Wire Sizing

What Size Wire for 40 Amp 150 Feet Away

Pre-calculated NEC-compliant wire size for 40 amps at 150 feet on a 240V single-phase circuit. Immediate answer below.

Recommended Wire Size

Copper

6 AWG

Voltage drop: 2.46% (5.89V)

Voltage at load: 234.1V

Controlling factor: Voltage Drop (3% limit)

Aluminum

4 AWG

Voltage drop: 2.54% (6.1V)

Voltage at load: 233.9V

Controlling factor: Voltage Drop (3% limit)

Based on NEC Table 310.16 (75°C column), single-phase, 240V, 3% max voltage drop, one-way distance 150 ft.

Wire Comparison Table

Wire Size	Ampacity	V-Drop (V)	V-Drop (%)	V at Load
14 AWG	15A	37.68V	15.7%	202.3V
12 AWG	20A	23.76V	9.9%	216.2V
10 AWG	30A	14.88V	6.2%	225.1V
8 AWG	50A	9.34V	3.89%	230.7V
6 AWGREC	65A	5.89V	2.46%	234.1V
4 AWG	85A	3.7V	1.54%	236.3V
3 AWG	100A	2.94V	1.23%	237.1V
2 AWG	115A	2.33V	0.97%	237.7V
1 AWG	130A	1.85V	0.77%	238.2V
1/0 AWG	150A	1.46V	0.61%	238.5V
2/0 AWG	175A	1.16V	0.48%	238.8V
3/0 AWG	200A	0.92V	0.38%	239.1V
4/0 AWG	230A	0.73V	0.3%	239.3V
250 kcmil	255A	0.62V	0.26%	239.4V
300 kcmil	285A	0.51V	0.21%	239.5V
350 kcmil	310A	0.44V	0.18%	239.6V
400 kcmil	335A	0.39V	0.16%	239.6V
500 kcmil	380A	0.31V	0.13%	239.7V

Table shows all standard AWG/kcmil sizes for 40A at 150 ft on 240V (copper). Green check = meets both ampacity and 3% voltage drop. REC = smallest compliant size.

Key Considerations

For a 40A circuit at 150 feet on 240V, both ampacity and voltage drop must be satisfied. NEC recommends keeping the total voltage drop (feeder + branch) under 5%, with no more than 3% on either segment alone.

Copper conductors at 75°C column (THHN/THWN-2) are assumed. If using 60°C terminations, derate the ampacity to the 60°C column values. Verify the temperature rating of your terminals.

Frequently Asked Questions

What size wire do I need for a 40 amp service at 150 feet?▾

For a 40A/240V circuit at 150 feet, use 6 AWG copper (2.46% drop) or 4 AWG aluminum. This keeps voltage drop within the NEC-recommended 3% limit.

Can I use aluminum wire for a 40 amp circuit?▾

Yes. Aluminum wire is a cost-effective alternative for larger circuits. For 40A at 150 feet, use 4 AWG aluminum (2.54% voltage drop). Aluminum requires AL-rated connectors and anti-oxidant compound at all terminations.

What happens if the voltage drop exceeds 3%?▾

Voltage drop above 3% reduces equipment efficiency, can cause motors to overheat, and may violate NEC 210.19(A) Informational Note No. 4. For a 40A circuit at 150 feet on 240V, exceeding 3% means the load receives less than 232.8V, which can damage sensitive electronics and shorten appliance lifespan.

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Wire Size for HVAC Unit — 40 Amp 150 Feet

Need a Custom Calculation?

Different voltage, three-phase, or custom max drop percentage? Use our interactive calculator.

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