Roger, just from the drawing alone:
It looks like the alternate feed is a resistance grounded wye, but the normal service is a solidly grounded wye. Is this the case and if so, is that kosher? Never seen that setup before, so I don't know.
Also, the number of poles on the transfer switch is not shown, is that specified elsewhere?
The normal supply transformer KVA is not shown.
That is the question I haveWhy are there four 5 kV cables on the normal supply service conductors, but three 5 KV on the generator service conductors?
I agree. The 350 THWN is fine for the grounded conductor for both the utility and generator sides.Seems only three would be needed for both.
Also the cables are not specified here whether copper or aluminum, single conductor or 3 conductor, so not sure on the ampacity.
I am guessing many of these questions are answered elsewhere. Other than that, looks ok to me!
Interesting question Roger but I'm afraid the real answer is probably the most boring one: someone messed up the number of conductors while making the drawings and it slipped through...
Skeshesh, you hit the nail on the head but the kicker is, they are trying to say it is correct.
I threw it out here wondering if someone may have come up with the same reasoning they are using to justify the design.
Roger
I threw it out here wondering if someone may have come up with the same reasoning they are using to justify the design.
Roger
One wild guess is that I have seen utilities require and EGC and neutral in the service. Maybe one of the 5 kv cables should have been noted as a 600 v cable.
When you find out please let us know. Also do you need to size the fused disconnect below the transfer sw? what does it feed?
So you mean to say they provided a reason? I'd like to hear it if you don't mind (I guess I could wait a few hours so the others can participate in the fun guessing game!)
Why 4#350 from the utility incoming xfmr. if the neutral ground bond is located in the main switchboard? (as noted already)
Are there any life safety loads? if so is the transfer device UL rated for the application of an automatic transfer switch? Does UL1008 or UL2200 apply?
If the system is resistance grounded is 600V insulation on the ground conductor adequate? (when the ground fault occurs dosen't the ground voltage become elevated??)
Is the incoming service "#C7" a customer or utility owned transformer.
Is 6"C required seems like 5" would be sufficent?
What about a conduit for generator controls (engine start signals, etc.)
Any overcurrent protection at the generator?
thats all I can think of for now...
Roger
I talked with a few other electrical engineers here at .......... and below are responses to the questions you brought up while I was on-site on Wednesday.
1 ? The neutral (or grounded) conductor run from Incoming Service #C8 to MSB-C8, and Incoming Service #C7 to MSB-C7, must be the medium voltage (5 KV) cable type, as shown on Sheet E605. The ground conductor (or in this case supplemental ground) shall also be run from Incoming Service #C7 to MSB-C7, and Incoming Service #C7 to MSB-C7 (as shown on Sheet E605); however, this ground conductor shall not be installed within the 6? Conduit with the four (4) medium voltage cables for each service. This supplemental ground conductor shall connect the grounding system at the utility XFMR with the grounding system at the main switchboard (for each medium voltage service).
Per you current installation, you have not run a medium voltage cable for the (neutral) grounded conductor and the THWN/THHN ground conductor is in the 6? conduit (with the three medium voltage phase cables). Please correct both of these items before energizingthe CEP.
Since the generator/standby system is an impedance grounded neutral system, the neutral is required to be fully insulated with the same insulation as the phase conductors: ref. 250.186(B). I understand a neutral conductor is not run from the generator. However, because the transfer switch is three-pole with solidly-connected neutral, the neutral (grounded) conductor from the service must be equivalently insulated because the code does not relinquish the requirement when the source neutral is not run to the system disconnecting means.Bob, in this case the utility does not require an EGC and in fact they have agreed with my stance that the grounded conductor only needs to be a bare conductor
This statement they sent you is a written equivalent of what the drawing shows. I think it's incorrent. If I send you an email writing 2+2 = 5, it wouldnt matter if I follow it with an official statement saying "Roger, please note that two plus two shall equal five" - it's still wrong.