RCD Selection Calculator

Parameters

Seven inputs drive the recommendation. This is what each one means, what it is measured in, and exactly which part of the output it controls.

Circuit type (eight options)

Lighting, socket outlet, fixed appliance, motor, EV charger, hot water, pool or spa, and medical. This is the primary input: it drives both the sensitivity and the device type.

How it is used. Medical always returns Type B. Pool or spa returns 30 mA. Socket outlet returns 30 mA, or 10 mA in a wet area or bathroom. Indoor lighting returns 100 mA. Everything else returns 30 mA.

Phase type (single phase or three phase)

Single phase returns a 2-pole device covering active and neutral. Three phase returns a 4-pole device covering three actives and neutral.

Gotcha. Pole count is all this input controls. It does not change the sensitivity, the type, or the disconnection time, and there is no option for a 3-pole device on a three-wire circuit with no neutral.

Circuit rated current (amperes)

The rated current of the circuit the RCD sits in, normally the rating of the protective device in front of it.

Typical range. 10 to 63 A for final subcircuits, higher for submains. The field accepts 1 to 200 A.

Gotcha. The calculator rounds up to the next standard RCD frame size from 16, 20, 25, 32, 40, 50, 63, 80, 100, and 125 A. Anything under 16 A therefore returns a 16 A device, and anything above 125 A returns 125 A. Above 63 A the result carries a warning to check the device short-circuit rating.

Location (indoor dry, outdoor, wet area, bathroom)

The environment the circuit serves. It sharpens the sensitivity and sets the maximum disconnection time reported with the result.

How it is used. Bathroom and wet area report 100 milliseconds, outdoor reports 200 milliseconds, indoor reports 300 milliseconds. A wet area or bathroom combined with a socket outlet or hot water circuit drops the sensitivity from 30 mA to 10 mA. Outdoor also flags that portable RCD protection should be considered for maintenance work.

Country (Australia or New Zealand)

Selecting New Zealand on a socket outlet circuit forces the recommendation up to Type A, reflecting the New Zealand requirement that Type AC is no longer acceptable for socket outlet protection.

Gotcha. The country setting has no effect on any circuit type other than socket outlets, and it does not change sensitivity or disconnection time.

Variable speed drive (checkbox)

Tick this when the load includes a variable speed drive, frequency converter, or soft starter, which can produce residual current that is not a clean sine wave.

How it is used. On a motor circuit it returns Type F, or Type B when non-linear loads is also ticked. On an EV charger circuit it returns Type A. On any other circuit type it returns Type F.

Non-linear loads (checkbox)

Tick this for harmonic-heavy loads such as large rectifier fronts, banks of switch-mode supplies, or drives without input filtering.

Gotcha. On its own this box upgrades motor and EV charger circuits to Type B on its own, without needing the variable speed drive box. On every other circuit type it only adds a note about monitoring harmonic distortion. It changes the device type only when it is combined with the variable speed drive box on a motor circuit, where it lifts the recommendation from Type F to Type B.

Assumptions and limits

What the tool assumes

• The recommendation is a decision tree over those seven inputs. It is not a clause-by-clause application of AS/NZS 3000 Section 2.6, and the engine itself carries a draft status note that appears with every result.
• The disconnection times of 100, 200, and 300 milliseconds are values the tool assigns by location. AS/NZS 3000 and AS/NZS 61008 set RCD performance by device rating and residual current, not by whether the room is wet, so treat those figures as a design target rather than a quoted requirement.
• Sensitivity is chosen from location and circuit type only. There is no calculation of standing earth leakage from connected equipment, which is the usual cause of nuisance tripping on circuits with many electronic loads.

Known quirks you will see in the output

• An indoor lighting circuit returns 100 mA. For Australian domestic work, Clause 2.6.3.2.2 requires 30 mA on final subcircuits including lighting, so take 30 mA as the default and treat the 100 mA result as out of step with current practice.
• Ordinary Australian socket outlet and lighting circuits return Type AC. Current practice, and the New Zealand requirement, is Type A as the minimum for new work. Read a Type AC result as the floor, not the recommendation.
• On a New Zealand socket outlet circuit the headline recommendation correctly moves up to Type A, but the check named RCD type adequate for load still tests the type from before that upgrade and reports a failure. Read it as confirmation that the Type A requirement was applied, not as a defect in the recommendation.
• The suggested products are generic manufacturer names attached to the type and sensitivity. They are not a product selection and they are not checked for availability or rating.

What this calculator does not do

• No discrimination check between a 30 mA final RCD and a 100 or 300 mA upstream device, and no time-delayed or selective type S option.
• No short-circuit rating or backup protection check on the RCD itself, and no choice between a separate RCD plus circuit breaker and a combined RCBO.
• No coverage of the special-location rules that override the general ones: medical body-protected and cardiac-protected areas to AS/NZS 3003, construction and demolition sites to AS/NZS 3012, swimming pool and spa zones, marinas, or caravan parks.
• No assessment of solar photovoltaic or battery systems, where the inverter topology decides whether Type B is mandatory.

Use the result as a starting point for the conversation, then check it against the current edition of AS/NZS 3000, against the load manufacturer installation instructions, particularly for EV chargers and inverters, and against the local supply authority or jurisdiction rules. Have the selection signed off by the person responsible for the installation. Nothing on this page has been validated or certified by a chartered professional engineer.

Worked examples

Three complete runs through the decision tree, including the checks the calculator reports.

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

In Australian domestic and residential installations, Clause 2.6.3.2.2 requires 30 mA RCD protection on all final subcircuits, including fixed-wired appliances such as hot water systems and air conditioners. The only exceptions are extra-low voltage subcircuits, separated supply subcircuits, and repairs. In non-domestic installations, Clause 2.6.3.2.3.3 requires 30 mA RCDs on final subcircuits rated up to 32 A supplying socket outlets, lighting, directly connected hand-held equipment, and directly connected equipment that presents an increased risk of electric shock. 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.