bonding

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rmonroe

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I have two different issues?Recently we were doing same work on a 480VAC 800AMP 3-wire bus line system (No neutral supplied to this busway). We had to shut down this busway in order to perform the task that we needed to do. As soon as I open the switch to the bus part of the plant lighting was shut off. The plant lighting is all 277VAC, which after tracing the feeder to the lighting panel down it was supplied by this 800AMP bus. What does that tell you and where do I find this in the NEC?

In the same plant we were running some standard 120VAC 20AMP circuits. A single-phase 240/120VAC 40KVA transformer supplied the panel, which is supplied by the same 800AMP busway. When I removed the panel cover I notice that the neutral was not bonded to the building ground. Should I look inside the supply transform to see if the neutral is bonded to ground at that point and if so would that be expectable?

Thanks
 
Re: bonding

The code requires a grounded conductor to be brought to each service disconnect per 250.24(B). After that, it only needs to be installed at a panelboard or in a circuit if it is going to be used.

250.30(A)(1) requires a neutral-to-case bond to made at the source of a separately derived system or at the first system disconnecting means. Since you have already determined the bond is not made at the first disconnecting means, the bonding should be at the transformer.
 
Re: bonding

If the lighting is 277 Volts, and there is no neutral, they have probably tied one side to the 480V bus, and the other side to a ground. This would be a code and a safety violation.

Edit: I guess I am assuming this is a 480V/277V wye system. The mystery to me is where they are getting 277V from with no neutral.

Did you say the second part right? A 240/120V transformer on 480V line? Assuming you meant it was a 480V to 120V transfromer, I would look for the bonding in the transformer and make sure it is there.

Steve

[ October 19, 2004, 09:26 AM: Message edited by: steve66 ]
 
Re: bonding

Last week I inspected a bldg. with a similar situation (where's the neutral?)...fortunately it was a new installation and I could ask the electrician....he picked up his neutral on the nearest cold water pipe!
 
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