What size wire do I need for a 50 amp breaker?

6 AWG copper is the smallest conductor our model estimates at or above 50 A using a 75 °C insulation rating; 6 AWG is required if the terminations are limited to 60 °C. In aluminium the equivalent is 4 AWG. Verify against the code edition adopted locally before installing.

Can I use aluminium wire on a 50 amp circuit?

Yes, where the terminations are rated for aluminium. Because aluminium carries roughly 78% of the current of the same copper size, a 50 A circuit steps up to 4 AWG and uses K = 21.2 in the voltage-drop formula instead of 12.9.

How far can a 50 amp circuit run?

On 6 AWG copper the 3% voltage-drop guideline is reached near 73 ft one-way at 120 V and 146 ft at 240 V. Longer runs need the next size or two up — length, not ampacity, decides most feeder sizes.

Is a 50 amp breaker sized at 100% of the load?

Only for non-continuous loads. A continuous load is designed at 125%, so 50 A of continuous current becomes 62.5 A of design current and lands on a 70 A device with conductors sized to match.

What is typically on a 50 amp circuit?

Commonly electric ranges, welders, 40 A EV chargers, hot tubs. The load type also drives the receptacle and disconnect ratings, not just the conductor size.

What Size Wire for a 50 Amp Breaker?

Conductor size, aluminium equivalent, derating and maximum run length for a 50 amp circuit — all derived from published conductor geometry and the voltage-drop formula.

Quick answer

A 50 amp circuit needs 6 AWG copper with 75 °C terminations, or 4 AWG aluminium. 6 AWG copper applies where equipment terminals are limited to 60 °C. Voltage drop reaches 3% at roughly 146 ft one-way on 240 V and 73 ft on 120 V.

Formula estimate

Copper @ 75 °C

6 AWG

Copper @ 60 °C

6 AWG

Aluminium @ 75 °C

4 AWG

3% drop @ 240 V

146ft

Conductor options for 50 A

Estimated ampacity of each candidate size, so you can see the margin you are buying.

Material / rating	Minimum size	Estimated ampacity	Margin over 50 A
Copper, 60 °C	6 AWG	50 A	+0 A
Copper, 75 °C	6 AWG	59 A	+9 A
Copper, 90 °C	6 AWG	67 A	+17 A
Aluminium, 75 °C	4 AWG	62 A	+12 A
Aluminium, 90 °C	6 AWG	52 A	+2 A

Ampacity estimated as I = 0.0670 × cmil^0.6505, scaled for insulation rating and material.

Source & method: Conductor areas come from the ASTM B258 relationship d = 5 × 92^((36 − n) / 39). Ampacity is a fitted physical model, not a reproduction of any code table, and runs within roughly ±8% of published values.

Maximum run length on 6 AWG copper

One-way distance before voltage drop passes the 3% and 5% guidelines.

System	3% limit	5% limit	Drop @ 100 ft
120 V 1Ø	73 ft	122 ft	4.1%
240 V 1Ø	146 ft	244 ft	2.05%
208 V 3Ø	146 ft	244 ft	2.05%
480 V 3Ø	338 ft	563 ft	0.89%

Source & method: VD = 2 × K × I × L / cmil single phase, 1.732 × K × I × L / cmil three phase, with K = 12.9 for copper. 6 AWG is 26,251 circular mils and 0.3951 Ω per 1000 ft at 20 °C.

Hot attics, conduit runs and bundling

What a 50 A circuit actually needs once ambient temperature and conductor count are applied.

Ambient	3 conductors	4–6 conductors	7–9 conductors
30 °C	6 AWG	4 AWG	4 AWG
40 °C	6 AWG	4 AWG	3 AWG
50 °C	4 AWG	3 AWG	2 AWG
60 °C	3 AWG	1 AWG	1 AWG

Source & method: Ambient correction F = √((Tc − Ta) / (Tc − 30)) with Tc = 75 °C; bundling adjustment uses the standard stepped schedule (1.00 / 0.80 / 0.70). The conductor shown is the smallest copper size whose corrected ampacity still carries 50 A.

Continuous loads

A continuous load — one expected to run three hours or more, like commercial lighting or an EV charger — is designed at 125% of the load current. 50 A continuous becomes 62.5 A of design current, which lands on a 70 A overcurrent device and 4 AWG copper.

Frequently asked

What size wire do I need for a 50 amp breaker?: 6 AWG copper is the smallest conductor our model estimates at or above 50 A using a 75 °C insulation rating; 6 AWG is required if the terminations are limited to 60 °C. In aluminium the equivalent is 4 AWG. Verify against the code edition adopted locally before installing.
Can I use aluminium wire on a 50 amp circuit?: Yes, where the terminations are rated for aluminium. Because aluminium carries roughly 78% of the current of the same copper size, a 50 A circuit steps up to 4 AWG and uses K = 21.2 in the voltage-drop formula instead of 12.9.
How far can a 50 amp circuit run?: On 6 AWG copper the 3% voltage-drop guideline is reached near 73 ft one-way at 120 V and 146 ft at 240 V. Longer runs need the next size or two up — length, not ampacity, decides most feeder sizes.
Is a 50 amp breaker sized at 100% of the load?: Only for non-continuous loads. A continuous load is designed at 125%, so 50 A of continuous current becomes 62.5 A of design current and lands on a 70 A device with conductors sized to match.
What is typically on a 50 amp circuit?: Commonly electric ranges, welders, 40 A EV chargers, hot tubs. The load type also drives the receptacle and disconnect ratings, not just the conductor size.

Wire and breakers for a 50 A circuit

6 AWG copper wire

Matched to the 50 A sizing on this page.

Affiliate

Links go to Amazon search results, not a single listing — confirm ratings, insulation type and listing details before buying, and make sure the part is approved for your application.