Wire Sizing

Wire Size for Well Pump — 15 Amp 100 Feet

Pre-calculated NEC-compliant wire size for 15 amps at 100 feet on a 120V single-phase circuit. Immediate answer below.

Recommended Wire Size

Copper

8 AWG

Voltage drop: 1.95% (2.33V)

Voltage at load: 117.7V

Controlling factor: Voltage Drop (3% limit)

Aluminum

6 AWG

Voltage drop: 2.02% (2.42V)

Voltage at load: 117.6V

Controlling factor: Voltage Drop (3% limit)

Based on NEC Table 310.16 (75°C column), single-phase, 120V, 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	9.42V	7.85%	110.6V
12 AWG	20A	5.94V	4.95%	114.1V
10 AWG	30A	3.72V	3.1%	116.3V
8 AWGREC	50A	2.33V	1.95%	117.7V
6 AWG	65A	1.47V	1.23%	118.5V
4 AWG	85A	0.92V	0.77%	119.1V
3 AWG	100A	0.74V	0.61%	119.3V
2 AWG	115A	0.58V	0.48%	119.4V
1 AWG	130A	0.46V	0.39%	119.5V
1/0 AWG	150A	0.37V	0.3%	119.6V
2/0 AWG	175A	0.29V	0.24%	119.7V
3/0 AWG	200A	0.23V	0.19%	119.8V
4/0 AWG	230A	0.18V	0.15%	119.8V
250 kcmil	255A	0.15V	0.13%	119.8V
300 kcmil	285A	0.13V	0.11%	119.9V
350 kcmil	310A	0.11V	0.09%	119.9V
400 kcmil	335A	0.1V	0.08%	119.9V
500 kcmil	380A	0.08V	0.06%	119.9V

Table shows all standard AWG/kcmil sizes for 15A at 100 ft on 120V (copper). Green check = meets both ampacity and 3% voltage drop. REC = smallest compliant size.

Key Considerations

For a 15A circuit at 100 feet on 120V, 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 15 amp service at 100 feet?▾

For a 15A/120V circuit at 100 feet, use 8 AWG copper (1.95% drop) or 6 AWG aluminum. This keeps voltage drop within the NEC-recommended 3% limit.

Can I use aluminum wire for a 15 amp circuit?▾

Yes. Aluminum wire is a cost-effective alternative for larger circuits. For 15A at 100 feet, use 6 AWG aluminum (2.02% 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 15A circuit at 100 feet on 120V, exceeding 3% means the load receives less than 116.4V, which can damage sensitive electronics and shorten appliance lifespan.

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Need a Custom Calculation?

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

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