Wire size?

olly

Senior Member
Location
Berthoud, Colorado
Occupation
Journeyman Lineman / Distribution design and EC in my spare time
I am hoping someone could help as I dont have my code book with me. I need to know what size wire AL or CU is needed for a 125A service to a barn. And since it will be in conduit not URD so would THHN AL be okay or is it a better practice to go with copper conductors? The service length is 140'
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
For underground you would need THWN or XHHW. Are you concerned about voltage drop? If not #1 Cu (130 amps) or #2/0 (135 amps) would do.
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Electrical Contractor
Infinity is correcet however you could use 1/0 al instead of 2/0 alu,inum if the calculated load is not over 120 amps. Art. 240.4(B) allows us to use the next size breaker which is 125 amps even though the wire is only good for 120amps.

Given 140 feet you may want to size to the 2/0 al
 

olly

Senior Member
Location
Berthoud, Colorado
Occupation
Journeyman Lineman / Distribution design and EC in my spare time
Infinity is correcet however you could use 1/0 al instead of 2/0 alu,inum if the calculated load is not over 120 amps. Art. 240.4(B) allows us to use the next size breaker which is 125 amps even though the wire is only good for 120amps.

Given 140 feet you may want to size to the 2/0 al
If I go with 2/0 AL can I do a #1 AL neutral and than would I need a # 6 or a # 8 EGC?
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
The neutral needs to be large enough to carry the unbalanced load which #1 should work. For the EGC take a look at table 250.122
 
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