Three phase Disconnect, (2) single phase panels

[Npstewart]

I have a existing building with a three phase 400A disconnect outside feeding two single phase 200A MCB panels inside. Can anyone think of a reason why this would be installed this way? I would think this would create a extremely unbalanced load. Any opinions? This is in a residential area. Im thinking at one time they had a open delta service and then converted to single phase. I have a call into the POCO to confirm the voltage already.

 

[Dennis Alwon]

Is one phase abandoned, ie no voltage???

 

[jumper]

I may be wrong, but future expansion.

EX: 208/120Y 400 amp supply. 400 amp disco. Full sized neutrals.

2 single phase panels. One on A and B phase, one on B and C.

A= 200 amps, B = 400 amps, C = 200 amps

Add third panel later on C and A.

 

[Npstewart]

I will have to do another site visit to figure this one out. I just looked at the pictures again and now I see a 4" conduit off to the right (see photo). I think there must have been some type of service revision at some point. This is about 10 feet away from one pad mounted utility transformer.

 

[Npstewart]

Now that I look at that picture again, I see a small disconnect on the top left, I bet that is going to the 3rd phase. That is probably the only 3 phase circuit. I bet this is a delta service.

 

[sgunsel]

I have seen several three phase disconnects used on one-phase systems. Probably what was available or cheapest to install.