AmpSizerWhat size wire for 50 amps?
8 AWG copper on a 50 amp breaker, with a 10 AWG copper ground — up to about 93 feet at 240 volts. Past that, 6 AWG, because voltage drop rather than ampacity becomes the rule that decides.
8 AWG copper carries exactly 50 amps in the 75 °C column of Table 310.16, which is the column your breaker terminals are listed at. In aluminium the same circuit is 6 AWG.
Two situations change the answer. If the load is continuous — on for three hours or more — the circuit is sized at 62.5 amps rather than 50, and that is 6 AWG copper. And if the conductors share a raceway with more than three current-carrying conductors, derating applies before anything else does.
The answer by distance
At 240 volts, 50 amps, copper, 3% target:
| Run | Conductor | Drop | Why |
|---|---|---|---|
| 25 ft | 8 AWG | 0.8% | Ampacity decides |
| 50 ft | 8 AWG | 1.6% | Ampacity decides |
| 75 ft | 8 AWG | 2.4% | Ampacity decides |
| 93 ft | 8 AWG | 3.0% | The crossover |
| 100 ft | 6 AWG | 2.0% | Voltage drop decides |
| 150 ft | 6 AWG | 3.1% | Just over — 4 AWG for margin |
| 200 ft | 4 AWG | 2.6% | Voltage drop decides |
Halve every distance for a 120 volt circuit. The crossover at 120 V is about 46 feet, which is why 50 amp circuits at 120 volts are rare and unpleasant.
What a 50 amp circuit usually feeds
| Load | Neutral needed | Continuous | Typical conductor |
|---|---|---|---|
| Electric range | Yes | No | 8 AWG or 6/3 NM |
| Hot tub or spa | Usually | No | 8 AWG in PVC |
| 40 A EV charger | No | Yes | 8 AWG, 50 A breaker |
| Welder | No | No | 8 AWG |
| Sub panel | Yes | No | 8 AWG plus neutral and ground |
| RV receptacle, 14-50R | Yes | No | 8 AWG, four conductors |
The EV charger row is the one that catches people. A 40 amp charger on a 50 amp breaker is correct — 40 × 1.25 is 50 — and a 50 amp charger on a 50 amp breaker is not.
The three ways a 50 amp circuit goes wrong
Cable instead of conductors. 8/3 NM cable is a 40 amp cable because of the 60 °C rule, while 8 AWG THHN in conduit is 50. If the plan says Romex, the size goes up.
Aluminium sized like copper. 8 AWG aluminium is 40 A at 75 °C. The aluminium answer for 50 amps is 6 AWG.
Forgetting the run is long. A garage, a shop or a spa at the end of the garden is where the 3% target starts to matter, and where nobody checks it — the wire carries the current perfectly and the equipment behaves as if something is wrong with it.
Work out your own case on the wire size calculator, which does both rules at once and tells you which one decided.
Frequently asked questions
What size wire for 50 amps 100 feet away?
6 AWG copper at 240 volts. At 100 ft, 8 AWG drops 3.2% and 6 AWG drops 2.0%, so the 3% target is what forces the step up. On a 120 volt circuit at the same distance the answer moves to 4 AWG, because the same volts lost are twice the percentage.
Can I use 8 gauge for a 50 amp breaker?
Yes, on a short run with a non-continuous load, because 8 AWG copper is 50 A at 75 °C. It is right at the limit rather than comfortably inside it, which is why many electricians pull 6 AWG for 50 amp circuits by habit — it costs a little more and removes the question.
What size wire for a 50 amp RV plug?
8 AWG copper for the two hots and the neutral with a 10 AWG ground, or 6 AWG on a long run. A 14-50R receptacle is a four-wire device — two hots, a neutral and a ground — because the coach runs 120 volt circuits from each leg. Three conductors will not do, even though the pedestal only needs 240 volts.
Is a 50 amp circuit 6/3 or 8/3 cable?
8/3 NM cable is rated 40 amps, not 50, because non-metallic sheathed cable uses the 60 °C column under 334.80 — so a 50 amp circuit in NM cable needs 6/3. In conduit with THHN or THWN-2 conductors the 75 °C column applies and 8 AWG is fine. Same copper, different rating, because of the sheath.
Does a 50 amp circuit need a neutral?
Only if something on it uses 120 volts. A range or an RV receptacle does and needs four conductors. A hot tub usually does. A welder, an EV charger or a straightforward 240 volt heater does not, and three conductors is correct — two hots and a ground.
How we calculate this
2 × amps × R × one-way feet ÷ 1,000 on the Chapter 9 Table 8 resistance of 0.778 ohms per 1,000 ft
for 8 AWG and 0.491 for 6 AWG, against a 3% target — which puts the crossover at about 93 ft on 240 volts and
46 ft on 120. The equipment grounding conductor is 10 AWG from Table 250.122. Non-metallic sheathed cable is
restricted to the 60 °C column by 334.80, which is why 8/3 NM is a 40 amp cable.Sources: