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We have a new 200 amp service, with a new meter box and service disconnect on the exterior of the house. Directly behind the meter box is a new larger 40 spot sub-panel.

We want to install a generator inlet because we live in an area that may lose power for many hours. We have gas appliances, including furnace, so a 30 amp inlet should be enough for a few hours running lights and refrigerators.

The main meter box and service disconnect cannot have an interlock attached the seimens manual. The sub-panel has a main breaker disconnect instead of a lug-load center, and that is where the interlock will be placed.

My question is regarding the ground and neutral coming from the generator inlet. The generator will have a floating neutral, BTW. Sub-panel the neural and ground are NOT bonded.

Can the neutral and ground from the inlet box be moved from the sub panel to the main disconnect bonded neutral/ground bar? The main feeder conductors are running through 1-1/2 inch rigid conduit from the main disconnect panel to the sub panel. It would probably be over 40% to add 4 more THHN 8awg wires through that raceway. I know 10 awg can work for 30amp, but I had a bunch of 8 awg sitting around.

The picture included is what I imaging the wiring looking like, the dashed line being the neutral.

enter image description here

BMC
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2 Answers2

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Neutral: nope. Must be taken from the same panel as the hots always no exceptions.

You have two disconnects - outside and inside. The answer to your question on grounds totally depends on how you have designated those two according to NEC 230.85.

You can't grab ground before the service equipment. So if the outside is service equipment and the inside is a subpanel you can grab ground outside.

Harper - Reinstate Monica
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I believe you will not be allowed to have the neutral and ground terminate in the bonded service disconnect, while the two 120's go to the subpanel.

NEC requires the neutral and power conductors to be in the same cable or conduit, so the electromagnetic fields caused by the current all cancel out.

Your proposed setup would have generator power in the disconnect/subpanel conduit, but not neutral. Any unbalanced 120V loads running on the generator would leave an averaged uncanceled magnetic field in the conduit, and another uncanceled magnetic field around the neutral in the disconnect box. NEC won't like that.

Alternatives: run another conduit between the disconnect box and the subpanel to put the 4 generator conductors in, or run a separate conduit from the inlet to the subpanel outside of the disconnect box for the 4 generator conductors.

Triplefault
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