Montana Owners Club - Keystone Montana 5th Wheel Forum - View Single Post - Does 50 amp hookup actually have 240 vac in the RV?

firetrucker · 06-27-2018, 03:41 PM

Everybody has their own image of what the electrical connections are for the RV, and, remarkably, most of them give the right result, or close to it. The trouble comes in trying to understand someone else's description. Let's try one more and hope it simplifies things.

Imagine the 30 amp park connection as an extension cord plugged into a 120 V 30 amp receptacle. Imagine the RV as two separate plug strips, each with a 50 amp circuit breaker. If I plug one strip into the extension cord, I'll power up anything plugged into it, until I reach a maximum of 30 amps (3600 W). Then the park circuit breaker trips.

If I plug the second strip into the extension cord, too, then I'll also power up anything plugged into that one, but still with a maximum of 30 amp draw until the park breaker trips. If I'm careful, I can get everything in the trailer to work, but maybe not at the same time.

The park's 50 amp connection is like having two extension cords, each on a separate 50 amp 120 V circuit. I can plug each of my plug strips into its own extension cord and draw up to 50 amps (6000 W) on each strip until the circuit breakers in the strips, or the circuit breakers in the park, trip.

Now if it were as simple as that, the park would have to supply an awful lot of current over those 120 V circuits and use very, very large gauge wire. So they use a 240 V circuit instead, which neatly splits into two 120 V circuits because of the power transformer, and their wiring only has to carry half as much current. You can mostly ignore this.

What you can't ignore is that in your 50 amp extension cord, the two neutral wires from the plug strips are combined into one. If that wire comes loose or breaks, you now have one 240 V circuit coming into the RV, not two separate 120 V circuits. That means that across everything plugged into those plug strips, you've got more or less than 120 V, and a lot of those things don't like that, especially motors and electronic circuits. The smoke escapes, and they stop working. Some things that have external power supplies that operate from 120 V to 240 V, like some computers and televisions, probably don't care, fortunately.

So, as someone has already said:

30 amp circuit, 30 amp total.
50 amp circuit, 100 amp total, but don't lose the neutral (get a cheap circuit checker).

And for the purist, you can talk about the power factor and how much current the neutral carries, but who cares?

06-27-2018, 03:41 PM	#39
firetrucker Montana Master Join Date: Oct 2004 Location: Gardnerville Posts: 749 M.O.C. #2165	Everybody has their own image of what the electrical connections are for the RV, and, remarkably, most of them give the right result, or close to it. The trouble comes in trying to understand someone else's description. Let's try one more and hope it simplifies things. Imagine the 30 amp park connection as an extension cord plugged into a 120 V 30 amp receptacle. Imagine the RV as two separate plug strips, each with a 50 amp circuit breaker. If I plug one strip into the extension cord, I'll power up anything plugged into it, until I reach a maximum of 30 amps (3600 W). Then the park circuit breaker trips. If I plug the second strip into the extension cord, too, then I'll also power up anything plugged into that one, but still with a maximum of 30 amp draw until the park breaker trips. If I'm careful, I can get everything in the trailer to work, but maybe not at the same time. The park's 50 amp connection is like having two extension cords, each on a separate 50 amp 120 V circuit. I can plug each of my plug strips into its own extension cord and draw up to 50 amps (6000 W) on each strip until the circuit breakers in the strips, or the circuit breakers in the park, trip. Now if it were as simple as that, the park would have to supply an awful lot of current over those 120 V circuits and use very, very large gauge wire. So they use a 240 V circuit instead, which neatly splits into two 120 V circuits because of the power transformer, and their wiring only has to carry half as much current. You can mostly ignore this. What you can't ignore is that in your 50 amp extension cord, the two neutral wires from the plug strips are combined into one. If that wire comes loose or breaks, you now have one 240 V circuit coming into the RV, not two separate 120 V circuits. That means that across everything plugged into those plug strips, you've got more or less than 120 V, and a lot of those things don't like that, especially motors and electronic circuits. The smoke escapes, and they stop working. Some things that have external power supplies that operate from 120 V to 240 V, like some computers and televisions, probably don't care, fortunately. So, as someone has already said: 30 amp circuit, 30 amp total. 50 amp circuit, 100 amp total, but don't lose the neutral (get a cheap circuit checker). And for the purist, you can talk about the power factor and how much current the neutral carries, but who cares?