sub feeder size

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almcvay

Member
I have been told that we that the code has changed for sub feed panels in aparments. can someone help ?
what is the new size wire for 125 amp service ?
also where can i find this in the code book?
the apartments I am bidding are N.C.

Thanks Al
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
Your question is not simple because there is much you have not told us. T. 310.16 has not changed but se cable 338.10 in particular is now limited to 60C under certain conditions.
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
He may be referring to Table 310.15(B)(6)


It could be he is referring to art. 310.15(B)(6). If these sub panels are multifamily dwellings that carry the entire load of the service using the wires or cables mentioned then T. 30.15(B)(6) could be used.

To me that wasn't a change but a clarification, of course, this clarification is a change. :smile:
 

celtic

Senior Member
Location
NJ
I just want to know what size wire to use for 125 amp panel.
I dont have a set of plans.


:-?

Tap rules, voltage drop....?

You know more about the job w/o plans than we ever possible could.

Give us some more to work with!
 

almcvay

Member
24 unit apt. 12 on each end of build. 125 amp breaker for each apt. with less than 100 ft. run to apt. each apt. has a 125 amp main breaker panel with a 125 amp main at the gangable meter center.
what i need to know is what size wire to run from the meter to the apt. panel
someone said that the code has changed and i need to use 2/0 alum. ser

thanks Al
 

curt swartz

Electrical Contractor - San Jose, CA
Location
San Jose, CA
Occupation
Electrical Contractor
What is the service voltage? I'm guessing 208/120 with 24 apartments. If that is the case 2/0 AL would be correct if the calculated load is less than 115 amps. If the calculated load is between 115 and 125 you would need 3/0 AL. If the service voltage is 120/240 you could use 1/0 AL per Table 310.15(B)(6)
 

almcvay

Member
It is 120/240 volt.
why is it not the same on 3 phase 120/208?
the main is 125 amp single phase for each apt. why would it be 2/0 on 120/208 and 1/0 alu on 120/240?
 

acrwc10

Master Code Professional
Location
CA
Occupation
Building inspector
It is 120/240 volt.
why is it not the same on 3 phase 120/208?
the main is 125 amp single phase for each apt. why would it be 2/0 on 120/208 and 1/0 alu on 120/240?

Because 310.15 (B)(6) gives you some wiggle room on service/feeders on 120/240 but not 120/208.

Table 310.15(B)(6) Conductor Types and Sizes for 120/240-Volt, 3-Wire, Single-Phase Dwelling
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
If the service voltage is 120/240 you could use 1/0 AL per Table 310.15(B)(6)

Only if the feeder to the unit carries the entire load of the apt. If, for instance, there is a disco at the service where the a/c is fed, then the ser cable cannot use T. 310.15(B)(6) but must use T.310.16. In that case you could possibly use 2/0 aluminum if the calculated load is not greater than 115 amps. Otherwise you would need 3/0 aluminum.
 
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