Generator, A/C, and phase questions

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supermanotorious

supermanotorious

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Joined
Jun 29, 2015
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Phoenix, AZ
I have a super reliable although somewhat noisy HF generator and want to run the whole trailer from it. The A/C is too much load for the 20A breakers but I suspect would be ok if configured for 120V off the 25A circuit. A friend mentioned something about phase and that if I wanted to use the 3-prong 20A outlet for the rest of the trailer needs, the twist-lock plug has to be configured for the same phase to run to the A/C. Is that correct? Essentially, how do I segregate the A/C and give it dedicated power?
 

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The twist lock is a 4-prong outlet, not 3, and has both 120v and 240v available.  If the outlet is rated for 25A (I can't tell form the photo), then it's 25A @ 120v, but there are two 120v circuits there, 180 degrees out of phase with each other. The 4-prong, 240v connector has 2x 120v hot pins, with 120v between each hot and the neutral pin, and 240v between the two hots (that's the "phase" effect).

The ground terminal is the J shaped pin; the neutral is opposite; and the two hots are on either side in between ground and neutral.

If your RV has 50A shore power, you can wire a twist lock adapter for the shore cord and plug directly to that outlet (it is designed to handle the split phase power). If the RV is 30A, you can only use one of the two 120v sources available on that plug.
 
I think to segregate the AC from the rest of the house, the simple way is to create a sub panel and move the air conditioner breaker and wiring to it. Then add a separate input plug to feed that sub panel. This would create the need to use two cords and have another source of sufficient capacity any time you plug in even without the use of the generator and need the air to function.
 
If you're asking about the main breaker IN the RV, it's a 30 amp. I'm not sure if that's what you mean however.

Gary RV Roamer said:
If your RV has 50A shore power, you can wire a twist lock adapter for the shore cord and plug directly to that outlet (it is designed to handle the split phase power). If the RV is 30A, you can only use one of the two 120v sources available on that plug.
Click to expand...

On another note, I'm going to experiment running the trailer off the 25A twist-lock, I think if we didn't try to run the A/C with any heavy amp draw equipment such as a heating element, we should be ok. The A/C has a 20 amp breaker in the fuse panel so 25 amp at the source should be sufficient in theory.
 
Yes, I meant the RV main breaker and the compatible shore cord (three prong plug on the end if 30A).

When making the RV adapter for the twist lock plug, connect only one of the two hots on the genset receptacle to the adapter. That way you get 120v only. To make an adapter you need an 14-30R receptacle (for the RV plug to mate into) and a 4-prong male twist lock for the generator side. Looks to be an L14-30 male twist lock. Twist locks are oOften called a Hubbell connector, after the originator.  Use 10 gauge wire to connect the two.
 
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