What gauge wire for solar panels?

It depends on the current (amps) and wire distance. For a typical residential string of 2–3 panels producing 10–15 amps, 10 AWG wire is sufficient for runs under 30 feet. For higher-current parallel arrays (20–40 amps), you need 8–6 AWG. Use the calculator above with your specific amps and distance for an exact answer.

What size wire from charge controller to battery?

This is the highest-current, shortest run in most systems. For a 30A controller at 5 feet: 10 AWG. For 50A at 5 feet: 8 AWG. For 80A at 3 feet: 6 AWG. Keep this run as short as possible (under 6 feet) to minimize voltage drop and allow thinner wire. At 12V, every foot of wire matters because the voltage tolerance is only 0.36V at 3% drop.

What size cable from solar panel to inverter?

For grid-tied string inverters, the DC side carries high voltage (200–600V) and low current (5–15A), so 10–12 AWG is typically sufficient. For microinverters, the AC branch circuit is 240V at 15–20A, requiring 12–10 AWG per NEC. For off-grid with a battery inverter, size the battery-to-inverter cable for the inverter's full current draw.

What is acceptable voltage drop for solar?

3% is the standard maximum for solar circuits. 2% is ideal for critical runs (controller-to-battery). 5% is acceptable for very long, non-critical runs where the cost of thicker wire is prohibitive. Every 1% of voltage drop equals 1% of energy lost as heat in the wire. At 3% drop on a 10 kW system, you lose 300W continuously during peak production.

Can I use regular copper wire for solar?

For indoor runs (controller to battery, inverter to panel), standard THHN/THWN copper wire in conduit is fine. For outdoor exposed runs (roof, panels to junction box), use PV wire (also called USE-2 or PV-rated cable) which is UV-resistant, sunlight-rated, and has a thicker jacket. PV wire is designed to withstand 30+ years of outdoor exposure.

PV wire (photovoltaic wire) is a single-conductor cable designed specifically for solar installations. It is rated for 600V or 2000V DC, UV-resistant, sunlight-stable for 30+ years, and has a robust insulation jacket that resists abrasion, moisture, and temperature extremes (-40°C to 90°C). USE-2 and PV wire are interchangeable for most solar applications. Standard PV wire costs $0.30–$1.00 per foot depending on gauge.

How do I calculate cable size for a solar system?

Use the VDI (Voltage Drop Index) formula: VDI = amps x one-way distance (feet) / (voltage drop % x system voltage). Example: 30A, 20 ft, 12V system, 3% drop: VDI = 30 x 20 / (3 x 12) = 16.7. Look up 16.7 in the VDI-to-AWG table: 16.7 falls in the 6 AWG range. Or use our calculator above for instant results.

What size conduit for solar wire?

Conduit size depends on the number and gauge of wires. NEC Chapter 9, Table 1 limits conduit fill to 40% for 3+ conductors. Two 10 AWG THHN wires fit in 1/2-inch EMT. Four 8 AWG wires need 3/4-inch EMT. Two 4 AWG wires need 3/4-inch EMT. Use an NEC conduit fill calculator for exact sizing with your wire count and gauge.

Solar Wire Size Calculator: Find The Right AWG For Your Solar System

Undersized wire is a fire hazard. Oversized wire wastes money. This calculator gives you the exact AWG gauge for any solar circuit based on current, distance, and voltage. It also calculates voltage drop, power loss, and fuse size. The rule: keep voltage drop under 3 % of system voltage. At 12V that is only 0.36V of tolerance — every foot of wire and every amp of current matters.

Solar Wire Size Calculator

Enter the current (amps), one-way wire distance (feet), system voltage, and maximum acceptable voltage drop. The calculator returns the recommended AWG gauge, actual voltage drop, power loss, wire ampacity, and fuse size.

Wire Run Specifications

Current (amps)

Panel Isc × 1.25, or controller max output

One-way wire distance

feet

From source to load (not round-trip)

System voltage

Max voltage drop

Recommended wire gauge

6AWG

30A over 15 ft at 12V — voltage drop: 0.356V (2.96%)

For extra safety margin, use 8 AWG (one size thicker)

Voltage drop

0.356V

2.96% of 12V (max 3%)

Power lost in wire

10.67W

0.356V × 30A = heat in wire

Wire ampacity

55A

NEC 310.16 at 75°C (6 AWG)

Fuse / breaker size

40A

30A × 1.25 = 38A → next std size

Round-trip distance

30ft

15 ft × 2 (positive + negative)

Wire resistance

0.3951Ω/1000ft

6 AWG copper at 20°C

How To Wire Solar Panels MPPT vs PWM Controller Connect Panels To Battery

Solar Wire Size Quick Reference

For the most common solar circuits at 3 % maximum voltage drop:

12V System

Amps	5 ft	10 ft	15 ft	20 ft	25 ft	30 ft
10 A	14 AWG	12 AWG	10 AWG	10 AWG	8 AWG	8 AWG
15 A	12 AWG	10 AWG	8 AWG	8 AWG	6 AWG	6 AWG
20 A	10 AWG	8 AWG	8 AWG	6 AWG	6 AWG	4 AWG
30 A	10 AWG	8 AWG	6 AWG	6 AWG	4 AWG	4 AWG
40 A	8 AWG	6 AWG	4 AWG	4 AWG	3 AWG	2 AWG
50 A	8 AWG	6 AWG	4 AWG	2 AWG	2 AWG	1 AWG
80 A	6 AWG	4 AWG	2 AWG	1 AWG	1/0 AWG	1/0 AWG
100 A	4 AWG	2 AWG	1 AWG	1/0 AWG	2/0 AWG	2/0 AWG

