Twin 30 to one 50 amp RV cord

[GoldDigger]

Agreed. So, just to clarify, it is necessary to use a conventional Break-before-Make toggle switch.

Right, or two interlocked breakers, or anything else that results in a valid transfer switch operation.

You could do it with an appropriate form C contactor too, but two contactors without a positive interlock would not be OK.

 

[JFletcher]

If all the loads in the RV run on 120v, you can hook up two unsynchronized 120v, 30a generators.

Each generator hot leg will feed one hot leg in the panel; they won't be connected to, or interfere with, each other.

If they happen to be synchronized and in phase with each other, the white wire will carry the return current from both hot legs, but that will be a maximum of 60 amps on a wire with 50 amps ampacity. Not quite kosher, but not a catastrophe.

If they happen to be synchronized and 180° out of phase with each other, the white wire will carry the difference of return currents, same as in a residential 120/240-volt single-phase split-phase Edison circuit.

If they're unsynchronized, chances are they will also be running at slightly different frequencies and they'll drift from nearly-synchronized to nearly-anti-synchronized and back. The average current in the white wire will be equal to the current in either hot leg.

If there are any 240-volt loads, they aren't going to work. The voltage will drift from 0 (when they're synchronized) to 208v (when they're 120° out of phase) to 240v. (when they're 180° out of phase)

+1. Excellent explanation.

 

[OldSparks]

If all the loads in the RV run on 120v, you can hook up two unsynchronized 120v, 30a generators.

Each generator hot leg will feed one hot leg in the panel; they won't be connected to, or interfere with, each other.

If they happen to be synchronized and in phase with each other, the white wire will carry the return current from both hot legs, but that will be a maximum of 60 amps on a wire with 50 amps ampacity. Not quite kosher, but not a catastrophe.

If they happen to be synchronized and 180° out of phase with each other, the white wire will carry the difference of return currents, same as in a residential 120/240-volt single-phase split-phase Edison circuit.

If they're unsynchronized, chances are they will also be running at slightly different frequencies and they'll drift from nearly-synchronized to nearly-anti-synchronized and back. The average current in the white wire will be equal to the current in either hot leg.

If there are any 240-volt loads, they aren't going to work. The voltage will drift from 0 (when they're synchronized) to 208v (when they're 120° out of phase) to 240v. (when they're 180° out of phase)

I've yet to see an RV with two busses in the breaker panel. Maybe they exist. That configuration is, of course, common in residential panels. The RV's typically have a three-wire connection - Hot, Neutral, and Ground. All the loads are on one "leg".

 

[kwired]

I've yet to see an RV with two busses in the breaker panel. Maybe they exist. That configuration is, of course, common in residential panels. The RV's typically have a three-wire connection - Hot, Neutral, and Ground. All the loads are on one "leg".

Now enter the 50 amp supply cord that utilizes a NEMA 14-50 125/250 volt plug/receptacle. They certainly don't tie both ungrounded conductors to same bus, or else users will get a big surprise if they plug the cord in with all switches closed.

 

[GoldDigger]

I've yet to see an RV with two busses in the breaker panel. Maybe they exist. That configuration is, of course, common in residential panels. The RV's typically have a three-wire connection - Hot, Neutral, and Ground. All the loads are on one "leg".

You have not seen an RV with large enough loads (e.g. A/C) to require 240V.

 

[OldSparks]

Now enter the 50 amp supply cord that utilizes a NEMA 14-50 125/250 volt plug/receptacle. They certainly don't tie both ungrounded conductors to same bus, or else users will get a big surprise if they plug the cord in with all switches closed.

Thanks. I stand corrected.