Grounding 3 Phase 277/480 Disconnect with no neutral

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emueller15

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-The service is 100A 277/480V, which is not grounded
-Inside the building is a 80A fused disconnect with no ground or neutral

From the inside, 80A disconnect I am installing a control cabinet. How should I properly ground the control cabinet that is feeding several 480V motors?
 
electrofelon said:
This system is required to be grounded and have the neutral brought to the service equipment - unless you retract the 277 part. Is the utility supplying a neutral?
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I am having second thoughts about my answer. The code book is at the job so I cant check the wording, but I think it is something along the lines of if the neutral is not used and/or not brought to the service equipment then the system is not required to be grounded. Someone will chime in.....

Why not just bring in the neutral and ground it?
 
emueller15 said:
-The service is 100A 277/480V, which is not grounded
-Inside the building is a 80A fused disconnect with no ground or neutral

From the inside, 80A disconnect I am installing a control cabinet. How should I properly ground the control cabinet that is feeding several 480V motors?
Click to expand...

Per 250.24(E), an ungrounded service would still require a grounding electrode and grounding electrode conductor.

An equipment grounding conductor per 250.120 would be required with the feeder to the control panel.
 
emueller15 said:
-The service is 100A 277/480V, which is not grounded
-Inside the building is a 80A fused disconnect with no ground or neutral

From the inside, 80A disconnect I am installing a control cabinet. How should I properly ground the control cabinet that is feeding several 480V motors?
Click to expand...

How is the 277V derived without a neutral?
 
emueller15 said:
-The service is 100A 277/480V, which is not grounded
-Inside the building is a 80A fused disconnect with no ground or neutral

From the inside, 80A disconnect I am installing a control cabinet. How should I properly ground the control cabinet that is feeding several 480V motors?
Click to expand...

Just to confirm terminology, I think you mean you have a 480/277 Y service. If that is the case, then the neutral from the PoCo must be brought to the service and bonded, even if you have no line to neutral loads. After the service disconnect you would have only an EGC and no neutral available or required for line to line loads.
It's possible that you have some other service arrangement such as 480 delta, either ungrounded or corner grounded that would be entirely different. Also if it is an ungrounded service that means not grounded AT ANY POINT, including all the way back to the PoCo transformer(s).
 
IF it is ungrounded It would be a 480 delta, no 277 available, IIRC ground detectors would be needed.
The local POCO won't do them here anymore.
 
electrofelon said:
Not to be nit picky but it could still be a wye secondary transformer bank and even have the neutral point run to the customer but not be grounded and this would be ok by the NEC......
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If the power company did not bond XO at their end which they would when providing a wye service.
 
Service Grounding

Service Grounding

emueller15 said:
-The service is 100A 277/480V, which is not grounded
-Inside the building is a 80A fused disconnect with no ground or neutral

From the inside, 80A disconnect I am installing a control cabinet. How should I properly ground the control cabinet that is feeding several 480V motors?
Click to expand...

Ground and bond the neutral at the service disconnect and the metallic conduit will be your ground for the control cabinet unless specifications are calling for a separate ground
wire to be installed. I would like to know what this building is with a 100amp service and 80 amps going to a control cabinet. Is this a well building, are the lights in the building
277V, are there no 120V receptacles????????????????
 
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