changing 480W-3PH-3W to 480V-3PH-4W panelboard

[DW98]

I need a neutral for 277/480V fan terminal units. Can a neutral be added and a neutral terminal strip be added to an existing 480v-3p-3w panelboard and the panelboard relabeled 277/480V-3PH-4W. Are these field modifications permitted? UL listing invalidated?

 

[ron]

Can't do it.

Install an isolation transformer 480-480/277V and a downstream 480/277V panelboard.

 

[electrofelon]

Can't do it.

Install an isolation transformer 480-480/277V and a downstream 480/277V panelboard.

Ron not sure I agree. Sounds like there is a 480/277 supply, just the panelboard is marked 3 wire. Now if the OP is talking about stealing a neutral from another system then i agree no.

 

[ron]

Ron not sure I agree. Sounds like there is a 480/277 supply, just the panelboard is marked 3 wire. Now if the OP is talking about stealing a neutral from another system then i agree no.

We don't know what we don't know.

He wrote about UL listings being invalidated. If there is a factory nameplate that specifically says 3phase 3 wire, then I don't think you can make it 4 wire, even if you find the correct system's grounded conductor.

 

[electrofelon]

An interesting question. Considering that a panelboard is mounted in a cabinet, it doesn't seem like the panelboard has any business caring about whether there is a neutral buss in the cabinet. Get into
The system grounding configuration, I could see it, but "3 wire" doesn't say anything about that.

 

[DW98]

the MSB is 277/480V. E.C. is going to check to see what wiring is actually pulled. may have to install a 480D to 277/480 xfmr and panelboard

 

[jap]

the MSB is 277/480V. E.C. is going to check to see what wiring is actually pulled. may have to install a 480D to 277/480 xfmr and panelboard

Are you saying you have an existing 480v 3 wire subpanel (Labeled as such) fed from a 480/277v MDP that you want to pull a neutral too, and change the cover to now say that the subpanel is 480/277v since you added a neutral to it?

If you have 480/277v available already I don't see why you'd have to install a transformer.

JAP>

 

[infinity]

For us the 3 wire panelboards and the 4 wire panelboards are exactly the same except the 4 wire has a neutral bar that bolts to the back of the cabinet.

 

[electrofelon]

If you have 480/277v available already I don't see why you'd have to install a transformer.

JAP>

I dont either, unless circumstances are that it is cheaper to buy and install a transformer to make a neutral instead of pull in/repull the feeder with a neutral.

 

[LarryFine]

Considering that using a transformer would also require a GEC too, i'd definitely consider both before going that route.