Hello Mike,
If you have a 50-amp trailer and 30-amp service is the only service available at the campground post, can you show me a wiring schematic of the adapter pigtail I would use to adapt from 30-amp service to a 50-amp trailer. When we run across this situation I am always curious how this adapter can supply power to both 120-volt sides of our 50-amp trailer connections. Thank you for your comments on this subject. —Gary Reed
Hi Gary,
Here’s how it works. First of all, you need to understand that the 240-volt plug on your USA RV really doesn’t supply any 240-volt appliances (except in very rare circumstances). It’s really supplying two separate 120-volt services. If you take a look at the diagram below, you’ll see how a service panel in the USA is split down the middle to make 120 volts.
So to make a 30-amp to 50-amp adapter, you just need to go backwards. The TT-30 plug is wired to the 50-amp outlet with the Green ground to ground, and the White neutral to neutral. But the Black hot wire from the 30-amp plug jumps to both hot sides of the 50-amp outlet. Now, this doesn’t really generate any more power than a 30-amp outlet can provide; it’s just jumping the 120-volt power to both sides of the 50-amp outlet.
Let’s play safe out there….
Mike Sokol is an electrical and professional sound expert with 40 years in the industry. Visit NoShockZone.org for more electrical safety tips. His excellent book RV Electrical Safety is available at Amazon.com. For more info on Mike’s qualifications as an electrical expert, click here.
Mike, if you put a jumper between the red and black wire on a 50 amp service at the pedestal you will have a dead short. The BLACK wire and the RED wire are 180 degrees out of phase. Granted you can put both hot legs together but they MUST be the same phase i.e.. Black to Black or Red to Red, never Black to Red.
I tried to attach a diagram but this system won’t allow me to do that sorry.
Mike, if the two legs are different phases (they have to be to get 240V) wouldn’t you be creating a dead short by jumping between them? I always thought the 30 amp adapter just connected to one leg of the 50 amp plug.
I’d like to add a note. This will NOT give you 240 volts, although both sides of the service will have 120 volts. They are supplied by the same phase, so the voltage will not add.