I have a single inverter generator with a floating ground that connects to my house panel using a manual interlock and double breaker. It works well. I have a garage and shop on a separate meter and panel about 20 feet away. It is a separate feed from the power company transformer. Same transformer that feeds the house. Can I add an interlock and generator inlet box to the shop panel and feed both at the same time using a splitter cord on the generator? My main concern is that there are two separate grounds. Could I create a potential between those grounds? Any other hazards?
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I'm not certain whether there's a literal violation of electric code in this scheme but I do see a violation of principle.
The problem is this: you'll be tying the neutrals of the two services together. A two-pole circuit breaker interlock type transfer breaks only the line conductors, so regardless of whether the present interlock is selecting generator or grid power, the neutral is connected from transformer to panel to generator. If you now add a feeder from the generator to the shop building you'll create a ring of neutral. Current drawn by a load in the house will return to the house panel, where it will divide so that part returns to the transformer on the house service and part returns to the transformer via the generator and shop service. If one of the services is smaller than the other there could be a possibility of overloading the smaller neutral as well.
I believe if you used a 3- or 4-wire transfer switch at both locations rather than circuit breaker interlock everything would be okay.
Greg Hill
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