Generator/ATS grounding/neutral issue

[beaucephas]

I have a situation I am trying to figure out. There is a building (3ph-4w-277/480V) with a standby generator and 3-pole ATS. The ground and neutral are not bonded at the generator. The frame of the generator is connected to a ground ring that surrounds the building and is connected to the building service. There is an equipment grounding conductor from the generator to the ATS, and one from the service to the ATS. There are four wires plus ground from the service to the ATS, but only three wires plus ground (neutral is run but not connected) from the generator to the ATS. Why would someone do this? It seems like it would create a fault. Obviously the remedy is to connect the neutral from the generator to the ATS, but I just want to make sure I am not missing something.

Is a generator considered separately derived if connected to the same ground ring as the electric service?

Thanks for your help.

 

[maghazadeh]

I have a situation I am trying to figure out. There is a building (3ph-4w-277/480V) with a standby generator and 3-pole ATS. The ground and neutral are not bonded at the generator. The frame of the generator is connected to a ground ring that surrounds the building and is connected to the building service. There is an equipment grounding conductor from the generator to the ATS, and one from the service to the ATS. There are four wires plus ground from the service to the ATS, but only three wires plus ground (neutral is run but not connected) from the generator to the ATS. Why would someone do this? It seems like it would create a fault. Obviously the remedy is to connect the neutral from the generator to the ATS, but I just want to make sure I am not missing something.

Is a generator considered separately derived if connected to the same ground ring as the electric service?

Thanks for your help.

What about feeder from ATS to the load side panel?
Is the panel 3ph, 3wire with no neutral? or is it 3ph, 4 wire?
IMO, neutral from Gen. to ATS must be connected.

Why would someone do this?

Because there are too many unskilled / unexperinced people in the field.

Is a generator considered separately derived if connected to the same ground ring as the electric service?

Yes, it is SDS.

 

[wirenut1980]

I agree with maghazadeh. The generator neutral needs to be connected to the normal source neutral at the ATS. The things that make the generator a SDS is the facts you have a 3 pole ATS, and the neutral and ground at the generator are bonded. See 250.30 for some guidance if you would like to research the Code. I see no problems connecting the grounding electrode conductors of the two sources to the same grounding electrode system.

 

[beaucephas]

The load side emergency panel is 3ph-4wire. That is why is it confusing to me.

What are some possible effects of not having the neutral connected at the ATS? Could this present a fault situation?

Just to make sure I am clear, does it have to be a SDS if connected to the ground ring? Currently the neutral and ground are not bonded at the generator. If it does have to be SDS, then the equipment grounding conductor from the generator to the ATS needs to be removed? Thank you again.

 

[maghazadeh]

The load side emergency panel is 3ph-4wire. That is why is it confusing to me.

What are some possible effects of not having the neutral connected at the ATS? Could this present a fault situation? If neutral isn't connected doesn't create fault. It just couldnot clear a fault.

Just to make sure I am clear, does it have to be a SDS if connected to the ground ring?
Has nothing to do with ground or ground ring. (generators, transformers, PV system all are SDS). Check for definition of SDS.

Currently the neutral and ground are not bonded at the generator. If it does have to be SDS, then the equipment grounding conductor from the generator to the ATS needs to be removed?
Do not remove any EGCs (equipment grounding conductors). The reason neutral and ground must not to be bonded together at the generator is because you have a 3 pole ATS. If you had a 4 pole ATS, then you must bond the neutral and ground together at the generator.

Thank you again.

Hope this helped.

 

[AZElectrical]

The OP says that the ground and neutral are not bonded at the generator, and the ATS is 3-pole, which means the neutral isn't switched. Unless I'm missing something, this is not a separately derived system.

I forgot a neutral between ATS and generator doesn't exist! When the neutral is installed, it won't be separately derived.