Generator Switchboard

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infinity

infinity

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Let's say that you have a large generator (SDS) that feeds a switchboard 30' away with 12 sets of 750 kcmil conductors. The SBJ is in the switchboard, would you have any EGC's in the raceways between the generator and the switchboard? I say no and the neutral in the generator must be bonded to the metal parts of the generator or would you have SSBJs in those raceways? Opinions?
 
Sounds to be that 250.30(A)(1) Exception 2 and (A)(2) Exception could apply.
 
augie47 said:
Sounds to be that 250.30(A)(1) Exception 2 and (A)(2) Exception could apply.
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Someone just asked me this question and I don't have access to my codebooks at the moment. In my mind the generator gets treated as a service when it comes to bonding and grounding?
 
In my opinion the circuit between a SDS and the first disconnect always requires a supply side bonding jumper, no matter where the SDS is located, unless you have one of the rare cases where there is a neutral to earth bond at both locations.
 
Here's a photo of the generator connection, there appears to be a full sized SSBJ in each parallel raceway. Also there is an SBJ and a GEC landed in the generator.

Generator Connection.jpg
 
infinity said:
Here's a photo of the generator connection, there appears to be a full sized SSBJ in each parallel raceway. Also there is an SBJ and a GEC landed in the generator.

View attachment 2565521
Click to expand...
No need for the supply side bonding jumper to be the same size as the phase conductors...you can size it from Table 250.102(C)(1) based on the size of the ungrounded conductors in each raceway.
 
don_resqcapt19 said:
No need for the supply side bonding jumper to be the same size as the phase conductors...you can size it from Table 250.102(C)(1) based on the size of the ungrounded conductors in each raceway.
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I agree just like you would on a transformer secondary but is a SSBJ in each raceway actually required? Here in the photo you can see that the generator neutral is bonded directly to the EGC bus. One the other end the neutral in the switchboard is also bonded. If this were a service the bonding in more than one location would be permitted. If this were set up as an SDS like a transformer then the bonding jumper would only be in one location.
 
Per my earlier post
250.30(A)(2)
Exception: A supply-side bonding jumper shall not be required between enclosures for installations made in compliance with 250.30(A)(1),
Exception No. 2.
250.30)A)(1)
Exception No. 2: If a building or structure is supplied by a feeder from an outdoor separately derived system, a system bonding jumper at both
the source and the first disconnecting means shall be permitted if doing so does not establish a parallel path for the grounded conductor. If a
grounded conductor is used in this manner, it shall not be smaller than the size specified for the system bonding jumper but shall not be required
to be larger than the ungrounded conductor(s). For the purposes of this exception, connection through the earth shall not be considered as
providing a parallel path.

Seems this applies unless you have a metallic raceway that would create a parallel path.
 
infinity said:
The generator switchboard feeds many transfer switches, I believe both 3-pole and 4-pole dDo any epending on the load.
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Do any have solid neutral connections ?
If so would that make any N-G bond a violation ?
 
This is not an outdoor generator it is located on the 4th floor inside of a building. Also in looking at the photo the SBJ appears to be much too small.
 
infinity said:
Someone just asked me this question and I don't have access to my codebooks at the moment. In my mind the generator gets treated as a service when it comes to bonding and grounding?
Click to expand...
Notice, you called it a service, but Don (correctly IMO) called it an SDS. As an SDS I am with don
 
infinity said:
This is not an outdoor generator it is located on the 4th floor inside of a building. Also in looking at the photo the SBJ appears to be much too small.
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So with an indoor generator (SDS), you can only have a system bonding jumper at a single location.

It will be sized based on the sum of area of the conductors on a single phase and Table 250.102(C)(1).

Since this is a generator it is very likely that there is a flexible connection at the generator, and if there is you will need a supply side bonding jumper in each raceway sized per Table 250.102(C)(1) and the size of the ungrounded conductor in the raceway.
 
Is the SBJ on the generator a factory strap that the installer is supposed to keep or remove based on the system design? Assuming there is no OCPD on the generator itself, you should have the option of putting the SBJ in either the generator or the switchboard. However you can't have in both per 250.30A1.

If your OCPD is in the switchboard then you need an SSBJ ran in between the generators and the switchboard -- this regardless of where the SBJ is at the switchboard or the generator. 250.30A2.

On the sizing of the SBJ, based on the crimps in the photo, those look like aluminum conductors with a copper SBJ. So it's not a simple 12.5% rule. You get to apply note 2 of table 250.122C. I would question though if this is a factory strap.

Having some 3 pole xfr switches and some 4 pole then considering it an SDS isn't something I have seen. Would have to think about that one a little longer.
 
don_resqcapt19 said:
So with an indoor generator (SDS), you can only have a system bonding jumper at a single location.

It will be sized based on the sum of area of the conductors on a single phase and Table 250.102(C)(1).

Since this is a generator it is very likely that there is a flexible connection at the generator, and if there is you will need a supply side bonding jumper in each raceway sized per Table 250.102(C)(1) and the size of the ungrounded conductor in the raceway.
Click to expand...
This is my thought as well. Since there's an SBJ in the generator the load side of the generator terminals get wired just like the secondary of a transformer with no SBJ in the generator switchboard. Each raceway would contain an SSBJ based on the size of the conductors in each parallel raceway.

Last part of the equation, if each raceway where it enters the generator switchboard requires a bonding jumper from the EMT to the EGC bus that can be sized two ways,

One: each raceway would have a bonding jumper sized according to the conductors in each raceway or,

Two: a single bond jumper can be used for all the raceways based on 12.5% of the total kcmils of the parallel conductors.
 
I agree (My earlier post noting the exceptions only applied to outdoor transformers)
 
infinity said:
Here's a photo of the generator connection, there appears to be a full sized SSBJ in each parallel raceway. Also there is an SBJ and a GEC landed in the generator.

View attachment 2565521
Click to expand...

Just out of curiosity, how big is this unit? I think the largest single unit I've ever worked on was a 900KW at The Roundhouse (police HQ) in Philly. This one looks bigger
 
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