Solar Cable Size Calculator

Find the smallest cable that both carries the current and keeps voltage drop inside your limit. Pick the run you are wiring, or enter the circuit yourself. Sizes in AWG or mm2, for DC and for the AC side of an inverter.

NEC tables assume 30 °C. A roof space in summer is 45 to 55 °C.

In the same conduit or cable. Four or more derates them all.

NEC 110.14(C) caps the answer at the terminal's own column: 60°C at 100 A or less unless the equipment is marked otherwise, 75°C above that. 90°C wire may be derated from the 90°C column but never used above the terminal limit.

Start from your system voltage

The calculator preloaded for one bank voltage, with the run-length tables, the three standard runs and the inverter current table worked out at that voltage.

12V wire size 24V wire size 48V wire size

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Get the printable solar cable and fuse charts

DC cable ampacity with the ambient and bundling corrections, how far each size runs at 12, 24 and 48 V, PV string fuse sizes from Isc, and battery-to-inverter current by inverter size. Three pages, made to pin by the battery bank.

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How It Works

Two limits, take the larger

A cable has to satisfy two independent requirements, and the right size is whichever is larger:

  • Ampacity: the cable must be rated to carry the current without overheating, at the chosen termination temperature (60, 75 or 90°C).
  • Voltage drop: over the run length, the drop must stay inside your limit, commonly 3% per leg and 2% on the battery-to-inverter run.

On solar systems voltage drop wins far more often than it does in house wiring. A 48 V DC circuit at 30 A over 40 ft carries the same current as a modest household branch circuit, but has a fifth of the voltage to lose it in. On short, very high-current runs such as battery to inverter, ampacity takes back over.

Sizing the current, not guessing it

For the array-to-controller run, use the short-circuit current of the string (Isc) multiplied by 1.56, which is the NEC 690.8 factor of 1.25 for continuous duty applied twice. For the controller-to-battery run, use the controller's rated output current. For the battery-to-inverter run, use the inverter's continuous watts divided by the battery voltage, then add the surge margin the inverter maker specifies. That last one is nearly always the largest cable in the system.

Worked example

A 3000 W inverter on a 48 V bank draws about 62.5 A continuous, and roughly 70 A once inverter efficiency is allowed for. Over a 6 ft run at a 2% limit, 4 AWG copper carries the current comfortably and holds the drop near 0.6%, so the choice is set by ampacity and by the lug size on the inverter, not by the drop.

Ampacities are reference values for not more than three current-carrying conductors in a standard installation. They do not include ambient-temperature or bundling derating, both of which matter in a hot loft or an engine bay. Local wiring rules take precedence. Verify against the applicable standard.

Frequently Asked Questions

What size cable do I need for my solar panels?

For the panel-to-controller run, size on the string short-circuit current times 1.56 and a 3% drop limit. A typical 48 V string at 30 A over 40 ft lands on 8 AWG or 10 mm2. Most PV extension leads sold with connectors are 10 AWG (6 mm2), which is fine for short runs but often undersized once the array is more than about 30 ft from the controller.

What size cable from battery to inverter?

Take the inverter's continuous watts, divide by the battery voltage, and add about 10% for inverter efficiency. A 3000 W inverter on 48 V needs around 70 A, on 24 V around 140 A, and on 12 V around 280 A. Keep the run as short as physically possible and design it to 2% rather than 3%: this cable is short, thick and expensive, and shortening it by a foot saves more than any other decision in the build.

Why does solar cable end up bigger than house wiring?

Because voltage drop is a percentage of a much smaller number. A 3% budget on a 240 V circuit is 7.2 V; on a 12 V circuit it is 0.36 V. The same physical cable that comfortably feeds a 240 V circuit at 20 A over 50 ft will lose eight times the percentage on a 12 V run at the same current.

Can I use ordinary house cable for DC solar runs?

Not for the exposed parts. Panel interconnects need cable rated for UV, moisture and the temperature under a module, which is what PV wire and H1Z2Z2-K are for. Inside a conduit or a vehicle, the constraints are different again: vehicle and marine installs want fine-stranded, tinned cable that tolerates vibration, not the solid conductor used in buildings. Conductor size is only half the specification.

Does this include derating?

No. The ampacities are base values for a standard installation. Apply ambient-temperature and bundling derating separately, which matters more in solar than in house wiring because cable often runs across a hot roof, through a loft or beside an engine. Follow your local wiring rules.

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Continuous and surge inverter rating from your load, plus the DC input current the battery cable has to carry

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Next standard fuse or breaker size for a PV string, controller or inverter circuit

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