Wire Size

mstrlucky74

Senior Member
Location
NJ
Have 120/208 3P 4W 100A being fed from 3P 40A breaker. One drawing asking for 4#6 & another drawing asking for 4#8’s. Conductors should be sized off 40A breakers, correct? So #8’s ok.
 

kwired

Electron manager
Location
NE Nebraska
As long as there are no adjustments needed that reduce #8 to less than 40 amps, yes #8 is minimum size needed here per NEC.
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Electrical Contractor
Long distance may merit #6 but as kwired stated the #8 is compliant. I would definitely ask the engineer and get this corrected on the drawings
 

kwired

Electron manager
Location
NE Nebraska
It might also be a future consideration; ie 40 A now with a possibility of bumping to 60A later without having to pull new conductors.
Why not install the 60 amp breaker now if that is the case? Especially if is three pole or a 277/480 volt breaker. Your double pole plug on breakers 60 amp and below are usually pretty inexpensive and there is a possibility you put in a 40 now, though I'd still normally put in the 60 now if that was the reason.
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
Have 120/208 3P 4W 100A being fed from 3P 40A breaker. One drawing asking for 4#6 & another drawing asking for 4#8’s. Conductors should be sized off 40A breakers, correct? So #8’s ok.
Either conductor size is code compliant I would use the #8 unless there is a voltage drop concern.
 
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