Please explain the proper way of grounding and bonding a system consisting of a 480V Delta utility service and a 480/277V Wye connected generator. The service (phase) conductors from the utility company will terminate at a service entrance panel rated at 400A where the system ground will be established, i.e. water line, building steel, ground rod, etc. The phase conductors and equipment ground will extend to a 3-pole ATS. On the generator side of the ATS, I'm interested in knowing if I should run the neutral and equipment ground from the generator and connect them together at the ATS or tie the neutral and ground together at the generator and simply bring the phase conductors and equipment ground to the ATS. In the latter scenario, if I sized the equipment ground conductor from the generator to the ATS as a main bonding jumper would that suffice to carry the fault current? Like a transformer, I realize the neutral and ground must be connected together at the source of a separately derived system or first disconnecting means. Would that be the generator, ATS, or emergency panelboard? My intent is for the building system ground to be shared with the generator ground and thus the generator would not be a separately derived system. I realize that a low impedance fault current path back to the generator must be present to trip the overcurrent device in the event that a phase to ground fault occurs when the generator is in operation. Yes, I know, a lot of questions with few answers.
480V Delta Utility with 480/277V Wye Generator
- Thread starter jrturner
- Start date
- Status
- Location
- Windsor, CO NEC: 2017
- Occupation
- Service Manager
Re: 480V Delta Utility with 480/277V Wye Generator
I think your best option is to separate the grounding and neutral conductors at your generator, and run all conductors to all points, leaving the generator neutrals connected to the utility neutrals at the ATS.
It would be good for you to do a search on this topic.
No.
Not if you do not switch the neutral. You would need a four-pole TS for this option.
Without the neutral in the conduit running to the ATS, I believe you might have a violation of 300.3(B).
I think your best option is to separate the grounding and neutral conductors at your generator, and run all conductors to all points, leaving the generator neutrals connected to the utility neutrals at the ATS.
It would be good for you to do a search on this topic.
Re: 480V Delta Utility with 480/277V Wye Generator
Your installation of a generator supplying a grounded system to a building with a ungrounded system is unusual. Even though the ATS is a three pole, the generator is a separately derived system and must be grounded using 250.30. The system bond must be done at the disconnect for the generator, a GEC must be run to the generator disconnect, and the grounded conductor does not need to extend past the generator disconnect as there is a no need for it in the distribution system. Draw a one line diagram of your fault current return path for each system and then install it.
Fred
Your installation of a generator supplying a grounded system to a building with a ungrounded system is unusual. Even though the ATS is a three pole, the generator is a separately derived system and must be grounded using 250.30. The system bond must be done at the disconnect for the generator, a GEC must be run to the generator disconnect, and the grounded conductor does not need to extend past the generator disconnect as there is a no need for it in the distribution system. Draw a one line diagram of your fault current return path for each system and then install it.
Fred
Re: 480V Delta Utility with 480/277V Wye Generator
My last reply was based on the assumption that the delta into the building is ungrounded, you did not clarify if it was a grounded or ungrounded system, so if a grounded system, George gave you a good reply, if ungrounded system, then follow my first post.
Fred
My last reply was based on the assumption that the delta into the building is ungrounded, you did not clarify if it was a grounded or ungrounded system, so if a grounded system, George gave you a good reply, if ungrounded system, then follow my first post.
Fred
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