RCD selection calculator
Check if an RCD is required and test the trip time.
Reads Electricity (Safety) Regulations 2010 and AS/NZS 3000:2018. Tables checked 27 Sept 2026.
Try a job 8
Each job fills in example values. Replace them with your values.
- Choose the RCD for an EV chargerThe RCD a 32 A home EV charger circuit needs in NZ.
- Check the RCD for house lightingThe RCD a lighting circuit needs in Australia.
- Check the RCD for a classroomThe RCD rule for socket‑outlets in a school.
- Check the RCD for a child-care centreThe 10 mA rule where young children are.
- Check a measured RCD trip timeWhether 28 ms at rated current and 12 ms at five times pass.
- Choose the RCD for a patient areaThe residual current and times for a patient-protection RCD.
- Choose the RCD for a fixed machineWhether a fixed appliance in a workshop needs an RCD.
- Choose the RCD for a vending machineThe RCD rule for a ride or a vending machine.
Inputs
A worked example with the default inputs.
- Country
- New Zealand
- Installation
- Residential
- Final subcircuit
- Socket‑outlets
- Circuit rating
- 20 A
- Socket-outlet rating
- 10 A
- Protection duty
- Protection against electric shock
- Rated residual current
- 30 mA
- Check measured trip times
- No
Additional RCD protection
Required, 30 mA
- Rated residual current the clause requires
- 30mA
- Maximum rated residual current for the duty
- 30mA
- Limit at the rated residual current
- 300ms
- Limit at five times rated
- 40ms
- Maximum disconnection time
- 0.4s
This result is a design aid. Verify it against the current standard.
Calculation steps
- Additional protection requiredYes
AS/NZS 3000:2018 Cl 2.6.3.3.1
- Rated residual current the clause requires30mA
AS/NZS 3000:2018 Cl 2.6.3.3.1
- Maximum rated residual current for the duty30mA
Electricity (Safety) Regulations 2010 reg 24
- Trip limit at the rated residual current300ms
Electricity (Safety) Regulations 2010 reg 24
- Trip limit at five times the rated residual current40ms
Electricity (Safety) Regulations 2010 reg 24
- Maximum disconnection time0.4s
AS/NZS 3000:2018 Cl 5.7.2
- Must not trip at or below15mA
Electricity (Safety) Regulations 2010 reg 24
About this calculator
How this is calculated
The tool says whether a circuit needs additional RCD protection. It picks the rated residual current. It can also test a measured trip time against the limits.
- Need. The tool reads the installation and the circuit type. It decides whether Clause 2.6.3.3.1 of AS/NZS 3000:2018 asks for additional protection.
- Rated current. It gives the rated residual current that the clause requires for that circuit.
- Maximum for the duty. In New Zealand you pick the duty: shock, property, patient or children. The tool gives the highest rated residual current for that duty (Electricity (Safety) Regulations 2010 reg 24).
- Trip limits. It gives the trip limit at the rated residual current. It also gives the limit at five times that current (reg 24).
- Disconnection time. It gives the maximum disconnection time (Cl 5.7.2).
- Measured result. If you enter two trip times, the tool compares them with the limits. It also gives the current below which the device must not trip.
| Step | Table or clause | What it decides |
|---|---|---|
| Need for protection | Cl 2.6.3.3.1 | Whether the circuit needs an RCD |
| Rated current and trip limits | Reg 24 | The rating and the trip times by duty |
| Disconnection time | Cl 5.7.2 | The longest time to clear |
Worked example
- Socket‑outlets in a home, tested at 250 ms and 50 ms. The tool requires 30 mA protection. The limits are 300 ms at the rated current and 40 ms at five times it. The 50 ms reading exceeds 40 ms, so the test fails.
Limits
- The tool does not choose a make or model. It does not check discrimination between RCDs.
- It does not test nuisance tripping from earth leakage. A circuit with high leakage needs a site test.
- The type of RCD (A, F or B) comes from the equipment on the circuit. See the learn page on RCD types.
- The tool reads AS/NZS 3000:2018. Check the regulations for later changes.
- Australia caps the circuit and New Zealand caps the socket‑outlet in some cases. Check the hint on the form.
See also: RCD types and where they are required, Testing to Section 8 and Wet area zones.
Questions
The result is a design aid. Verify against the current standard.
What does the RCD selection tool do?
The tool reports whether the clauses it checks call for an RCD as additional protection on a final subcircuit. It gives the maximum rated residual current for the duty and the maximum trip times. It also checks measured trip times at the rated current and at five times that current against those limits.
