Code reference · NEC Table 310.16; 110.14(C); 210.20(A); 210.19(A) IN
What size wire for a 150 amp breaker?
For a 150 A breaker, the minimum copper conductor is 1/0 AWG (150 A at the 75°C column of Table 310.16, which is what standard breaker terminations allow per 110.14(C)). In aluminum, the minimum is 3/0 AWG (155 A at 75°C).
That answer assumes ≤3 current-carrying conductors, 30°C ambient, and a load that isn't continuous. A continuous load (3+ hours — EV charging, water heaters, most lighting) must be limited to 80% of the device: 120 A on this circuit (NEC 210.20(A)). Hot locations or bundled raceways derate the conductor further (310.15) and can push you up a size.
Distance is the other size driver. At 120 A load and 100 ft one-way on 1/0 AWG copper at 240 V, the computed voltage drop is 2.93 V (1.22%) — inside the NEC's recommended 3% (210.19(A) Informational Note).
Run the numbers yourself
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