grounding resulting. That practice was banned. I was also taught a good practice (not written in any code) of adding an extra 3/4 inch of wire length to the grounding (green) wire attaching to the plug. The rationale was that if the cable jacket was pulled on (like someone rolling a defibrillator cart to a resuscitation code and not unplugging the defibrillator from the wall) the internal conductors feeling the strain would be the hot or neutral, but the extra length safety protective ground wire would be last to break. This mirrors the longer length idea of the ground pin on male NEMA 5-15P plugs. Your photos of internal plug wiring did not reflect this wiring improvement.
    BTW, at the end of my career, internally soldered, injection molded, hospital grade power cables became the norm, which were more rugged, and had less labor and overall cost than the old cable/screw-on plug assemblies.

    • Mike Sokol says:

      Probably a good idea to make the ground wire a little longer. And that’s the reverse of how audio cable are wired since the shield is so much heavier than the little 22 gauge signal wires. However, due to the fact that RV extension and shore power cords are exposed to rain and moisture, only pre-assembled molded AC connectors are approved for RV use by the NEC.

  4. Bill Knight, CBET says:

    Another comment on RV extention cords:
    WalMart (and camping supply stores) stock a 30 amp RV extention cord , with appropriate wire guage. A 30 amp to 15 amp RV adapter can be put on the plug end to connect to a household outlet.

  5. Chris Driscoll says:

    Had a strange experience. Arrived at site plugged in using 50a extension and 50a to 30a converter…both brand new. All ok overnight and in the morning. Once it got warmer, neighbors turned on their fans and some AC. My hardwired power system started shutting off and turning on power signalling a ground fault. Happened over and over. Eventually turned breaker off. Turned it back on around 530 and same thing. Waited until 7 730 then all was fine again…
    I had virtually no power draw. Power center showed I was pulling 2 amps. I didnt have lights or AC on at all.

    Thought maybe my extension cord or converter pigtail was the cause but wouldn’t it happen all the time?

    Am assuming it was an issue at the CG pedestal but wouldnt that happen all the time too if there was CG power issue? Can a ground fault occur in CG wiring only when the load increases?

    Any thoughts?

    • Mike Sokol says:

      I believe you’re experiencing an interesting phenomenon I’ve named a reflected hot skin condition. This occurs at a campground where there’s the loss of a EGC Ground Connection between one of the pedestals in a loop and the service entrance box ground-bonding point. If any other RV in that loop has any ground leakage from a line-to-chassis fault, then their own RV as well as ALL other RVs in that loop will have their ground voltages elevated as well, creating a hot-skin condition on multiple RVs from their pedestals.

      The dangerous thing is that this hot-skin voltage can go all the way up to 120 volts with potentially deadly currents that can electrocute anyone who touches the RV and the wet ground at the same time. So the campground needs to immediately have all their pedestals checked for ground continuity using something called a Ground Impedance Tester, such as an Amprobe INSP-3 or Ideal SureTest Analyzer. Please have the campground manager contact me for details before someone gets injured or killed.

  6. George B. says:

    Mike, thank you for all of your professional knowledge and parting it with us “Happy Campers”. I look foreword to many more RV electrical safety articles and video’s coming from you. You are a blessing! Psalm 34-17.

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