PV & AC Protection Sizing
Size PV and AC breakers and surge protection.
Free to use without an account. A free installer account adds saved work, A4 previews and branded PDF exports.
The protection sizing tool selects PV and AC cable, breakers, fuses, surge protection and the earth conductor from circuit current, voltage, run length, conductor material and an acceptable voltage drop.
How the PV & AC Protection Sizing works
Choose the circuit
Select the PV DC circuit, inverter-to-board AC, grid-to-inverter or AC surge protection. The calculation changes with the circuit type and number of phases.
Enter current, voltage and run length
Use design current, not nameplate current, and measure the one-way cable run. Long runs need a larger conductor to stay inside the drop limit.
Read the recommendation
The tool returns cable cross-section, voltage drop in volts and percent, cable loss, breaker and fuse rating and the earth conductor size, with warnings when no listed cable is adequate.
Worked example
48 V battery to inverter
100 A design current, 48 V DC, 12 m one-way run, copper conductor, 3% maximum voltage drop.
- 50 mm² copper cable
- About 1.9% voltage drop
- 125 A breaker and fuse
- 16 mm² earth conductor
Assumptions and limits
- Ampacity comes from a fixed reference table. It does not automatically derate for high ambient temperature, conduit grouping or insulation type.
- Breakers and fuses are sized at 1.25× the design current and rounded up to a standard rating.
- The tool does not replace a licensed electrician's final check of fault current, discrimination and local code requirements.
Frequently asked questions
What size cable do I need for a solar system?
Cable size depends on current, conductor material, run length and the acceptable voltage drop. The tool calculates the recommended cross-sectional area and checks ampacity.
Does the tool size both PV and AC protection?
Yes. Choose the circuit type to size PV or AC breakers, fuses and surge protection devices with the relevant voltage and earthing checks.
Why is voltage drop important?
Excessive voltage drop wastes energy and can reduce equipment performance. The calculator keeps the recommended cable within your chosen drop limit.
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Last updated 17 October 2026Maintained by Mishka Energy.
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