How do you size wire for solar panels?

Start with module short-circuit current and the number of parallel strings, apply the required PV current factor, then check conductor ampacity and voltage drop for the actual one-way run length.

Why does solar wire size depend so much on voltage?

The same voltage drop in volts is a much larger percentage on a 12 volt battery system than on a 300 or 600 volt PV string, so low-voltage solar runs often need much larger conductors.

Can this calculator replace local PV code review?

No. It is a planning tool. PV conductor sizing must also account for module instructions, temperature correction, rooftop conduit conditions, equipment terminals, grounding, protection, and the locally adopted electrical code.

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PV Wire Tool

Solar Wire Size Calculator

// SIZE PV SOURCE AND OUTPUT CONDUCTORS FROM MODULE ISC, PARALLEL STRINGS, RUN LENGTH, VOLTAGE, AMPACITY MARGIN, AND VOLTAGE-DROP TARGET //

PV_INPUTS

Module Isc

Use the short-circuit current from the module nameplate.

Parallel strings

Count strings combined on this conductor segment.

Nominal DC system voltage

One-way run length

Distance from array combiner to controller, inverter, or disconnect.

Voltage-drop target

Material

Terminal rating

Current factor

PV_SIZE_RESULT

Recommended minimum

8 AWG

8.4 mm², passing ampacity and 3% voltage drop.

Estimated drop

2.28%

3.42 V at the PV design current.

Array Isc

22.4 A

Required ampacity

34.9 A

Drop current

28.0 A

This is a planning minimum. Verify conductor insulation, wet-location rating, rooftop temperature correction, terminal ratings, and overcurrent protection before installation.

14 AWG

2.1 mm²

Ampacity

20.0 A

Drop

9.17%

Status

12 AWG

3.3 mm²

Ampacity

25.0 A

Drop

5.76%

Status

10 AWG

5.3 mm²

Ampacity

35.0 A

Drop

3.61%

Status

8 AWG

8.4 mm²

Ampacity

50.0 A

Drop

2.28%

Status

Pass

6 AWG

13.3 mm²

Ampacity

65.0 A

Drop

1.47%

Status

Pass

4 AWG

21.1 mm²

Ampacity

85.0 A

Drop

0.92%

Status

Pass

3 AWG

26.7 mm²

Ampacity

100 A

Drop

0.73%

Status

Pass

2 AWG

33.6 mm²

Ampacity

115 A

Drop

0.58%

Status

Pass

1 AWG

42.4 mm²

Ampacity

130 A

Drop

0.46%

Status

Pass

1/0 AWG

53.5 mm²

Ampacity

150 A

Drop

0.36%

Status

Pass

2/0 AWG

67.4 mm²

Ampacity

175 A

Drop

0.29%

Status

Pass

3/0 AWG

85.0 mm²

Ampacity

200 A

Drop

0.23%

Status

Pass

4/0 AWG

107.2 mm²

Ampacity

230 A

Drop

0.18%

Status

Pass

PV_CURRENT_BASIS

PV source and output circuits are commonly sized from module short-circuit current, not only operating current.

The 156% option represents a conservative NEC-style planning screen: array Isc times 125%, then another 125% ampacity factor.

Use the 125% option only when your design method, equipment listing, or local code path supports that basis.

VOLTAGE_DROP

Voltage drop is calculated over the round-trip DC conductor path.

Low-voltage battery and charge-controller circuits are much more sensitive to drop than 300 V or 600 V PV strings.

A 2% to 3% target is typical when energy harvest and inverter performance matter.

FIELD_LIMITS

Rooftop conduit, high ambient temperature, and bundled circuits can require additional ampacity correction.

Outdoor PV wiring must use insulation and cable assemblies rated for the actual wet, UV, and temperature exposure.

Always coordinate conductor size with disconnects, fuses, terminals, combiner boxes, and equipment instructions.

RELATED_TOOLS

Voltage Drop Calculator

Check the voltage-drop math directly for long PV source and inverter output runs.

Ampacity Calculator

Review conductor ampacity, temperature ratings, and derating assumptions separately.

Conduit Fill Calculator

Plan raceway fill when PV circuits are grouped in conduit.

Cable Size Calculator

Compare this PV result against a general cable sizing workflow.

Wire Resistance Calculator

Inspect conductor resistance when losses or heat need closer review.

Wire Weight Calculator

Estimate handling weight for long outdoor cable pulls and rooftop runs.