What size wire for a 30 amp generator inlet?
This table covers the fixed wiring between a 30 A power inlet and the panel, for a generator drawing 24 A at 240 V (5760 W, which is 80% of the inlet rating, the usual continuous limit). The breaker comes out at 30 A, 2-pole (24 A x 125%, rounded up to a standard size in NEC 240.6(A)). Every figure below is produced by the same code as our inlet breaker and wire sizer; click one to open the sizer pre-filled with the working shown.
Smallest conductor that passes, by one-way distance
| Distance, inlet to panel | Copper, 30 C ambient (voltage drop) | Aluminum, 30 C ambient | Copper, 40 C (104 F) ambient |
|---|---|---|---|
| 10 ft | 10 AWG (0.2%) | 8 AWG (0.3%) | 10 AWG (0.2%) |
| 25 ft | 10 AWG (0.6%) | 8 AWG (0.6%) | 10 AWG (0.6%) |
| 50 ft | 10 AWG (1.2%) | 8 AWG (1.3%) | 10 AWG (1.2%) |
| 100 ft | 10 AWG (2.4%) | 8 AWG (2.6%) | 10 AWG (2.4%) |
| 150 ft | 8 AWG (2.3%) | 6 AWG (2.4%) | 8 AWG (2.3%) |
Basis: 2023 NEC. Ampacity from Table 310.16, 75 C column (terminations, 110.14(C)), corrected with Table 310.15(B)(1) for ambient air, never below the 30 A breaker, and within the 240.4(D) small conductor limits. Voltage drop from Chapter 9 Table 8 resistance at 240 V with a 3% target (a recommendation from 210.19 informational notes, not a mandate). Size is AWG, or kcmil from 250 up. Add an equipment grounding conductor per Table 250.122 and a neutral if the inlet is 4-wire. Results round to the safe side.
How to read it
At short distances ampacity decides the size. As the run gets longer, voltage drop forces a bigger conductor than ampacity alone would. A hot attic or sunlit conduit raises the ambient figure and can also push the size up, which is what the last column shows. This table is for the fixed run only. The portable cord from generator to inlet is a different question; use the inlet and cord matcher.
Safety
An inlet must feed the panel through an interlock kit or a transfer switch, never a double-ended cord or a dryer outlet. Local amendments apply, and the work needs a licensed electrician and a permit where required. Your inspector decides the final wire and conduit.
Open the wire and breaker sizer Match the inlet and cord
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