Wire Sizing

Wire Size for Pool Pump — 20 Amp 100 Feet

Pre-calculated NEC-compliant wire size for 20 amps at 100 feet on a 240V single-phase circuit. Immediate answer below.

Recommended Wire Size

Copper

10 AWG

Voltage drop: 2.07% (4.96V)

Voltage at load: 235V

Controlling factor: Voltage Drop (3% limit)

Aluminum

8 AWG

Voltage drop: 2.13% (5.12V)

Voltage at load: 234.9V

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 100 ft.

Wire Comparison Table

Wire Size	Ampacity	V-Drop (V)	V-Drop (%)	V at Load
14 AWG	15A	12.56V	5.23%	227.4V
12 AWG	20A	7.92V	3.3%	232.1V
10 AWGREC	30A	4.96V	2.07%	235V
8 AWG	50A	3.11V	1.3%	236.9V
6 AWG	65A	1.96V	0.82%	238V
4 AWG	85A	1.23V	0.51%	238.8V
3 AWG	100A	0.98V	0.41%	239V
2 AWG	115A	0.78V	0.32%	239.2V
1 AWG	130A	0.62V	0.26%	239.4V
1/0 AWG	150A	0.49V	0.2%	239.5V
2/0 AWG	175A	0.39V	0.16%	239.6V
3/0 AWG	200A	0.31V	0.13%	239.7V
4/0 AWG	230A	0.24V	0.1%	239.8V
250 kcmil	255A	0.21V	0.09%	239.8V
300 kcmil	285A	0.17V	0.07%	239.8V
350 kcmil	310A	0.15V	0.06%	239.9V
400 kcmil	335A	0.13V	0.05%	239.9V
500 kcmil	380A	0.1V	0.04%	239.9V

Table shows all standard AWG/kcmil sizes for 20A at 100 ft on 240V (copper). Green check = meets both ampacity and 3% voltage drop. REC = smallest compliant size.

Key Considerations

For a 20A 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 20 amp service at 100 feet?▾

For a 20A/240V circuit at 100 feet, use 10 AWG copper (2.07% drop) or 8 AWG aluminum. This keeps voltage drop within the NEC-recommended 3% limit.

Can I use aluminum wire for a 20 amp circuit?▾

Yes. Aluminum wire is a cost-effective alternative for larger circuits. For 20A at 100 feet, use 8 AWG aluminum (2.13% 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 20A 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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