Whats wire size is needed for a 125amp service feeders ?

MEP Electrical
4

NEC Table 310.15 (B)(16)

Using column for 75°C (167°F)

125 X .83 = 103.74

#2 CU

or

in ALUMINUM

#1/0

Up until 2011 for single phase service feeders you could have just used Table 310.15(B)(7) which is easier to understand. You will see that you get the same wire size sometimes. Table 310.15 (B)(16) considers more factors and is best.

3

#1 copper

2

115 A rated #2 CU conductors would be protected by 125 OCPD