RCD safety switches explained: why every Australian home needs them

How RCDs work

In a healthy circuit, the current flowing in the active wire equals the current returning through the neutral wire. If there's an imbalance — as little as 30 milliamps — it means electricity is escaping somewhere (possibly through a person). The RCD detects this and trips instantly.

Legal requirements

• 01Under AS/NZS 3000, all new residential circuits — power AND lighting — must be RCD protected.
• 02NSW regulations require RCD protection for all new installations and significant renovations.
• 03In commercial and industrial settings, RCD protection is mandatory on all socket-outlet circuits up to 32A and on lighting circuits in specific environments (construction sites, wet areas).
• 04Current best practice is individual RCBOs (combined RCD plus circuit breaker) per circuit, so a fault on one circuit doesn't shut down the entire property.

Test every 3 to 6 months

WA's Director of Energy Safety states: 'The widespread installation of RCDs has markedly reduced the incidence of electric shocks, but it is vital to test them to ensure the switches work when they are needed most.'

• 01How to test: press the Test or T button on each RCD. The switch should immediately flick to OFF. Then reset it.
• 02If the switch doesn't trip: the mechanical components may have seized. The RCD may not protect you in a real fault and needs urgent replacement.
• 03Annual professional testing: a licensed electrician should verify trip time (≤300ms for Type I, ≤40ms for Type II) using specialised test equipment during your annual electrical safety inspection.

Common mistake

Many homeowners confuse RCDs with circuit breakers. Circuit breakers protect the circuit from overload and short circuit. RCDs protect people from electric shock. You need both.