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Old 06-17-2011, 06:33 PM   #1
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Modifying a Backup Generator Setup


I live in an old farmhouse in the country and one of the previous owners had the electrical system set up to be hooked up to a 220V generator if the power goes out. Off a 30A 220V breaker in the main panel the line goes down to a transfer switch (only switching the 2 hot legs, not the neutral) then through a 30 A "safety switch" and then into a 4-breaker subpanel. The subpanel powers my water pump, natural-gas boiler, fridge and the basement light. In a winter emergency I'd need heat and water, in the summer I'd like the fridge and water, so my total emergency power needs are under 20 A at 110 V.

If I have a 3000 W (4000W peak) generator that only has 110V out (a 30A twist-lock and 4 standard outlets) is there any reason I can't wire the transfer switch so that only one of the sub-panel legs gets power? And secondly, could I hook up both legs from the transfer switch to the hot from the generator so all 4 breakers would be energized? There is not, and never will be, any 220V breaker in this panel and when flipped the 2 hots are isolated from the main panel.

I've read that any sort of setup with this generator going into the house will require me to make sure the generator neutral is floating as it doesn't transfer at the switch. Is there anything else I need to be concerned with?

Thanks for your time.

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Old 06-17-2011, 07:07 PM   #2
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Modifying a Backup Generator Setup


The neutral from the transfer switch to the subpanel would have to carry the full generator load (not just the expected maximum you would be using). For example 8 gauge for a generator that has a 40 amp built in breaker.

Because the neutral and ground are bonded at the main panel, it is necessary to either switch the neutral using the transfer switch or not have neutral and ground bonded at the generator itself.

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