What wire size do I need for 240V 30A?

For a 30A 240V circuit, use 10 AWG wire for runs under 50 feet. For longer runs, use 8 AWG to keep voltage drop under 3%. The circuit breaker should be 30A, and the wire must be rated for the full load.

What gauge wire for solar inverter AC output?

Size the AC output wire for 125% of the inverter's rated output current. A 7.6kW 240V inverter outputs 31.7A, requiring design for 39.6A — use 8 AWG for runs up to 75 feet, or 6 AWG for longer runs to stay under 2% voltage drop.

AC Wire Size Calculator

Find the right AWG wire gauge for 120V and 240V AC circuits. Accounts for both ampacity and voltage drop.

Circuit parameters

Current?

Voltage?

One-way distance?

Phase?

Max voltage drop?

Recommended wire size

12 AWG

Voltage drop3.96 V (1.65%)

Maximum allowed drop7.20 V (3%)

AWG	Ampacity	V Drop	Drop %	OK?
14	15A	6.28V	2.6%	✗ Low amp
12	20A	3.96V	1.7%	✓
10	30A	2.48V	1.0%	✓
8	50A	1.56V	0.6%	✓
6	65A	0.98V	0.4%	✓
4	85A	0.62V	0.3%	✓
3	100A	0.49V	0.2%	✓
2	115A	0.39V	0.2%	✓
1	130A	0.31V	0.1%	✓
1/0	150A	0.24V	0.1%	✓
2/0	175A	0.19V	0.1%	✓
3/0	200A	0.15V	0.1%	✓
4/0	230A	0.12V	0.1%	✓

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How to Use This Calculator

Enter your circuit's load current (amps), system voltage (120V or 240V), one-way wire run distance, and phase. The calculator finds the minimum AWG wire size that meets both NEC ampacity requirements and your voltage drop limit.

What is voltage drop?

Voltage drop is the reduction in voltage that occurs when current flows through a wire's resistance. Long runs or thin wires cause excessive voltage drop, reducing efficiency and potentially causing motors and appliances to run hot. The NEC recommends a maximum of 3% voltage drop for branch circuits and 2% for feeders.

Solar inverter circuits

For the AC output circuit from a solar inverter to the main panel, size wire for the inverter's rated output current. A 7.6kW 240V inverter outputs about 32A — use 8 AWG wire for runs up to 100 feet to keep voltage drop under 2%.

The Formula

Single-phase: V_drop = 2 × distance (ft) × current (A) × resistance (Ω/1000ft) ÷ 1000 Three-phase: V_drop = √3 × distance (ft) × current (A) × resistance (Ω/1000ft) ÷ 1000 Drop % = (V_drop ÷ system voltage) × 100 NEC ampacity rule: wire must be rated for at least 125% of continuous load

The "2×" factor for single-phase accounts for both the hot conductor and the neutral return path. Three-phase circuits use the square root of 3 (1.732) because the three phases partially cancel each other.

AWG Wire Size Quick Reference

14 AWG15A max — lighting and receptacles

12 AWG20A max — kitchen outlets, appliances

10 AWG30A max — dryers, EV Level 1, small A/C

8 AWG40-50A max — solar inverters, large A/C

6 AWG55-65A max — EV chargers (48A), subpanels

4 AWG70-85A max — large subpanels, commercial solar

FAQ

What wire size do I need for a solar inverter? ▼

Size the AC output wire for 125% of the inverter's rated output current. A 5kW 240V inverter outputs 20.8A — design for 26A, use 10 AWG for short runs. A 7.6kW 240V inverter outputs 31.7A — design for 39.6A, use 8 AWG. For runs over 50 feet, check voltage drop and upsize to 6 AWG to keep drop under 2%.

What is the NEC 80% rule for wire sizing? ▼

The NEC 80% rule (or 125% rule stated differently) says that continuous loads — loads that operate for 3 hours or more — must not exceed 80% of the circuit breaker rating. A 20A breaker should not have more than 16A of continuous load. This is why the calculator multiplies your load current by 1.25 to find the design current for wire sizing.

Does wire gauge affect solar efficiency? ▼

Yes. Every 1% of voltage drop means 1% less power reaching your loads or the grid. For a 7.6kW solar system, a 3% voltage drop wastes 228W — that's real money over the system's 25-year life. Upsizing from 10 AWG to 8 AWG for a 50-foot run typically costs $30-50 in extra wire but saves thousands in lost production over the system lifetime.

120V vs 240V — which requires larger wire? ▼

For the same power, 240V circuits use half the current of 120V circuits, which means you can use thinner wire. A 1,200W 120V circuit draws 10A (needs 14 AWG). The same 1,200W at 240V draws only 5A (14 AWG easily handles it). This is why high-power loads like water heaters, dryers, EV chargers, and solar inverters run on 240V — less wire cost and heat.