RCD Selection Calculator
Select the right RCD type and sensitivity, including NZ Type A mandate, per AS/NZS 3000:2018.
Inputs
Results
Recommended RCD Type
AC
30 mA
2P RCD @ 20 A
Sensitivity adequate for location
30 mA (<= 100)
RCD type adequate for load
1 (>= 1)
Disconnection time
300 ms (<= 300)
RCD rating ≥ circuit current
20 A (<= 20)
Recommended Products (Informational)
AC-type 30mA RCD (e.g., Clipsal, Schneider Electric, Legrand, Eaton)
DRAFT: Pending CPEng review for compliance accuracy
RCD Selection for AS/NZS 3000:2018
A residual current device (RCD) continuously compares the current flowing out on the active with the current returning on the neutral. Under healthy conditions the two are equal; when some current leaks to earth, through a person, a damaged cable, or a wet appliance, the balance is lost and the RCD disconnects within milliseconds. The standard sensitivity for personal protection is 30 mA, fast enough to prevent ventricular fibrillation in most circumstances.
When AS/NZS 3000 requires an RCD
AS/NZS 3000:2018 requires 30 mA RCD protection on socket outlet circuits, lighting circuits, and circuits supplying handheld or portable equipment across residential, commercial, and industrial installations. Fixed-wired appliances such as hot water systems and air conditioners generally do not need an RCD unless they serve a wet area or fall under a specific clause. Special locations, bathrooms, swimming pools, construction sites, and medical areas, carry additional requirements that override the general rules.
The four RCD types
The right type depends on the kind of residual current a load can produce. Modern electronics rectify the mains, so the leakage is no longer a clean sine wave, and a basic Type AC can be blinded by it.
- Type AC: detects AC sinusoidal residual current only. No longer the minimum for socket outlets in New Zealand.
- Type A: AC plus pulsating DC residual current from rectified loads (LED drivers, switchmode supplies, induction cooktops). The New Zealand minimum and the recommended default for new Australian work.
- Type F: Type A behaviour plus the composite frequencies produced by single-phase variable frequency drives, common on pool pumps and some HVAC.
- Type B: all of the above plus smooth DC residual current above 6 mA. Required where a load can develop a true DC earth fault, principally EV chargers and grid-connected solar.
Common scenarios
- Kitchen and bathroom socket outlets: 30 mA Type A.
- EV charger (Mode 3): Type B, unless the charger has integrated DC fault detection and the manufacturer permits a Type A upstream.
- Grid-connected solar inverter: Type B on the AC side for non-isolated (transformerless) inverters.
- Pool pump on a VFD: Type F (or Type B if a smooth DC component is possible).
- General lighting and power: 30 mA Type A on each final subcircuit; an RCBO isolates only the faulted circuit.
Common questions
What is the difference between Type AC, A, F, and B RCDs?+
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.
Does AS/NZS 3000 require RCDs on every circuit?+
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.
When do I need a Type B RCD?+
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.
Why has New Zealand mandated Type A RCDs?+
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.
Are RCDs and RCBOs the same thing?+
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.
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