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.
I’ve been teaching RVelectricity seminars all week at the Hershey RV Show, and will cover one question that came up several times over the course of 3 days.
We see that you’re using a Non-Contact Voltage Tester to check for hot-skin voltage on an RV, but why are you using one that’s rated for 100 to 600 volts, and yet you say it will find a hot skin as low as 40 volts. Is that true? If so, why?
Great question. As you saw in my seminar using a tiny model VW Microbus, a NCVT (Non-Contact Voltage Tester) rated for a low of 100 volts will trigger on a hot skin as little as 40 volts. And an 80-volt hot skin will trigger from 2 inches away, with a 120-volt hot skin triggering from 4 or more inches away.
And if I had a full-size RV those ranges would be extended up to 2 feet or more for a 120-volt hot skin. That’s because the size of the electrical field created by a large electrified object reaches out further to energize the capacitive sensor in the NCVT. The 100-volt lower limit for this tester is for when it’s checking something really small, like the single electrical wire it was originally designed for. But since we’re using it on a really large electrified object (your RV), its sensitivity is amplified simply due to the huge surface area that has a hot-skin voltage.
So most any Non-Contact Voltage Tester that’s rated for a low range of 40 volts to 100 volts and a high range of 600 to 1,000 volts will find an RV hot-skin condition as low as 40 volts when you make contact with the tip, and will probably find a 120-volt hot-skin RV from 2 feet away. Make sense?
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 40+ 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.