CONFUSED WITH NEUTRAL, GROUND, BOND

[maintenance man]

A underground feed in pvc 4 wire 480v is going out to another building to a mcc. From that mcc it is feeding a panel listed as 480/ 277 .
Is the fourth wire a neutral or egc ? When it leaves the mcc in gal pipe to a 480/277 panel there is no change over from a transformer 480-480/277 to get a neutral. The fourth wire goes to the neutral bar should it be bonded to the panel ? What is wrong here? I do not find any gec connection anywhere.

This is a older design I have not seen before just trying to understand how it was done then.
Thanks to all or anyone for their help with this design.

 

[George Stolz]

See 250.32(B)(1)'s exceptions. That should help.

 

[augie47]

It being an older design, as George pointed out, it could be a bit confusing.
If the MCC is the first disconnecting means, it should have a GEC regardless of the 4th wire being a EGC or a grounded conductor.
Is there any 277 volt load ?

 

[maintenance man]

Yes the lighting is 277v. does this panel get bonded ? Will there be a danger using the fourth wire as both neutral and a egc ?

 

[Smart $]

Yes the lighting is 277v. does this panel get bonded ? Will there be a danger using the fourth wire as both neutral and a egc ?

If it is "grandfathered", the neutral gets bonded to the building GES and the MCC ground.

Yes, there will be a potential danger, but a lot less than if not bonded.

 

[augie47]

Under the exception, the neutral can serve as the ground for the MCC. You need to bond it and establish a grounding electrode system. The run from MCC to your panel can use the conduit as EGC if it meets 250.118 and the conductor can serve as the neutral to an isolated bar.