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. This week I discuss adapters and why you shouldn’t plug a 20-amp cord into a 50-amp outlet.
I’ve got a cargo van camper conversion. I just need to plug into a 15- or 20-amp 120-volt socket with my extension cord. Can I use the first adapter to connect to 30-amp and/or connect both adapters in line to plug into a 50-amp socket? Thanks. —Jim
Thanks for the picture of your proposed hookup. And thanks for checking with my RVelectricity Facebook group first. There were a lot of good answers there why this isn’t a good idea. I’ll also cover it in my JAM session so it will reach even more readers.
Every picture tells a story…
As we can see, there’s a 50-to-30 amp dogbone adapter, plus a 30-to-20 amp puck adapter connecting to a standard 15-amp extension cord. Looks like it should work, right? And technically it does work, since the 50/30 adapter will properly connect one of the 120-volt hot legs of the split-phase service to the female 30-amp connector. And the 30/20 adapter will properly connect the hot, neutral and ground to the extension cord.
What’s wrong with this picture?
Well, the real problem is that now you’ve created a situation where it’s very easy to overload any 15- or 20-amp extension cord you plug into it with up to 50 amps of current. While I see (and don’t really like) 50-to-30 amp adapters used to power a 30-amp shore power RV from a 50-amp pedestal outlet, that’s not extremely dangerous since the 30-amp main circuit breaker should (in theory) protect the 30-amp cord from overload.
However, in your proposed hookup there’s no guarantee of a 15- or 20-amp circuit breaker on the end of your extension cord. In fact, I’ve seen a similar version of your proposed hookup used at campgrounds to power deep fryers and waffle makers on a picnic table. And yes, those extension cords were getting VERY hot. So never do this…
I found this really cool 50-amp to double 20-amp adapter cable last year which includes a pair of 20-amp circuit breakers, one for each 20-amp duplex outlet. This is heavy-duty construction with contractor-grade 20-amp duplex outlets (one on each side), plus resettable breakers (see the little red buttons). I think this adapter is the ideal solution for powering a 20-amp RV or appliance or extension cord from a 50-amp outlet. You can buy one HERE.
What about a 50/30-amp adapter with a circuit breaker?
Sadly, none exists as a commercial product. You would have to DIY one. However, while it is technically a code violation to use a 50/30-amp adapter without a built-in 30-amp breaker to protect the cord, there’s a bunch of manufacturers who make and sell them to the public, and I’ve never heard of one melting down.
Of course, your safety is dependent on your RV having an operational 30-amp main breaker, and nothing shorting out the short power cord on its way into your RV. So, while there’s a minimal danger from a 50/30-amp adapter, it does impose an additional wiring danger you all need to be aware of.
But any extension or shore power cord that accidentally carries more than its rated current will get very hot, and could melt down or catch on fire. Watch my video of this showing a 15-amp extension cord overloaded with 30-amps of current reaching nearly the boiling point of water in 5 minutes. So you need to be especially diligent if you’re using any cord without a properly sized upstream circuit breaker. Watch this video HERE.
Is there more?
Yes, read my full article explaining all about power adapters HERE
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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