Working on a project at a remote location where power will be generated by onsite parallel units operating at 480V 3-phase. The power generators will be connected to a common switchboard bus then the switchboard main disconnect will be the feed out to the main distribution panel. My plan was to have the neutral to ground bond occur in the switchboard and the ground rods bond here at the switchboard. The power generators will not have a neutral-ground bond. No ground rods at the generators and separate ground and neutral wires will be ran between the switchboard and generators. I am looking for NEC references to back this up as I am having a hard time grasping not treating them like a utility as in having each power generator grounded with rods, a N-G bod at the alternators, and a single "grounded" conductor ran from each unit to the switchboard then having them main N-G bond. There is no GFI requirements. If the utility was involved and there was a transfer switch, then NEC 250.11 and 250.12 would make this clearer, but no utility.
onsite power generation and neutral ground bond
- Thread starter mjmike
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- Connecticut
- Occupation
- Engineer
You need to follow 250.30 with regards to grounding.
If there is an OCPD with each generator, then 250.30(A)(1) would require the bonding to be done at the generator.
If the first OCPD or disconnecting means is at the switchboard, then the bonding could be done there.
If there is an OCPD with each generator, then 250.30(A)(1) would require the bonding to be done at the generator.
If the first OCPD or disconnecting means is at the switchboard, then the bonding could be done there.
- Location
- Connecticut
- Occupation
- Engineer
I would think that the non-fused disconnect would be the "first system disconnecting means."
The system bonding jumper connection can be made anywhere between the source (the generator) and the disconnect, but not at the switchboard.
Is it better to have a N-G bond at each unit with ground rods at each unit, run 1 "grounded" wire from each unit back to the switchboard like the utility, then have the N-G bod there with the grounding electrode? If I have to bond at each disconnect, then I can have a common ground rod point and N-G bond like with a utility fed electrical system.
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- Location
- Connecticut
- Occupation
- Engineer
You can't "rebond" the N-G at the switchboard, that would violate 250.30(A).
You can use a common grounding electrode and a common grounding electrode conductor per 250.30(A)(6).
Ok, that makes sense. So I can have the N-G bod at each generator, put in the ground counterpoise, and then run a bonding jumper from the common counterpoise to each generator. Then keep the N&G separated from there out. I think my stumbling point is I am used to having the electrodes with the N-G bond at the service disconnect location.
I guess my alternative could be to remove the local disconnects since the switchboard is beside the generators. Then, the switchboard would be the first disconnect. I may need a lock-off devise for the breaker so it is capable of being locked in the off position if I remove the local disconnect.
I guess my alternative could be to remove the local disconnects since the switchboard is beside the generators. Then, the switchboard would be the first disconnect. I may need a lock-off devise for the breaker so it is capable of being locked in the off position if I remove the local disconnect.
separately derived?
separately derived?
the generators don't meet the definition of separately derived systems. I would have left the bond off at the gen sets and put the service in like a noral service.
separately derived?
the generators don't meet the definition of separately derived systems. I would have left the bond off at the gen sets and put the service in like a noral service.
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