What is an RCD and does my house need one?
Short answer
An RCD (Residual Current Device) is a safety device that cuts power within milliseconds if it detects current leaking to earth — the typical cause of fatal electric shocks. Modern NZ wiring rules require RCD protection on circuits feeding socket outlets and many other locations. Older NZ houses without RCDs are legal but materially less safe; most insurance-related electrical work upgrades to RCDs now standard.
Source: AS/NZS 3000 Wiring Rules. Updated May 2026.
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Check a builderKey facts
- RCD trips on leakage to earth (the main shock pathway)
- Required on new wiring for sockets per AS/NZS 3000 wiring rules
- Older houses with no RCD aren't illegal but are less safe
- Typical retrofit cost: $200-500 per circuit at the switchboard
- RCBO combines RCD + MCB into one device — common in modern boards
RCD vs circuit breaker (MCB)
Circuit breaker (MCB) protects the wiring from overload — trips on too much current.
RCD protects you from shock — trips on small current leaking through your body to earth.
Most modern boards combine the two with RCBOs (RCD + MCB in one). The result: every circuit has both overload AND leakage protection.
When to retrofit
If your switchboard still has porcelain fuses or no RCD/RCBO devices, retrofitting is among the highest-ROI safety upgrades you can do. Costs $1,500-3,500 for a switchboard replacement.
Anyone with kids in the house, anyone living near saltwater (corrosion accelerates leakage), and anyone in an older home should prioritise this.
Knowing the rules is half the job. The other half is knowing who you're hiring. Check any NZ builder against the public record: company status, licensing and insolvency notices, from the official NZ sources.
Related questions
Sources: AS/NZS 3000 Wiring Rules; Electrical (Safety) Regulations 2010. General information for NZ homeowners, not legal advice. Building rules change and vary by council, so confirm critical details on the official source before acting. Last updated 2026-05.