Wire Sizing

What Size Wire for 100 Amp 100 Feet Away

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

Recommended Wire Size

Copper

3 AWG

Voltage drop: 2.04% (4.9V)

Voltage at load: 235.1V

Controlling factor: Ampacity (NEC 310.16)

Aluminum

1 AWG

Voltage drop: 2.11% (5.06V)

Voltage at load: 234.9V

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	62.8V	26.17%	177.2V
12 AWG	20A	39.6V	16.5%	200.4V
10 AWG	30A	24.8V	10.33%	215.2V
8 AWG	50A	15.56V	6.48%	224.4V
6 AWG	65A	9.82V	4.09%	230.2V
4 AWG	85A	6.16V	2.57%	233.8V
3 AWGREC	100A	4.9V	2.04%	235.1V
2 AWG	115A	3.88V	1.62%	236.1V
1 AWG	130A	3.08V	1.28%	236.9V
1/0 AWG	150A	2.44V	1.02%	237.6V
2/0 AWG	175A	1.93V	0.81%	238.1V
3/0 AWG	200A	1.53V	0.64%	238.5V
4/0 AWG	230A	1.22V	0.51%	238.8V
250 kcmil	255A	1.03V	0.43%	239V
300 kcmil	285A	0.86V	0.36%	239.1V
350 kcmil	310A	0.73V	0.31%	239.3V
400 kcmil	335A	0.64V	0.27%	239.4V
500 kcmil	380A	0.52V	0.22%	239.5V

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

Key Considerations

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

For a 100A/240V circuit at 100 feet, use 3 AWG copper (2.04% drop) or 1 AWG aluminum. This keeps voltage drop within the NEC-recommended 3% limit.

Can I use aluminum wire for a 100 amp circuit?▾

Yes. Aluminum wire is a cost-effective alternative for larger circuits. For 100A at 100 feet, use 1 AWG aluminum (2.11% 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 100A 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.

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

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