Wire Sizing

Wire Size for HVAC Unit — 30 Amp 75 Feet

Pre-calculated NEC-compliant wire size for 30 amps at 75 feet on a 240V single-phase circuit. Immediate answer below.

Recommended Wire Size

Copper

10 AWG

Voltage drop: 2.33% (5.58V)

Voltage at load: 234.4V

Controlling factor: Ampacity (NEC 310.16)

Aluminum

8 AWG

Voltage drop: 2.4% (5.76V)

Voltage at load: 234.2V

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 75 ft.

Wire Comparison Table

Wire Size	Ampacity	V-Drop (V)	V-Drop (%)	V at Load
14 AWG	15A	14.13V	5.89%	225.9V
12 AWG	20A	8.91V	3.71%	231.1V
10 AWGREC	30A	5.58V	2.33%	234.4V
8 AWG	50A	3.5V	1.46%	236.5V
6 AWG	65A	2.21V	0.92%	237.8V
4 AWG	85A	1.39V	0.58%	238.6V
3 AWG	100A	1.1V	0.46%	238.9V
2 AWG	115A	0.87V	0.36%	239.1V
1 AWG	130A	0.69V	0.29%	239.3V
1/0 AWG	150A	0.55V	0.23%	239.5V
2/0 AWG	175A	0.44V	0.18%	239.6V
3/0 AWG	200A	0.34V	0.14%	239.7V
4/0 AWG	230A	0.27V	0.11%	239.7V
250 kcmil	255A	0.23V	0.1%	239.8V
300 kcmil	285A	0.19V	0.08%	239.8V
350 kcmil	310A	0.17V	0.07%	239.8V
400 kcmil	335A	0.14V	0.06%	239.9V
500 kcmil	380A	0.12V	0.05%	239.9V

Table shows all standard AWG/kcmil sizes for 30A at 75 ft on 240V (copper). Green check = meets both ampacity and 3% voltage drop. REC = smallest compliant size.

Key Considerations

For a 30A circuit at 75 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 30 amp service at 75 feet?▾

For a 30A/240V circuit at 75 feet, use 10 AWG copper (2.33% drop) or 8 AWG aluminum. This keeps voltage drop within the NEC-recommended 3% limit.

Can I use aluminum wire for a 30 amp circuit?▾

Yes. Aluminum wire is a cost-effective alternative for larger circuits. For 30A at 75 feet, use 8 AWG aluminum (2.4% 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 30A circuit at 75 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

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What Size Wire for 30 Amp 50 Feet Away

30A / 150 ft

What Size Wire for 30 Amp 150 Feet Away

Need a Custom Calculation?

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

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