310.15 (b) (6) apply to a 6 unit buildings service

[mike1061]

I want to change the service to a 6 unit apartment building. In Chicago. The load calculation came to a 400 amp, 240 volt, 1 phase service. 6 dwellings and a public panel. I believe the 310.15 (B) (6) table applies to each of the apartments 100 amp feeders. Meaning #4 CU, in 1" pipe. The question is does that section and table apply to the service riser? Meaning the from the weather head to the main disconnect and from the main disconnect to the meter bank? My guess would be no, but I'm not sure. The table would allow 500 KCmil in 4" IMC, outside to the main disconnect and 4" EMT inside from the disconnect to the meter bank. If I can't use 310.15 (B) (6) then I have to use 310.16. That requires 600 KCmil, in 3 1/2 IMC and EMT.
Thanks
Mike

 

[kwired]

Read first few words of the section ... "For individual dwelling units"

I think that means the section only applies to the individual feed for an individual dwelling unit and not a feed supplying multiple units.

 

[augie47]

Read first few words of the section ... "For individual dwelling units"

I think that means the section only applies to the individual feed for an individual dwelling unit and not a feed supplying multiple units.

Thats the way I see it also.
Actually, you can only use the 600 kcmil AL IF your calculated load is 385 amps or less. I would think parallel 250s might be easier to install.

 

[mike1061]

Thanks for the replies. That is what I thought. Then I was thinking it said for individual dwelling units, two-family, and multifamily dwellings.

But I looked again, for this reply and I see it says "for individual dwelling units OF one-family, two-family and multifamily dwellings.
Thanks
Mike

 

[mike1061]

Thats the way I see it also.
Actually, you can only use the 600 kcmil AL IF your calculated load is 385 amps or less. I would think parallel 250s might be easier to install.

This I don't understand. I meant 600 KCmil CU, anyway, 600 KCmil AL is only rated at 340 amps, using the 75 degree column. Several years ago an inspector made me change 500 KCmil CU to 600 Kcmil CU because they have to be installed using the 75 degree column because all breakers/disconnects are only rated for 75 degrees.

What would the parallel copper conductors be?

Thanks
Mike

 

[augie47]

This I don't understand. I meant 600 KCmil CU, anyway, 600 KCmil AL is only rated at 340 amps, using the 75 degree column. Several years ago an inspector made me change 500 KCmil CU to 600 Kcmil CU because they have to be installed using the 75 degree column because all breakers/disconnects are only rated for 75 degrees.

What would the parallel copper conductors be?

Thanks
Mike

Actually, I accidentally looked at the wrong column so my post was incorrect, but to address your point.
One must take into account 110.14 (C)(1) and not terminate the conductor at a rating higher than 100.14(C)(1) allows. Since most terminations are 75?, 500 kcmil would have a final (after adjustments) ampacity of 380 amps.
If your calculated load is actually 400 amps, then you could not use a 380 amp conductor.

If you elected to parallel conductors, you could use 3/0 Cu in separate conduits. If you were only using one conduit you would have to use 4/0 since (2) 3/0s per phase paralleled in one conduit would only be good for 360 amps.

 

[cowboyjwc]

I would agree that you do not need 100 amps to each unit. I've seen many 60 amp feeds for apartments.

As for the other part, sorry I'm having a hard time focusing today so I didn't really pay much attention to it.

 

[mike1061]

Thanks again
Mike