225 Amp Wire Size
What size wire for a 225 A subpanel, feeder or circuit? Above 100 A the terminations are 75 °C, so one column decides. Copper and aluminum, with continuous loads, under NEC 2023 & 2026.
Updated
Values are the same in NEC 2023 and NEC 2026. 215.2(A)(1) in 2023, 215.4(A)(1) in 2026.
For reference only. Always verify with the NEC edition adopted by your AHJ.
Wire size for a 225 A circuit or feeder
Above 100 A, 110.14(C)(1)(b) sets the termination provisions of the equipment at 75 °C: use 75 °C conductors, or higher-rated conductors at no more than their 75 °C ampacity. So there is one column to read, the 75 °C column of Table 310.16, not the 60 °C column that applies at 100 A and below. The sizes are for 90 °C insulation (such as THHN), 30 °C ambient and no more than 3 current-carrying conductors. This is the answer for a subpanel feeder or any other 225 A circuit.
| Conductor | 75 °C column (110.14(C)(1)(b)) |
|---|---|
| Copper | 4/0 AWG |
| Aluminum | 300 kcmil |
If 225 A is a continuous load
A continuous load runs three hours or more. 210.19(A)(1) and 215.2(A)(1) size the conductor at 125%, so 225 A becomes 281.25 A.
| Conductor | 75 °C column (110.14(C)(1)(b)) |
|---|---|
| Copper | 300 kcmil |
| Aluminum | 500 kcmil |
What these answers leave out
- Ambient above 30 °C (310.15(B)(1)) and more than 3 current-carrying conductors (310.15(C)(1)) reduce ampacity and can raise the size. Use the calculator to include them.
- Equipment listed and identified for higher-rated conductors may allow more; check the equipment markings.
- Voltage drop is not included; long runs may need a larger conductor.
225 amp wire size questions
- What size wire is needed for a 225 A circuit or subpanel feeder?
- For a 225 A noncontinuous load (90 °C insulation, 30 °C ambient, 3 or fewer current-carrying conductors) read from the 75 °C column of Table 310.16: 4/0 AWG copper or 300 kcmil aluminum. Voltage drop is not included; long runs may need a larger conductor.
- Why is there no 60 °C answer for 225 A?
- Under 110.14(C)(1)(b), termination provisions of equipment for circuits rated over 100 A, or marked for conductors larger than 1 AWG, are used only with conductors rated 75 °C, or with higher-rated conductors whose ampacity does not exceed the 75 °C ampacity (unless the equipment is listed and identified for more). So the 75 °C column of Table 310.16 is the limit, not the 60 °C column that applies at 100 A and below.
- Does a continuous load change the wire size for 225 amps?
- Yes. A continuous load (3 hours or more) is sized at 125% under 210.19(A)(1) and 215.2(A)(1) in NEC 2023, 215.4(A)(1) in NEC 2026, so 225 A becomes 281.25 A. In copper that is 300 kcmil at 75 °C; in aluminum 500 kcmil. The overcurrent device must be sized to the same 125%.
- Is this the same as 225 amp service wire?
- No. A one-family dwelling service can use the 310.12 allowance for services of 100 A to 400 A, but a 225 A subpanel or feeder is sized from Table 310.16 as shown here unless it is a dwelling service or feeder that carries the entire load of the dwelling unit.
Other sizes
You can read the NEC 2023 for free at NFPA free access. Need another load? Use the wire size calculator.