When paralleling multiple generators I have seen installations where the N/Grd. connection is located in the output section of the generator terminal cabinet, in others I have seen where the N/Grd. connection is made at the parallel switchgear and at the generator the neutral and grounds are isolated with the grounds connected to the generator frame and the neutrals connected to the “T0” terminal. Is there an advantage to one vs. the other? In reading IEEE 446 [Orange Book] it indicates that this connection is “usually connected to a common neutral bus within the parallel switchgear”. But does not comment on connections at the generator for parallel operations. Is there an industry preference or advantage one vs the other?
Grounding Parallell Gen's?
- Thread starter Mike01
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texie
Senior Member
- Location
- Fort Collins, Colorado
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- Electrician, Contractor, Inspector
Funny timing for this, we are having this discussion on a job now. In my case we have 3 750 KW machines in parallel. Set up as a SDS. Common bus inside the building, gensets outside. Each genset has main breaker on the machine.
Given these parameters, in our case it is my position that the system bonding jumper and GES connection must occur at each genset to comply with 250.30(A) and 250.30(C).
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- Placerville, CA, USA
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- Retired PV System Designer
Whether or not you need (or are allowed) a separate bonding jumper at each genset would seem to me to depend on whether or not there is a disconnect for the genset which interrupts the neutral. If there is, then you would, IMO, need a bond at each. And none at the main panel unless there is a neutral interrupting TS in between.
Is there grid power in the picture too, or are the three gensets all there is?
Is there grid power in the picture too, or are the three gensets all there is?
output breaker vs no output breaker
output breaker vs no output breaker
I would say that if the gen’s have an output breaker then yes the N/G bond would be at the gen breaker with any N/G links removed in the parallel switchgear. I have seen some recent installations where the generator manufacture / engineer have forgone the output breaker and connect to a main breaker in the parallel gear. In this instance I would assume the N/G bond be at the parallel switchgear but I have also witnessed local installation similar where there is no gen. breaker and the N/G bonding at each gen. output. Trying to determine if there is any direct advantage to having it on one location vs another….
output breaker vs no output breaker
I would say that if the gen’s have an output breaker then yes the N/G bond would be at the gen breaker with any N/G links removed in the parallel switchgear. I have seen some recent installations where the generator manufacture / engineer have forgone the output breaker and connect to a main breaker in the parallel gear. In this instance I would assume the N/G bond be at the parallel switchgear but I have also witnessed local installation similar where there is no gen. breaker and the N/G bonding at each gen. output. Trying to determine if there is any direct advantage to having it on one location vs another….
texie
Senior Member
- Location
- Fort Collins, Colorado
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- Electrician, Contractor, Inspector
We are having discussion with the manufacturer's engineers and the engineer of record on this. Not sure that they agree on the correct approach yet. I'll let you know what we learn.
I think it is interesting that the code has so little specifics on this and it is not as cut and dried as it would seem. For example, similar things such as dual-fed services and transformers in parallel the code give a little more direction on grounding and bonding. As common as gensets in parallel are becoming maybe it is time for some more NEC details on this.
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