48V System (Same Power, Much Thinner Wire)

Amps	5 ft	10 ft	15 ft	20 ft	25 ft	30 ft
10 A	14 AWG	14 AWG	14 AWG	14 AWG	14 AWG	12 AWG
20 A	14 AWG	14 AWG	12 AWG	12 AWG	10 AWG	10 AWG
30 A	14 AWG	12 AWG	10 AWG	10 AWG	10 AWG	8 AWG
50 A	12 AWG	10 AWG	10 AWG	8 AWG	8 AWG	6 AWG
100 A	10 AWG	8 AWG	6 AWG	6 AWG	4 AWG	4 AWG

The 48V advantage is clear. A 30A circuit at 20 ft needs 6 AWG at 12V but only 10 AWG at 48V. That is roughly 4× less copper, 4× cheaper wire. This is the strongest argument for series wiring with an MPPT controller — higher voltage means thinner, cheaper wire with less energy loss.

Wire Size By Solar System Component

Wire run	Typical amps	Typical distance	Recommended AWG	Notes
Panels → combiner box	8–15 A per string	5–50 ft	10–12 AWG PV wire	Use outdoor PV wire (UV rated)
Combiner → charge controller	15–60 A	5–30 ft	8–4 AWG	Keep as short as practical
Controller → battery	20–100 A	3–6 ft	6–2 AWG	Shortest possible — highest current
Battery → inverter	40–200+ A	3–6 ft	4 AWG–2/0 AWG	Shortest possible — highest current at low voltage
Inverter → main panel (AC)	20–50 A	10–50 ft	10–6 AWG (NEC)	Follow local electrical code
Battery interconnects	Same as controller	1–3 ft	Same as controller-battery	Equal length for balanced current

The controller-to-battery and battery-to-inverter runs are critical. These carry the highest current at the lowest voltage (12V or 48V). Mount the charge controller within arm's reach of the battery bank, and the inverter as close to the battery as possible. Every extra foot of cable at these connections costs efficiency and requires thicker (more expensive) wire.

See How To Connect Solar Panels To A Battery for the complete wiring guide and How To Wire Solar Panels for series vs parallel configurations.

The Wire Sizing Formula

The VDI (Voltage Drop Index) method makes wire sizing simple:

VDI = Amps × Distance (one-way ft) ÷ (% Drop × Voltage)

Then match VDI to AWG:

VDI range	AWG
0–2	14
2–3	12
3–5	10
5–8	8
8–13	6
13–21	4
21–26	3
26–33	2
33–42	1
42–53	1/0
53–67	2/0
67–84	3/0
84–107	4/0

Worked example: 30A, 20 ft, 12V system, 3 % drop

VDI = 30 × 20 ÷ (3 × 12) = 600 ÷ 36 = 16.7

VDI 16.7 falls in the 13–21 range → 4 AWG.

Same circuit at 48V:

VDI = 7.5 × 20 ÷ (3 × 48) = 150 ÷ 144 = 1.04

VDI 1.04 → 14 AWG. Same power, dramatically thinner wire.

Why Voltage Drop Matters

Every percent of voltage drop is a percent of energy lost as heat in the wire:

Voltage drop	Energy lost	8 kW system loss	Annual cost at $0.16/kWh
1 %	1 %	80 W	$47/year
2 %	2 %	160 W	$94/year
3 % (standard max)	3 %	240 W	$140/year
5 %	5 %	400 W	$234/year

At 12V, 3 % voltage drop is only 0.36V — thinner wire at long distances easily exceeds this. At 48V, 3 % is 1.44V — much more forgiving. This is why every serious home solar system uses 24V or 48V, and why MPPT charge controllers (which handle higher voltage from series-wired panels) are worth the premium.

Fuse And Disconnect Sizing

Location	Fuse rating	Purpose
Panel string output	1.25 × Isc of string	Protect wire and controller
Controller → battery	Controller max output A	Protect battery cable
Battery → inverter	Inverter max input A	Protect against short circuit
DC disconnect (grid-tied)	System max current	NEC-required safety shutoff

The 1.25× safety factor (NEC 690.8) accounts for continuous load conditions. Solar circuits are considered continuous loads because they can produce at maximum for 3+ hours continuously.

Common Misreadings

"I can use any copper wire." For outdoor exposed runs (roof, panel arrays), you must use PV-rated wire (USE-2) that is UV-resistant and sunlight-stable. Standard THHN degrades in direct sunlight within a few years.
"Voltage drop doesn't matter on short runs." It matters less, but the controller-to-battery run at 12V carries very high current. Even a 3-foot run at 100A through undersized wire can overheat.
"Bigger wire is always better." Oversized wire wastes money (copper is expensive) and is harder to route through conduit. Size correctly with the calculator and add one gauge of safety margin if unsure.
"I can use the same wire gauge for all runs." Each run has different amps and different distance. The panel-to-controller run (low current, long distance) needs different wire than the battery-to-inverter run (very high current, short distance). Size each run independently.

Bottom Line

Use the calculator. Input your amps, distance, and voltage. Get the exact AWG. Keep voltage drop under 3 %. Keep high-current runs (controller-to-battery, battery-to-inverter) as short as possible. Use PV wire for outdoor runs. Fuse every connection at 1.25× continuous current. And if your 12V system requires absurdly thick wire — that is the system telling you to upgrade to 24V or 48V.