Friday, December 9, 2022


RVelectricity™ – What you missed about electrical troubleshooting last week…


Dear Readers,
If you’re one of the 400+ viewers of the Ask the Expert webcast interview I did with Mike Zimmerman last week, thanks for sticking around. If not, here are a few of the things that Mike Z and I discussed over the hour-long webcast about electrical troubleshooting. You can watch the full video interview and learn how to do all these things HERE.

The Red Shirt Society

After you’ve been doing electrical power and control for 50 years, you get to wear a red shirt. At least that’s what I’m telling myself.

I’ve been doing serious electrical work for 50 years and Mike Z has 45 years in the business. While I’m more of an industrial power and controls guy, and Mike Z is more of a power distribution and code guy, we both break down electrical troubleshooting much the same way. We divide the problem into small chunks you can measure and understand.

Get thee to a meter (and learn how to use it)

Don’t waste your money on expensive meters with all kinds of extra functions you’ll never use, and which will confuse your basic testing. You can get a good manual digital multi-meter for less than $30, and an AC/DC clamp meter for less than $75. Here’s a nice digital multi-meter (DMM) from Klein that’s available in many big-box stores or on Amazon HERE.

Clamp It…

In the webcast I showed how to use a basic AC/DC clamp meter to measure if a fuse was blown using the continuity (beep) test. Yes, this type of meter can measure AC or DC volts, AC or DC amps, continuity, temperature and capacitance. Oh yes, it also includes a NCVT function, so what’s not to like?

I often say that if I could only take one meter with me on a gig it would be an AC/DC True-RMS clamp-meter. I can measure practically anything I want with it, and then hang it on my belt loop to free up my hands. The model of the clamp-meter I used in the webcast was a Southwire 21550T which you can find on Amazon HERE.

Remember that for much of what you do in RV electrical troubleshooting (like measuring a fuse or bulb), a continuity test is the simplest way to determine if things are working. For more advanced troubleshooting, you can also use an AC/DC clamp meter to measure AC and DC voltage, or AC and DC current.

Testing for EGC (ground wire) bond to the RV frame

Mike Z also went into detail about how to use the continuity test on the meter to test that the shore power ground conductor is properly bonded to the RV frame.

That showed up in a troubleshooting session he did over the phone just last week, where a single RV was causing a hot-skin voltage to appear in multiple RVs at the same campground.

In a nutshell, if the ground-to-chassis connection of your shore power cord fails (measures no continuity), then there’s no place for any fault or leakage current in your RV to go, and it just turns into a hot-skin voltage.

How to measure a pedestal with a multi-meter

While EMS/Advanced Surge Protectors are great safety devices, you can discover a lot more problems by metering a pedestal with a volt-meter. Here’s a screen shot of me using a 30-to15-amp adapter plug to make measurements easier.

What about 50-amp / 240-volt service?

Here’s one of my basic receptacle diagrams of how a properly wired 50-amp pedestal should measure. Yes, it’s exactly like the split-phase power feeding your bricks-and-sticks house.

Be aware that it’s extremely important that you measure either a nominal 208 volts or 240 volts between L1 and L2 on the 50-amp outlet. If it measures 0 volts, then the campground has created a bootleg split-phase connection, and you’ll probably burn up your neutral wiring inside of your shore power cord, transfer switch, or load center.

Yes, I take requests…

I’m already planning on doing a discussion of my Hughes AutoFormer testing next month. But after that you all get to choose.

That could be a person you think would be a great interview (No, I can’t promise Elon Musk or Billy Joel), or a topic you would like covered (I’m working on more EMS/Advanced Surge Protector demonstrations), or practically anything else you can think of. Just make your requests on my new RVelectricity forum or, if you’d rather, in the comments below and let me see what could work.

Let’s play safe out there….

Send your questions to me at my new RVelectricity forum here.

Mike Sokol is an electrical and professional sound expert with 50+ years in the industry. His excellent book RV Electrical Safety is available at For more info on Mike’s qualifications as an electrical expert, click here.

For information on how to support RVelectricity and No~Shock~Zone articles, seminars and videos, please click the I Like Mike Campaign.



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11 months ago

Why do 50-amp EMS manufacturers choose to cut off both power legs (L1 and L2) when only one is experiencing a low voltage condition? I get the “It would take two contactors” but really? They’re not THAT expensive and cutting off only the low leg would not make it dark, quiet and HOT inside an RV that may have a pet alone inside.

If there really were 240 VAC appliances or equipment in an RV then yes, both legs would have to be cut but perhaps cutting one leg could be an optional jumper setting like the time delay for air conditioner compressors is on some units.

Is it because the 50-amp breaker has to be dual-ganged as does the main breaker in the RV, making this an electrical code issue because it’s a circuit interruption device?

Or what? Do you have any idea not related to cost?

Mike Sokol
11 months ago
Reply to  J J

Please pose this question on my RVelectricity forum at: