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Author Wiring of generator transfere panel - feeder sizing question
Travis

2005-07-08, 6:25 pm

I have a 150A service for my main panel. I want to install an
auxilliary panel as a transfer switch next to the main panel.

I think I've done my calculations correctly in sizing the feeder cable
required by the NEC to power this sub panel (from the main panel). Can
anyone verify this?

Here are the specs:

I have a total living space of 722 sq feet that I am hooking up to the
panel (722 x 3 = 2166VA)

I am also hooking up a refrigerator circuit (1500VA / 20A circuit)

According to the calculations total load = Connected load + demand load

Connected load = 3666VA
Demand load = 3000 + 233.1 = 3233VA
Total load = 6899VA

If I divide by 240 this would size my feeder (and breaker) to be at
minimum 28.7A. So if I went with a 3 conductor 10AWG with a 30 amp
dual pole breaker I should be fine, correct?

What if I just connected all of these loads to one of the buses in the
auxilliary panel? I would essentially be driving all current through
one conductor of the 3C/10 cable - would I need to essentially DOUBLE
the current requirement of the cable to do this?

Reason I ask is because the generator I have is only single phase 120v
- I can't evenly distribute the breakers in the panel between the two
buses, due to the fact that my generator would only be driving 1 of the
buses, while the main could *possibly* feed both.

Any help / ideas / suggestions to this would be greatly appreciated!

Travis

2005-07-08, 6:25 pm

Hmm - I just thought of something. If the 30A cable is appropriate,
and I load balance the breakers across the 2 hots from the main feed -
is it permissble to use a JUMPER wire from one pole of the generator
feeder breaker to the other pole of that same feeder breaker?
Essentially I would be running the same 120 volts to each buss. I
don't have any 240v circuits in this box.

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