☀️ Solar & Battery Wire Size
Solar circuits are tighter than house wiring, and each one takes its current from a different place. Pick the circuit and we ask for the right number.
How we calculated this
Why solar wiring is different
On a branch circuit a 3% drop is a rule of thumb for a load that runs now and then. Solar changes both halves of that. The loss is continuous, so it compounds into real lost energy, and the voltages are low, so a small percentage is a very small number of volts to spend. 1% of 12 V is 0.12 V for the entire out-and-back trip.
Getting the current right
Each of the three circuits takes its current from a different place, and using the wrong one is the easiest way to get a badly wrong answer. Panels are closer to a current source, so their operating current barely moves. A charge controller is rated by what it can put out, which is not what the panels put in. And an inverter's draw climbs as the battery falls, so dividing watts by the nominal bank voltage understates it exactly when the cable can least afford it.
What this tool does not do
This answers voltage drop and nothing else. It does not evaluate ampacity, temperature, overcurrent protection, disconnects, grounding, or code compliance, and it does not handle an inverter's AC output — use the voltage drop calculator for that, which knows about single- and three-phase. Treat the size here as one of two answers you need, and use whichever is larger.