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

[wwhitney]

the ATS is 3-pole.

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.

also the b-phase from the generator runs through a main breaker before I can ground it.

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.

 

[don_resqcapt19]

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.

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.

 

[kreed]

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

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.

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?

 

[wwhitney]

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?

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

 

[kreed]

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

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

 

[don_resqcapt19]

My question now is, can I use the same ground rod(s) for b-phase and the GES

The GEC must connect to b-phase.

 

[wwhitney]

My question now is, can I use the same ground rod(s) for b-phase and the GES

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