Solar Fuse Size Calculator

How to use this calculator

Pick the circuit type that matches what you’re protecting:

1. PV string / module — fuse rated at 1.56 × Isc (calculator) — Australian installers should also confirm the result meets the slightly tighter AS/NZS 5033 1.5× Isc minimum and rounds up to a standard size
2. Battery → inverter / load — fuse rated at 1.25 × continuous current (AS/NZS 5139)
3. Inverter DC input — fuse rated at 1.25 × maximum input current
4. Charge controller output — fuse rated at 1.25 × rated continuous output

Standard IEC fuse ratings used in Australia: 6, 10, 16, 20, 25, 32, 40, 50, 63, 80, 100, 125, 160, 200, 250 A. Round up to the next listed size — never down.

The 1.5× vs 1.56× difference — and which applies

AS/NZS 5033:2021 clause 4.3.5 specifies the 1.5 × Isc factor for the minimum string overcurrent device rating. The global IEC 60364-7-712 and NEC 690.9 codes use 1.56× (1.25 × 1.25 — continuous duty × irradiance enhancement).

In practice these almost always round to the same standard fuse:

• Module Isc 11.2 A × 1.5 = 16.8 A → 20 A gPV
• Module Isc 11.2 A × 1.56 = 17.5 A → 20 A gPV

Sizing to 1.56× (the calculator’s default) is always at least as compliant as AS/NZS 5033’s 1.5× minimum, so the calculator’s output is safe for Australian installs. Both must always be cross-checked against the module datasheet’s maximum series fuse rating — usually 15 A, 20 A, or 25 A — and the lower of the two values wins.

Where each fuse goes — typical Australian residential install

A grid-tied PV system with battery storage (the dominant new-build configuration in 2026) has four fused circuits:

1. DC combiner string fuses — one gPV fuse per string when three or more strings parallel. Single-MPPT inverters with two strings typically don’t require per-string fusing if the modules’ reverse current rating allows.
2. Array DC isolator — a switch-disconnector on the roof and another at the inverter. Fuses inside the rooftop isolator are not always required; check the inverter manufacturer’s installation manual.
3. Battery DC isolator — a fused DC isolator between the battery and the hybrid inverter, sized at 1.25× the inverter’s continuous DC current. AS/NZS 5139 requires this to be within 600 mm of the battery for most lithium chemistries.
4. AC isolator — between the inverter and the switchboard, plus the dedicated solar circuit MCB in the switchboard itself. Sized per AS/NZS 3000 Section 4 and the inverter’s continuous AC output current.

The DC voltage rating on every PV-side fuse must equal or exceed the maximum Voc at -10 °C — typically 1000 V DC on residential strings. Battery-side fuses on 48 V systems need at least 80 V DC rating.

Standard fuse ratings — round up always

6, 10, 16, 20, 25, 32, 40, 50, 63, 80, 100, 125, 160, 200, 250, 315, 400, 500 A

A 16.8 A calculated minimum rounds up to 20 A. A 138 A battery-side calculation rounds up to 160 A. Never round down — undersized fuses nuisance-trip on a hot summer afternoon and a Clean Energy Council-accredited installer will fail the install at commissioning.

gPV vs Class T vs NH — which fuse class to specify

Three fuse classes dominate Australian PV practice:

• gPV (AS/NZS 60269 series, equivalent IEC 60269-6) — purpose-built for PV strings. 1000/1500 V DC rating, fast clearing on string faults. Standard for combiner boxes. Brands: Mersen Helio Protect, ETI gPV, Bussmann PV.
• Class T (UL 248-15) — extremely high interrupt rating (20 kA at 160 V DC), fast-acting, the standard battery-to-inverter fuse for 12/24/48 V lithium banks. Brands: Bussmann, Littelfuse, Blue Sea.
• NH gG-DC — European-style cartridge, popular in commercial battery installations and three-phase commercial PV. Higher amperage ratings (up to 1000 A+).

The calculator returns the amperage; you pick the fuse class based on voltage and prospective short-circuit current. For a residential install you’ll almost always end up with gPV on the array side and Class T on the battery side.

Worked examples — Australian residential

Example 1 — 6.6 kW system, 2 strings of 10 panels. Module Isc = 11.5 A.

Per-string ≥ 11.5 × 1.5 = 17.25 A (AS/NZS 5033) → 20 A gPV. With only 2 strings, per-string fusing is generally not required if module reverse current rating allows — but most accredited installers fit them anyway as a defence-in-depth measure.

Example 2 — 5 kW hybrid inverter, 13.5 kWh Tesla Powerwall, 48 V nominal.

Continuous DC = 5000 / (48 × 0.95) = 110 A Fuse ≥ 110 × 1.25 = 137 A → 160 A Class T at the battery terminal.

Example 3 — 60 A MPPT charge controller charging 48 V LiFePO4.

Fuse ≥ 60 × 1.25 = 75 A → 80 A Class T or DC-rated MCB between controller and battery.

Wire sizing has to keep up

A fuse only protects the cable if the cable’s continuous current rating equals or exceeds the fuse rating after de-rating. AS/NZS 3008.1.1 has the current-carrying tables for each cable size and installation method.

For a 20 A PV string fuse, 4 mm² single-core PV cable (rated to AS/NZS 5033) carries 51–55 A in free air — comfortable. For a 160 A battery fuse, you’ll need at least 35 mm² battery cable on short runs and 50 mm² for runs over 1.5 m to keep voltage drop under 1.5%.

Use the wire size calculator to verify both ampacity (continuous current capacity) and voltage drop on the longer DC runs from the array down to the inverter.

CEC commissioning — what gets checked

Clean Energy Council-accredited installers must submit commissioning paperwork to the network operator (Energex, Ausgrid, SA Power Networks, etc.). The DC overcurrent protection section asks for:

1. Fuse current rating — equals or exceeds 1.5 × Isc (AS/NZS 5033) per string.
2. Fuse voltage rating — equals or exceeds the maximum Voc at -10 °C.
3. Fuse breaking capacity — equals or exceeds the prospective short-circuit current.
4. Manufacturer compliance — fuses listed on the CEC-approved component list.
5. Maximum series fuse rating on the module sticker is not exceeded.

Fail any one and the install does not get connected to the grid. STC paperwork for the federal renewable rebate also requires this section to be complete.

Limitations and disclaimer

This calculator returns the next standard fuse rating based on the 1.56× PV / 1.25× battery factors. Australian installers should verify the result meets AS/NZS 5033 clause 4.3.5 (PV) and AS/NZS 5139 (battery storage), and confirm against the manufacturer’s stated maximum series fuse rating on the module and inverter datasheets.

All DC overcurrent protection on grid-tied PV and battery systems must be installed by a CEC-accredited installer with an unrestricted electrical licence in the state where the work is performed. DIY installation on grid-connected systems is not permitted in any Australian state.