Grounding the Service Entrance of a 480V grounded wye service

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bilbo336

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Article 250.24(C) states that "Where an ac system operating at less than 1000 volts is grounded at any point, the grounded conductor(s) shall be routed with the ungrounded conductors to each service disconnecting means and shall be connected to each disconnecting means grounded conductor(s) terminal or bus." The NEC Handbook says that if you have a grounded system the grounded conductor must be run from the service transformer neutral bus to the SE disconnecting means neutral bus and bonded to the grounding electrode, whether you use the neutral or not. We commonly design 3 wire 480V service entrances to switchgear or MCCs and do not use the neutral. If we need single phase voltages we install a transformer to handle the single phase loads. My question is can the "grounded conductor" from the transformer to the SE equipment be an uninsulated wire? So far, I have not found a requirement to use an insulated one and I have a contractor that installed an uninsulated equipment ground wire along with the three phase conductors.
 
I think Don made the call correctly. That's an exception I didn't know about. As you probably know, keep in mind that it needs to be at least as large as required by Table 250.66 even if you have no neutral load.
 
bilbo336 said:
Article 250.24(C) states that "Where an ac system operating at less than 1000 volts is grounded at any point, the grounded conductor(s) shall be routed with the ungrounded conductors to each service disconnecting means and shall be connected to each disconnecting means grounded conductor(s) terminal or bus." The NEC Handbook says that if you have a grounded system the grounded conductor must be run from the service transformer neutral bus to the SE disconnecting means neutral bus and bonded to the grounding electrode, whether you use the neutral or not. We commonly design 3 wire 480V service entrances to switchgear or MCCs and do not use the neutral. If we need single phase voltages we install a transformer to handle the single phase loads. My question is can the "grounded conductor" from the transformer to the SE equipment be an uninsulated wire? So far, I have not found a requirement to use an insulated one and I have a contractor that installed an uninsulated equipment ground wire along with the three phase conductors.
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I'm not commenting on your question. The answers you already have are good.

I am interested in why you think it is okay to not run the neutral to the first disconnect. The code seems pretty clear - doesn't matter if you use it or not.

Curiousity questions:
Just how big of a service are you discussing. Is this a 200A or a 2000A?

Most of the stuff I deal with, a 480V service will have engineerid drawings. Do you have drawings and an engineer of record?

ice
 
iceworm said:
I'm not commenting on your question. The answers you already have are good.

I am interested in why you think it is okay to not run the neutral to the first disconnect. The code seems pretty clear - doesn't matter if you use it or not.

Curiousity questions:
Just how big of a service are you discussing. Is this a 200A or a 2000A?

Most of the stuff I deal with, a 480V service will have engineerid drawings. Do you have drawings and an engineer of record?

ice
Click to expand...

I don't think the OP was suggesting that the neutral was not required the way I read it. I seemed clear that the OP knows that the neutral has to be brought to the service disconnect and sized per Table 250.66 even if there is no load on it.
 
texie said:
I don't think the OP was suggesting that the neutral was not required the way I read it. I seemed clear that the OP knows that the neutral has to be brought to the service disconnect and sized per Table 250.66 even if there is no load on it.
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Yes, the tone was such that i thought that as well. But ...

bilbo336 said:
... We commonly design 3 wire 480V service entrances to switchgear or MCCs and do not use the neutral. If we need single phase voltages we install a transformer to handle the single phase loads. My question is can the "grounded conductor" from the transformer to the SE equipment be an uninsulated wire? So far, I have not found a requirement to use an insulated one and I have a contractor that installed an uninsulated equipment ground wire along with the three phase conductors.
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So, I don't know.

ice
 
Thanks

Thanks

Thanks for the prompt replies. In answer to iceworm's question the situation is that the contractor installed the SE per the design docs. I caught the missing neutral when I was looking at the installation and was looking for a way out of having to remove the installed cable and repulled a new 4 conductor cable. This would have required an outage at an operating facility and the client wasn't very happy about that. The new service is an 800 amp service. Thanks to don_resqcapt19 for the exception and for making my life a bit easier.
 
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PS

PS: I have changed our design practice to always use a four conductor (3 phases and a neutral) cable for this type of service - 38 years in this business and I'm still learning. :)
 
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