residential feeder size

[Toros]

Hi,
An approved plan calls ,
#1 cu thhn wires feeding inside tenant sub panels of six unit apartm. Building. longest feed is 90 feed and largest demand is 70 amp and main tenant brker is 100A.

Should not be # 4 cu??

 

[electrofelon]

The wire does seem oversized quite a bit. It could be #4 if the system is 120/240 single phase, but would have to be #3 if a three phase system (I am guessing it is the former). Any derating for any reason?

 

[iwire]

Likely just a case of over doing it but that is not a bad thing.

 

[infinity]

At 90' and 70 amps IMO it's a waste of someone's money.

 

[buzzbar]

The wire does seem oversized quite a bit. It could be #4 if the system is 120/240 single phase, but would have to be #3 if a three phase system (I am guessing it is the former). Any derating for any reason?

What difference does it make whether it's a three phase or single phase system? Amps is amps, right? Please explain that.

 

[infinity]

What difference does it make whether it's a three phase or single phase system? Amps is amps, right? Please explain that.

I would guess that he's saying a 120/240 volt system would allow the use of Table 310.15(B)(7).