Which clause and regulation does it use?
New Zealand circuits read AS/NZS 3000:2018 Clause 2.6.3.3, and Australian ones Clause 2.6.3.2.2 or Clause 2.6.3.2.3.3. A New Zealand electric vehicle circuit reads Clause 7.9.3 when domestic, and Clause 7.9.4 otherwise. A domestic Mode 2 circuit also takes the 30 mA of Clause 2.6.3.3.1. Trip limits come from Electricity (Safety) Regulations 2010 reg 24, and disconnection times from Clause 5.7.2.
What are the RCD trip time limits in New Zealand?
A shock protection RCD up to 30 mA has a 300 ms limit at its own rated residual current. At five times that current, its limit is 40 ms. Property protection takes an RCD rated up to 300 mA, with limits of 0.5 s and 0.15 s.
Why does a 40 amp circuit show no requirement?
In Australia, the tool reads Clause 2.6.3.2.3.3 outside a residential installation. That clause covers a final subcircuit rated 32 A or less, so above that the tool reports none. Clause 2.6.3.2.2 covers every final subcircuit of an Australian residential installation, at any rating. The New Zealand residential clause has no rating cap either.
Does the tool cover medical and patient areas?
Only in part. It reports regulation 24's 10 mA patient limits. It does not apply AS/NZS 3003, the patient areas standard. Read it for a medical location. The tool reads AS/NZS 3000 with Amendment 1. EV and Australian residential rows read the Amendment 1 to 3 compilation. Amendment 2 revised parts of Clause 2.6.3; check its current text.
Worked examples
- RCD tripping with no fault: add up the leakageAn RCD on a home office and kitchen trips with no fault found. Add up the standing leakage, check it against a third of 30 mA, and split it over two RCDs.
- Kitchen power points and the cooktop zonePlace power points and switches near a cooktop, an outdoor gas bottle and a gas vent. Check each distance to AS/NZS 3000 and hand the sink to the wet area tool.
- RCD arrangement for a house boardCheck a New Zealand house board of eight circuits on two RCDs. See what fails with a fourth circuit on one RCD or both lights on one, and the AU change.
- Wire a bathroom: zones, IP ratings and the RCDA New Zealand bathroom with a 1.6 m bath and an open shower, worked through the AS/NZS 3000 Section 6 zones, the IP each item needs, the RCD and bonding.
Background
- How many circuits can go on one RCDThe AS/NZS 3000 Cl 2.6.2.4 arrangement rules in plain words, which circuits need a 30 mA RCD in NZ and AU homes, how RCBOs count, and why the rules exist.
- Damp situations: the Section 6 zonesHow AS/NZS 3000 Section 6 zones the space around baths, showers, basins, spas, pools, fountains and saunas, how to read an IP code, and what A2 changed.
- RCD types and where they are requiredType AC, A, F and B, what each one detects, and the clauses that place them. The fault path behind them, worked on a 20 A circuit over 25 m.
Clauses and tables this tool reads
- AS/NZS 3000:2018 Cl 2.6.3.2.2Additional protection in Australia, domestic and residential
- AS/NZS 3000:2018 Cl 2.6.3.2.3.3Additional protection in Australia, non‑domestic
- AS/NZS 3000:2018 Cl 2.6.3.3.1Additional protection in New Zealand, residential
- AS/NZS 3000:2018 Cl 2.6.3.3.2Additional protection in New Zealand, non‑residential
- AS/NZS 3000:2018 Cl 5.7.2Disconnection times
- AS/NZS 3000:2018 Cl 7.9.1Scope of Clause 7.9, electric vehicle supplies
- AS/NZS 3000:2018 Cl 7.9.3.2Mode 2 electric vehicle charging, New Zealand
- AS/NZS 3000:2018 Cl 7.9.3.3Mode 3 and Mode 4 electric vehicle charging, New Zealand
Every clause and table, with how each was verified
Tables last checked on 27 Sept 2026.
Related tools
- EV charger circuit calculatorCheck EV chargers for spare capacity, cable size and RCD.AS/NZS 3000AS/NZS 3008.1.2AS/NZS 3008.1.1
- Cable size calculatorFind the smallest cable size that passes each check.AS/NZS 3008.1.2AS/NZS 3008.1.1AS/NZS 3000
- RCD arrangement checkCheck circuits per RCD and the lighting split.AS/NZS 3000
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