AS/NZS Solar PV
Isolator voltage rating, DC arc interruption, and IP rating are three places installers commonly get an AS/NZS 5033 solar DC installation wrong.
AS/NZS 5033 governs PV array installation and safety in Australia and New Zealand, and one of its most safety-critical (and most commonly mis-specified) requirements is the DC isolator on a solar array.
AC current naturally passes through zero 100 or 120 times a second, which is what lets a standard AC switch safely extinguish an arc when it opens under load. DC current never crosses zero — an arc that forms when a DC isolator opens under load will sustain itself unless the device is specifically designed to interrupt DC. Using an AC-rated isolator on a DC solar circuit is a genuine fire risk, not just a paperwork technicality.
| Requirement | Why it matters |
|---|---|
| DC voltage rating ≥ calculated system Voc at minimum temperature | Panel voltage rises in cold weather — the isolator must handle the coldest realistic condition, not just the datasheet STC figure |
| Current rating ≥ 1.25 × array Isc | Same safety margin logic covered in the PV cable sizing article |
| Genuine DC arc interruption rating | Not simply a DC-rated contact — the switching mechanism itself must be designed to extinguish a sustained DC arc |
| IP55 minimum, IP66 in exposed coastal areas | Rooftop isolators sit in direct weather for the system's entire life |
| Lockable in the off position | Lockout/tagout requirement for safe isolation during maintenance |
Mounting the DC isolator somewhere that requires climbing onto the roof to operate it defeats much of its safety purpose — an isolator meant to let someone de-energize the array in an emergency should be reachable from the ground or a ladder without needing roof access.
Isolator selection isn't independent of cable sizing — both derive from the same underlying array voltage and current figures (Voc at minimum temperature, Isc × 1.25). Get the array's electrical characteristics right once, and both the cable and the isolator selection follow correctly.
Work through your array's Voc and Isc figures in the AS/NZS PV/Solar DC Cable Sizing calculator.