| Item | Value |
|---|---|
| Breaker type | Double-pole, 240 V |
| Recommended copper conductor | 8 AWG |
| Recommended aluminum conductor | 6 AWG |
| Minimum per NEC Table 310.16, 75°C | 8 AWG copper (50 A) |
| Minimum NM-B cable, 60°C column | 8 AWG copper (40 A) |
| Equipment grounding conductor | 10 AWG copper / 8 AWG aluminum (NEC Table 250.122) |
| Maximum continuous load (125% rule) | 32 A |
| Maximum non-continuous load | 40 A |
Electric ranges and cooktops, 32 A Level 2 EV chargers, larger central air conditioning, electric furnaces
| Load | Notes |
|---|---|
| Electric range / cooktop | 40 A is common for cooktops and smaller ranges |
| Level 2 EV charger (32 A) | 32 × 1.25 = 40 A circuit — NEC 625.41 |
| Central air conditioner | Size from the nameplate MCA and MOCP |
| Electric furnace / air handler | Often multiple circuits |
40 A is where the 125% continuous-load rule starts to bite. An EV charger or an electric heater runs for more than three hours, so the circuit must be rated at 125% of the load: a 32 A charger needs a 40 A circuit, not a 32 A one.
Outdoor and garage receptacle outlets up to 250 V require GFCI protection under NEC 210.8(A). Hard-wired appliances are generally exempt unless a specific article requires it.
| One-way run | Drop | % of 240V | Verdict |
|---|---|---|---|
| 25 ft | 1.56 V | 0.6% | Within the 3% branch-circuit target |
| 50 ft | 3.11 V | 1.3% | Within the 3% branch-circuit target |
| 75 ft | 4.67 V | 1.9% | Within the 3% branch-circuit target |
| 100 ft | 6.22 V | 2.6% | Within the 3% branch-circuit target |
| 150 ft | 9.34 V | 3.9% | Over 3% — upsize one gauge |
| 200 ft | 12.45 V | 5.2% | Well over 3% — upsize two gauges or more |
The 80% rule: a continuous load is one expected to run for three hours or more — EV chargers, electric heat, and most commercial lighting. NEC 210.20(A) requires the overcurrent device to be rated at not less than 125% of that continuous load, which leaves 32 A usable on a 40 A breaker. A breaker that trips after an hour or two under a steady load is usually a continuous-load sizing mistake, not a faulty breaker.
8 AWG copper or 6 AWG aluminum, per NEC Table 310.16 at the 75°C column. The equipment grounding conductor is 10 AWG copper per NEC Table 250.122.
32 amps. NEC 210.19(A)(1) and 210.20(A) require the circuit to be rated at 125% of a continuous load — one that runs for three hours or more — which works out to 80% of the breaker rating available for continuous use. Non-continuous loads may use the full 40 A.
10 AWG copper or 8 AWG aluminum, from NEC Table 250.122. The table lists maximum overcurrent device ratings, so you round up to the next listed row. If the circuit conductors are upsized for voltage drop, NEC 250.122(B) requires the ground to be upsized proportionally too.
Yes. NEC 334.80 requires NM-B ampacity to be taken from the 60°C column of Table 310.16, where 8 AWG copper is rated 40 A. That is why NM-B sometimes needs a larger conductor than THHN in conduit for the same breaker.