Single Phase Service Feeding Three Phase Panel

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Leo1

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Los Alamos, NM
Is it acceptable with the NEC to have a single phase, 120/240VAC, 400 AMP main residential disconnect switch (located on outside of house with CTs & meter adjacent) feed a 400 AMP three phase panel-board on the inside of the home? The 400 AMP main disconnect it feed with a parallel run of #3/0 CU to each phase A and B (yes, same for neutral). At the 400 AMP 3-phase panel-board phase A is feed by one #3/0 CU from phase A of the 400 AMP main disconnect. The other #3/0 CU in the phase A of the 400 AMP main disconnect feeds phase B of the 400 AMP 3-phase panel-board. And last the 2-#3/0 CUs from phase B the 400 AMP main disconnect feeds phase C of the 400 AMP 3-phase panel-board.

I do not know why someone would do this unless the 400 AMP 3-phase panel-board was left over from another job and the contractor offered the home owner a discount for the 3-phase panel-board versus buying a new single phase panel-board?
 
Leo1 said:
Is it acceptable with the NEC to have a single phase, 120/240VAC, 400 AMP main residential disconnect switch (located on outside of house with CTs & meter adjacent) feed a 400 AMP three phase panel-board on the inside of the home? The 400 AMP main disconnect it feed with a parallel run of #3/0 CU to each phase A and B (yes, same for neutral). At the 400 AMP 3-phase panel-board phase A is feed by one #3/0 CU from phase A of the 400 AMP main disconnect. The other #3/0 CU in the phase A of the 400 AMP main disconnect feeds phase B of the 400 AMP 3-phase panel-board. And last the 2-#3/0 CUs from phase B the 400 AMP main disconnect feeds phase C of the 400 AMP 3-phase panel-board.

I do not know why someone would do this unless the 400 AMP 3-phase panel-board was left over from another job and the contractor offered the home owner a discount for the 3-phase panel-board versus buying a new single phase panel-board?
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I don't have a code issue with using the three phase panelboard. I do see improperly protected feeder conductors on A phase of the main disconnect - you have two panel buses supplied by a 200 amp conductor yet either bus could draw 400 amps without tripping overcurrent protection.
 
Code wise one problem, albeit no biggie, wold be the mfg label not matching the type service.
That said, the manner in which it is connected would be a violation. If I read correctly, you leave the disconnect paralleling the 3/0s but when you get to the panel you don't terminate them on the same buss so they are no longer paralleled which means you have one 3/0 protected by a 400 amp fuse.

opps posted same time as kwired...but at least we agreed :)
 
augie47 said:
Code wise one problem, albeit no biggie, wold be the mfg label not matching the type service.
That said, the manner in which it is connected would be a violation. If I read correctly, you leave the disconnect paralleling the 3/0s but when you get to the panel you don't terminate them on the same buss so they are no longer paralleled which means you have one 3/0 protected by a 400 amp fuse.

opps posted same time as kwired...but at least we agreed :)
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That MFG label possible says it is good for a 48 VDC system as well though.

Does single/three phase really matter? Or is it just important we don't apply more then rated voltage as well as not have too high of available fault current?
 
Another problem might be that in one of the three possible ways to put in a 2 pole breaker you would get two of the same leg.
 
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