Mis-wiring a 120-volt RV outlet with 240-voltsApr 1st, 2013 | By Mike Sokol | Category: RV Safety
Mis-wiring a 120-volt RV outlet with 240-volts
I’ve been answering a lot of forum questions lately from RV owners who paid an electrician to install a 30-amp/120-volt TT-30 RV outlet for powering their RV in the driveway. But the electrician somehow gets the wiring wrong and connects 240-volts to their 30-amp RV outlet rather than 120-volts. Of course, plugging your 120-volt RV into an outlet mis-wired with 240-volts will destroy just about every electrical appliance, converter, inverter, and electronic gadget in your RV in a matter of seconds.
So why does this happen? Don’t electricians know better? Well, they should be reading the markings on outlet itself for the proper voltage, but it’s typically in very small black-on-black writing. I think the real cause of this costly mistake is that a 30-amp/120-volt RV outlet closely resembles a 30-amp/240-volt Dryer outlet. If you look closely at the pictures you’ll see that the 120-volt RV outlet has a U-shaped ground contact, while the 240-volt Dryer outlet has an L-shaped ground/neutral contact. That’s right… 30-amp Dryer outlets often have a missing safety ground, depending on the Neutral wire to properly ground your appliance. And yes, that’s still code compliant in older installations.
So unless you specifically hand your electrician a wiring diagram and check his work after completion, you could be taking a big risk. I’ve created a graphic of just how similar these two very different electrical outlets look, and the proper wiring hookups for each one. Please print out this diagram and hand it to your electrician. If he or she doesn’t seem to understand the difference, then you need to get a new electrician.
Finally, test the outlet yourself for proper voltage before plugging in. Here’s how your meter should read on a correctly wired 20 or 30 amp / 120-volt outlet.