Question 1

What is the difference between Type AC, A, F, and B RCDs?

Accepted Answer

Type AC trips on AC residual currents only. Type A adds pulsating DC residual currents (e.g. from rectified loads with capacitors); this is the New Zealand minimum. Type F adds composite waveforms typical of variable frequency drives. Type B adds smooth DC residual currents (above 10 mA), which is required for many EV chargers and grid-connected solar inverters where the DC side can develop a true earth fault.

Question 2

Does AS/NZS 3000 require RCDs on every circuit?

Accepted Answer

AS/NZS 3000:2018 mandates 30 mA RCD protection on socket outlet circuits, lighting circuits, and circuits supplying handheld and portable equipment in residential, commercial, and industrial installations. Fixed appliance circuits (water heaters, heating) generally do not require an RCD unless they supply a wet area or specific exempt installation. The calculator highlights which circuits need 30 mA RCDs based on the load type.

Question 3

When do I need a Type B RCD?

Accepted Answer

Type B is required when the load can produce smooth DC residual current that would saturate or mask a Type A or F RCD. The most common cases are EV chargers without internal Type B detection (Mode 3 chargers above 16 A typically include Type B internally; smaller ones may not), grid-connected inverters with non-isolated topology, and some VFD installations. Confirm with the manufacturer datasheet; if a Type B is needed and you fit a Type A, the RCD may not detect a real DC fault.

Question 4

Why has New Zealand mandated Type A RCDs?

Accepted Answer

New Zealand AS/NZS 3000 amendments require Type A as the minimum because modern domestic loads (LED drivers, switchmode supplies, induction cooktops) produce pulsating DC residual currents that a Type AC cannot reliably detect. Type AC RCDs in New Zealand new installations are no longer compliant for socket outlet protection. Australia has not mandated this nationally yet, but Type A is recommended for all new work and is required for solar PV and EV charger circuits.

Question 5

Are RCDs and RCBOs the same thing?

Accepted Answer

No. An RCD detects residual (earth-leakage) current only and trips when leakage exceeds the rated sensitivity (e.g. 30 mA). An RCBO is an RCD combined with a miniature circuit breaker in a single device, providing both residual current protection and overload or short-circuit protection. RCBOs are generally preferred over a separate RCD plus MCB because they isolate only the affected circuit on a fault rather than tripping the whole switchboard subsection.

RCD Selection Calculator

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RCD Selection for AS/NZS 3000:2018

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