RV Electricity – Just Ask Mike (J.A.M.): Pedestal readings for 50-, 30- and 20-amp outlets

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By Mike Sokol

Welcome to my J.A.M. (Just Ask Mike) Session, a weekly column where I answer your basic electrical questions. If you’re a newbie who’s never plugged in a shore power cord (or ask – what’s a shore power cord?), or wonder why your daughter’s hair dryer keeps tripping the circuit breaker, this column is for you. Send your questions to Mike Sokol at mike (at) noshockzone.org with the subject line – JAM.


Dear Mike,
Do you have a single page showing the voltages of all the outlets on a pedestal? Maybe something we could print out for reference? —Mac (the knife)

Dear Mac,
Here you go. Note that a 50-amp RV outlet needs to measure either a nominal 240 volts from Hot-1 to Hot-2 (plus or minus 20 volts) or 208 volts (plus or minus 16 volts) from Hot-1 to Hot-2, but NEVER 0 volts from Hot-1 to Hot-2, as that shows the pedestal has been miswired as a single-pole/240-volt service, which will burn up your neutral wiring.

And in all home and campground circuits it’s normal to measure at least 1 to 3 volts between the neutral and ground contacts. That’s not a ghost voltage at all. It’s the expected voltage drop you’ll find on any branch or feeder circuit that’s carrying a load. In fact, you could measure up to 5 volts between neutral and ground and I wouldn’t worry about it. But anything over 10 volts should NEVER happen, so if that happens it’s time to troubleshoot the loss of the EGC ground immediately.

I’ve also included a page-size PDF you can download and print out by clicking on this link: pedestal_metering_all_outlets

Happy measuring…

OK, everyone. Remember that electricity is a useful and powerful force, so we all need to pay attention to safety precautions while using it.

Let’s play safe out there….

 

 

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

Hi Mike,

I find your article very informative. I wanted to ask you about laying out a small RV park.

I would like to run 3 camper slots. Each will have its own pedestal (50, 30, 20 amp (110)).

These will be 125 amp Metered 120/240 VAC Mil Bank Works meter.

The power company will put me a 200amp or 400amp service at my choice.

Do I need to run 200 or 400 amp service?

For the Main breaker do I need to run a 200 or 225 amp outside panel?
Or do I need to run something different?

Since they will only be using either a 50 amp or 30 amp only not both.

Your thoughts and opinions is very appreciative.

John

Andy Hughes
2 months ago

Thank you Mike.

tom
3 months ago

Another excellent tip from Mike.