Wire Sizing

Wire Size for HVAC Unit — 20 Amp 50 Feet

Pre-calculated NEC-compliant wire size for 20 amps at 50 feet on a 240V single-phase circuit. Immediate answer below.

Recommended Wire Size

Copper

12 AWG

Voltage drop: 1.65% (3.96V)

Voltage at load: 236V

Controlling factor: Ampacity (NEC 310.16)

Aluminum

10 AWG

Voltage drop: 1.7% (4.08V)

Voltage at load: 235.9V

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 50 ft.

Wire Comparison Table

Wire Size	Ampacity	V-Drop (V)	V-Drop (%)	V at Load
14 AWG	15A	6.28V	2.62%	233.7V
12 AWGREC	20A	3.96V	1.65%	236V
10 AWG	30A	2.48V	1.03%	237.5V
8 AWG	50A	1.56V	0.65%	238.4V
6 AWG	65A	0.98V	0.41%	239V
4 AWG	85A	0.62V	0.26%	239.4V
3 AWG	100A	0.49V	0.2%	239.5V
2 AWG	115A	0.39V	0.16%	239.6V
1 AWG	130A	0.31V	0.13%	239.7V
1/0 AWG	150A	0.24V	0.1%	239.8V
2/0 AWG	175A	0.19V	0.08%	239.8V
3/0 AWG	200A	0.15V	0.06%	239.8V
4/0 AWG	230A	0.12V	0.05%	239.9V
250 kcmil	255A	0.1V	0.04%	239.9V
300 kcmil	285A	0.09V	0.04%	239.9V
350 kcmil	310A	0.07V	0.03%	239.9V
400 kcmil	335A	0.06V	0.03%	239.9V
500 kcmil	380A	0.05V	0.02%	239.9V

Table shows all standard AWG/kcmil sizes for 20A at 50 ft on 240V (copper). Green check = meets both ampacity and 3% voltage drop. REC = smallest compliant size.

Key Considerations

For a 20A circuit at 50 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 50 feet?▾

For a 20A/240V circuit at 50 feet, use 12 AWG copper (1.65% drop) or 10 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 50 feet, use 10 AWG aluminum (1.7% 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 50 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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Need a Custom Calculation?

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

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