Correct grounding for a standby generator on 240v grounded b phase

kreed said:
the ATS is 3-pole.
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So if you prefer to install the generator as an SDS, you can do that. If you prefer not to, then just use 2 of the 3 poles and solidly connect the B phase.

kreed said:
also the b-phase from the generator runs through a main breaker before I can ground it.
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It's permitted to have the grounded conductor disconnected by a breaker as long as it disconnects all the ungrounded conductors as well. As to where the GEC should connect with respect to this main breaker if you choose to install it as an SDS, I'd have to study 250.30 to say.
 
kreed said:
the ATS is 3-pole. also the b-phase from the generator runs through a main breaker before I can ground it. In my mind this would cause a ground fault. But I feel like I missing something too as the ground is just being used as a reference at this point.
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You can only have a ground fault when there are two connections to ground. Grounding B phase only results in a single connection to ground. To get a ground fault, you need an actual fault on A or B phase.
 
wwhitney said:
Yes, absolutely. You need an unbonded generator, so one with 5 connections: 3 corners, the center tap, and the frame, with no continuity between the frame and any of the other 4. Then you will only use 4 of those connections, the 3 corners and the frame, and leave the center tap unconnected.

Then if your ATS is 2 pole, you don't have to do any grounding at the generator, it's not an SDS and the solidly connected B/grounded conductor will be grounded at the service.

If your ATS is 3 pole, you do have an SDS and have to ground it accordingly, at the generator or at the first means of disconnect (if that is separate). Of course, you could choose to use only 2 of the 3 poles and connect it like a non-SDS.

Cheers, Wayne
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don_resqcapt19 said:
You can only have a ground fault when there are two connections to ground. Grounding B phase only results in a single connection to ground. To get a ground fault, you need an actual fault on A or B phase.
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ok, that's what I thought, hence a required grounded conductor for ground fault purposes. So, the way I have this installed, I will have a SDS. I know this already. Now, specifically how to establish my second connection to ground and for the service. I will ground b-phase directly to a ground rod. Can I also use this same ground rod as my grounding electrode for the purpose of connecting my GEC? Or do I have to drive a separate ground rod for that purpose?
 
kreed said:
I will ground b-phase directly to a ground rod. Can I also use this same ground rod as my grounding electrode for the purpose of connecting my GEC? Or do I have to drive a separate ground rod for that purpose?
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If the generator is in or alongside the building, then the building should have a single GES with all the grounding electrodes interconnected, and both the service GEC and the generator GEC should connect to that GES.

If the generator is remote from the building, it gets its own GES.

GES = Grounding Electrode System, e.g. 2 rods plus whatever other grounding electrodes happen to be present. [And if you have a Ufer or other non-water pipe electrode, you don't need the 2 rods.]

Cheers, Wayne
 
wwhitney said:
If the generator is in or alongside the building, then the building should have a single GES with all the grounding electrodes interconnected, and both the service GEC and the generator GEC should connect to that GES.

If the generator is remote from the building, it gets its own GES.

GES = Grounding Electrode System, e.g. 2 rods plus whatever other grounding electrodes happen to be present. [And if you have a Ufer or other non-water pipe electrode, you don't need the 2 rods.]

Cheers, Wayne
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Yes that part I understand. All conductors from the generator will be electrically isolated/independent of the utility. So I definitely have a SDS with the generator. My question now is, can I use the same ground rod(s) for b-phase and the GES
 
kreed said:
My question now is, can I use the same ground rod(s) for b-phase and the GES
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If you mean for the service and for the generator, then the answer is yes you may, and if they are at the same building, you must. All the grounding electrodes at the building get interconnected. Then one GEC goes to the service, another GEC goes to the generator.

Cheers, Wayne
 
wwhitney said:
Is that your interpretation of 250.26, or do you have another reference in mind?
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When combined with 250.20(C)(1) and the definition of Neutral Point, it's required to ground the neutral if (but only if) the neutral is used as a circuit conductor. Therefore it would be prohibited to corner ground instead if the neutral is used as a circuit conductor.
 
jaggedben said:
When combined with 250.20(C)(1)
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Not finding a 250.20(C)(1) in the 2023 NEC, did you mean 250.20(B)(1)? Not seeing how 250.20(B)(1) is relevant, as it's not possible to ground a 3 phase 240V delta with one coil center tapped (no wye point) so that all the ungrounded conductors are less than 150V to ground.

But upon reflection I agree that "use" in 250.26(5) means "as a circuit conductor" and so if for each of the 3 points on the center-tapped coil you have some load connected, you must ground the neutral. That would seem to create a possible dilemma for the OP if the generator has any internal 120V loads connected to the neutral.

Cheers, Wayne
 
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