I have job coming up ( the wood working plant previously posted), that I am to set a 480 volt panel on. The building at one time had some sort of 480 volt panel. The panel has been removed, and all that is there now, is about a 20" X 20" junction box with 2 pair of feeders coming into the back of the box. The feeders seem to be paralled. There are 4 3/0's in each pvc run into this junction box. It is coming from an outside transformer.
I'm now pretty sure they had a 400 amp panel originally. I have a quesion now though while looking through the code. The 3/0's are good for 200 amps, and parralleled you have 400 amps. The service is 480/277 volts. The fourth wire in each conduit, I assume is the neutral. In this application, does the neutral not have to be counted when derating? Obviously it don't. I guess this comes with the code reference, of when the neutral is only used to carry the unbalanced current from other conductors, it don't have to be counted. Am I correct in this?? Another question, in what situation would the neutral be counted as a current carrying conductor?? Thanks again... I deleted most of the original message. It was not needed now. Thanks again, Steve

edited again. Forgot to say, that I will probably go back with a 400 amp. 30 circuit panel with main breaker, then the wires will probably be long enough to reach the lugs on the new panel ( bottom lugs ). With the machinery that may be added, the extra amperage and spaces might come in handy down the road, since it seems this project is not exactly planned out like I would like it by the owner.... Still on the drawing board .. Steve

[This message has been edited by sparkync (edited 03-03-2005).]

[This message has been edited by sparkync (edited 03-03-2005).]

[This message has been edited by sparkync (edited 03-03-2005).]

Just deleted some of my original question. I guess it was a little confusing. I just like to make sure that I'm correct in my decisions, since it may cost a lot, for the smallest mistake, if I don't figure right the first time. I don't like, and can't afford to keep doing something over and over again, especially when I'm talking thousands of dollars, 480 volt panels, breakers, etc Thanks again .. Steve

Sparky"
Yes, parallels will give you 400 amp. Now, depending on the load to be connected (quan. of 277 lighting, if ballastsed) will determine if the neutral is a current carrying conductor.

You neglected to state the insulation on the existing wiring & pipe sizes.

310.15 (4)(c) 2002 NEC is the article you need for the explanation.

Although not NEC required, & dependent on the conduit size, you may want to consider 4/0 THHN Cu., and a 'full' 42 circ panel.
(Not that much extra cost for the additional space) Remember the cb's are pricey also.

Hope this helps,

John