3 pole transfer switch

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don_resqcapt19 said:
This is all on the plant side of the service. The system is 480y/277 solidly grounded, but with no line to neutral loads. The transformer is 2000 kVA and the gen set 2000kW. Eight sets of three 500's with 1/0 supply side bonding jumpers between the two sources and the ATS.

The transfer switch is rated at 3,000 amps. It is a GE/Zenith switch, but not sure of its construction. ...
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Okay. Did not know that from the first post. I still don't have any experience with large transfer switches - all I have seen are in switchboards. And I did not do the designs. Still the physics is the same.

So, I'm guessing: the conductors are installed, the gen NG bond is installed, the xfm NG bond is installed. And, it is no longer an option to pull in a neutral separate from what you are calling the supply side bonding jumper.

And the issue is to figure out if the installation meets code - as in this is an AHJ problem? Or are you trying to figure if the install is a good design - as in a customer spec issue? These are really two separate issues.

don_resqcapt19 said:
I am not aware of a requirement to run the grounded conductor to the first disconnect for an SDS. It is there for a service, but not there for an SDS.
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That's true, 250.24.C applies to services. However, the system still has an NG bond in two locations. Not a good idea. However, as you said, in this case, it shouldn't matter - hopefully true.

I won't be any further help in a code discussion. Previous posts have that well covered

However:
Looking at this from a design standpoint. You have two paralleled non-SDS feeders separated by 3pole CBs - probably with paralleling gear. And the neutrals are solidly connected through 8 - 1/0 CU.

If this is the case, a code discussion, while interesting, doesn't change these were not particularly good design choices. This is not a cookie cutter installation suitable for a code designed project.

Two that come to mind are:
  • GF protection. Where is that exactly? Even though there are no line-neutral loads, I can see that as being a problem.


  • And, of course, isolation for maintenance.

After it is decided the installation meets code, I'd be interested in how these two are handled.

ice
 
don_resqcapt19 said:
This is all on the plant side of the service. The system is 480y/277 solidly grounded, but with no line to neutral loads. The transformer is 2000 kVA and the gen set 2000kW. Eight sets of three 500's with 1/0 supply side bonding jumpers between the two sources and the ATS. ...
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Couple of curiousity questions - not part of the code discussion. As $S alluded:
Is there OPC between the gen and the switch? If not, I think you are short of copper - unless it is a 2500KVA gen

Is there OCP between the xfm and the switch?​

ice
 
The transfer switch is service rated and contains the OCPD (not sure of the rating). The OCPD in the transfer switch is the OCPD for the transformer.

I expect that the generator is 2000kW/2500kVA.

The transformer is existing as is the wiring between the transformer and an existing MCC. The generator and transfer switch are being added. There will be no AHJ other than the customer's engineer and he is ok with the current design.

My question was just based on code issues. As others have said with no neutral leaving either source, I don't any real world issues, just a possible multiple point of neutral bonding code issue.
 
don_resqcapt19 said:
... There will be no AHJ other than the customer's engineer and he is ok with the current design.
... My question was just based on code issues. As others have said with no neutral leaving either source, I don't any real world issues, just a possible multiple point of neutral bonding code issue.
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It's done, it is in. I wouldn't have done it that way, but the question is: Is it worth tearing it out? I wouldn't. But I would still look hard at any maintenance isolation issues or GF trip issues. Paralleled sources and no way to isolate the neutral for maintenance is a really bad design choice.

don_resqcapt19 said:
The transfer switch is service rated and contains the OCPD (not sure of the rating). The OCPD in the transfer switch is the OCPD for the transformer.

I expect that the generator is 2000kW/2500kVA. ...
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Assuming you are saying the first OCPD for the gen is the one in the transfer switch, then that is screwed up.

8-500s is good for 3040A. The 2500KVA gen FLA is 3007A. The conductors from the gen to the first OCPD is required to be 115%. And no, I would not consider that an empty code legal requirement.

The job being this far along, nobody is going to say, we screwed up we need to fix this. It will get rationalized. Heck maybe the gen is actually 2000kva.

ice
 
iceworm said:
...
Assuming you are saying the first OCPD for the gen is the one in the transfer switch, then that is screwed up.

8-500s is good for 3040A. The 2500KVA gen FLA is 3007A. The conductors from the gen to the first OCPD is required to be 115%. And no, I would not consider that an empty code legal requirement.

The job being this far along, nobody is going to say, we screwed up we need to fix this. It will get rationalized. Heck maybe the gen is actually 2000kva.

ice
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You asked about the OCPD for the transformer and that is the one in the transfer switch. I am not sure if the generator has an OCPD built in or not.
 
don_resqcapt19 said:
You asked about the OCPD for the transformer and that is the one in the transfer switch. I am not sure if the generator has an OCPD built in or not.
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I asked about the gen as well.
iceworm said:
Couple of curiousity questions - not part of the code discussion. As $S alluded:
Is there OPC between the gen and the switch? If not, I think you are short of copper - unless it is a 2500KVA gen

Is there OCP between the xfm and the switch?​

ice
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Although I did screw the question up a bit. It should have said "unless it is a 2000KVA gen" - as opposed to a 2000KW gen

ice
 
iceworm said:
I asked about the gen as well.

Although I did screw the question up a bit. It should have said "unless it is a 2000KVA gen" - as opposed to a 2000KW gen

ice
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I see that now...missed it before. If I get back to that job, I will check if there is an OCPD in the generator.
 
don_resqcapt19 said:
I don't any real world issues, just a possible multiple point of neutral bonding code issue.
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There may be one. See below.


Sahib said:
When a nearby POCO overhead phase line is grounded in such a way that the resulting high ground leakage current flowing and seeking better ground back to source through the unprotected neutral conductor in a building could damage its insulation.





But that would happen only if there were already a ground fault in the grounded wire inside the building.:cool:
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