Transformer Question?

[bdaddycr1]

I am refeeding two main 120/208 four wire services with a new 277/480 main then then placing a transformer at each of the two panels my question is , is since both of the panels were main panels, Do I have to isolate the neutral bar in the two panels then bond the neutral in the transformer and if not do I still bond the neutral in the transformer. I am feeding the transformer with 480 3 wire and the secondary is 120/208 4 wire
thanks wade

 

[roger]

Re: Transformer Question?

Wade for simplicity do this.

Install the GEC (to building steel or whatever) and EGC bonding to the XO tap at the transformers.

Now seperate the neutral and EGC at the panels.

The EGC could be the metalic conduit with proper bond bushings if needed,a wire conductor, or both.

If you use a nonmetalic raceway or cable from the transformer to panel you can forget the EGC and install a bonding jumper in the panel from the neutral bar to the can, this would be in addition to what we have already done in the transformer.

Roger

[ November 09, 2003, 08:52 PM: Message edited by: roger ]

 

[donnie]

Re: Transformer Question?

If you bond your Neutral at the transformer or if you attach you GEC to the transformer, then your two main panels would have to have Neu's and Grounds separated and have no grounding electrode attached to the panels.
Your Bonding Jumper and Grounding Electrode Conductor must be attached at the same point.

 

[roger]

Re: Transformer Question?

Donnie, if there is a nonconductive raceway or cable from the transformer to the panel, the neutral can be both Grounded and Grounding conductor and the panel enclosure will have to be bonded to this conductor. You would only have four wires from transformer to Panel.

See 250.30(A)(1) exception No. 1

Roger

[ November 18, 2003, 04:41 PM: Message edited by: roger ]