Wire Sizing

What Size Wire for 125 Amp 100 Feet Away

Pre-calculated NEC-compliant wire size for 125 amps at 100 feet on a 240V single-phase circuit. Immediate answer below.

Recommended Wire Size

Copper

1 AWG

Voltage drop: 1.6% (3.85V)

Voltage at load: 236.2V

Controlling factor: Ampacity (NEC 310.16)

Aluminum

2/0 AWG

Voltage drop: 1.66% (3.98V)

Voltage at load: 236V

Controlling factor: Ampacity (NEC 310.16)

Based on NEC Table 310.16 (75°C column), single-phase, 240V, 3% max voltage drop, one-way distance 100 ft.

Wire Comparison Table

Wire Size	Ampacity	V-Drop (V)	V-Drop (%)	V at Load
14 AWG	15A	78.5V	32.71%	161.5V
12 AWG	20A	49.5V	20.63%	190.5V
10 AWG	30A	31V	12.92%	209V
8 AWG	50A	19.45V	8.1%	220.6V
6 AWG	65A	12.28V	5.11%	227.7V
4 AWG	85A	7.7V	3.21%	232.3V
3 AWG	100A	6.13V	2.55%	233.9V
2 AWG	115A	4.85V	2.02%	235.2V
1 AWGREC	130A	3.85V	1.6%	236.2V
1/0 AWG	150A	3.05V	1.27%	237V
2/0 AWG	175A	2.42V	1.01%	237.6V
3/0 AWG	200A	1.91V	0.8%	238.1V
4/0 AWG	230A	1.52V	0.63%	238.5V
250 kcmil	255A	1.29V	0.54%	238.7V
300 kcmil	285A	1.07V	0.45%	238.9V
350 kcmil	310A	0.92V	0.38%	239.1V
400 kcmil	335A	0.8V	0.33%	239.2V
500 kcmil	380A	0.65V	0.27%	239.4V

Table shows all standard AWG/kcmil sizes for 125A at 100 ft on 240V (copper). Green check = meets both ampacity and 3% voltage drop. REC = smallest compliant size.

Key Considerations

For a 125A circuit at 100 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 125 amp service at 100 feet?▾

For a 125A/240V circuit at 100 feet, use 1 AWG copper (1.6% drop) or 2/0 AWG aluminum. This keeps voltage drop within the NEC-recommended 3% limit.

Can I use aluminum wire for a 125 amp circuit?▾

Yes. Aluminum wire is a cost-effective alternative for larger circuits. For 125A at 100 feet, use 2/0 AWG aluminum (1.66% 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 125A circuit at 100 feet on 240V, exceeding 3% means the load receives less than 232.8V, which can damage sensitive electronics and shorten appliance lifespan.

Related Wire Size Calculations

125A / 150 ft

What Size Wire for 125 Amp 150 Feet Away

125A / 200 ft

What Size Wire for 125 Amp 200 Feet Away

125A / 250 ft

What Size Wire for 125 Amp 250 Feet Away

100A / 100 ft

What Size Wire for 100 Amp 100 Feet Away

200A / 100 ft

What Size Wire for 200 Amp 100 Feet Away

Need a Custom Calculation?

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

Wire Size Calculator