RCD requirements under AS/NZS 3000

Why 30 mA matters

The number that does the work is 30 milliamps. An RCD used for personal protection is required to disconnect when the leakage current reaches 30 mA or below. That figure is chosen because it sits below the level of current that causes the heart to fibrillate for the typical shock duration: it is the threshold between a frightening shock and a fatal one.

This is why AS/NZS 3000 distinguishes between RCDs used for "additional protection" of people and devices used purely to protect equipment or installations, which may operate at higher currents. When the Wiring Rules call for RCD protection of socket-outlets and lighting in the places people live and work, they mean a device rated at 30 mA or less. Clause 2.6.1 recognises fixed-setting RCDs rated at no more than 30 mA as additional protection, and every requirement in Clause 2.6.3 calls for a maximum rated residual current of 30 mA.

It is worth being precise with clients here. A circuit breaker protects the wiring from overload and short circuit. It does not protect a person from electric shock. Only an RCD does that. The two are not interchangeable, and a board with breakers but no RCDs is not providing personal protection.

Where AS/NZS 3000 requires RCD protection

In Australia, AS/NZS 3000:2018 Clause 2.6.3.2.2 requires RCDs with a maximum rated residual current of 30 mA on all final subcircuits in domestic and residential installations, fitted at the switchboard where the final subcircuit starts. For commercial and industrial installations, Clause 2.6.3.2.3.3 requires them on final subcircuits rated up to 32 A that supply socket-outlets, lighting, directly connected hand-held equipment, and equipment with an increased risk of electric shock. The scope has widened with each edition of the standard.

The practical complication is existing installations. When you add to or alter an existing circuit (a new GPO into a bathroom, an extra light, a circuit extension) you can trigger a requirement to bring that circuit up to current RCD standards even though the rest of the board predates the rule. A circuit that was compliant when it was installed may not stay compliant once you touch it. Clause 2.6.3.2.5(a) makes socket-outlets added to an existing circuit meet the RCD requirements for a new subcircuit, with protection needed from the start of the additional wiring; extensions to lighting-only circuits are an exception. Clause 2.6.3.2.5(b) requires RCDs on every final subcircuit when all the circuit protection on a switchboard is replaced, and like-for-like repairs are covered by Clause 2.6.3.2.6.

This is one of the most common places electricians get caught: quoting a small addition without allowing for the RCD upgrade the addition forces. Before you price an alteration on an older installation, confirm what the current edition of AS/NZS 3000 requires for the circuit you are extending. StandardsMate™ will name the clause for the exact scenario and explain what it requires, including whether the existing-installation provisions apply.

RCD types: AC, A and B

Not all RCDs detect all kinds of fault current. The type matters, and choosing the wrong one means the device may not trip on a real fault.

• Type AC detects sinusoidal AC residual current. AS/NZS 3000:2018 still describes it as the general type used in Australia, but it can miss the fault currents modern electronic loads produce.
• Type A detects sinusoidal AC and pulsating DC residual current. Most circuits feeding modern electronic loads (appliances with switch-mode power supplies, LED drivers, variable-speed equipment) should be on Type A.
• Type B detects AC, pulsating DC and smooth DC residual current, and is used where equipment can produce smooth DC fault current, such as some EV chargers and inverter equipment.

Clause 2.6.2.2 lists the RCD types (it also covers Type F) and requires devices that comply with AS/NZS 3190, AS/NZS 61008.1, AS/NZS 61009.1 or IEC 62423. Across the industry, Type A is becoming the practical default for general circuits. That is industry practice rather than a Wiring Rules requirement: modern electronic loads can produce fault currents a Type AC device simply will not see, leaving the circuit unprotected against exactly the faults that occur in practice. When in doubt, confirm the type required for the load you are protecting rather than fitting whatever is in the van.

Testing and verifying an RCD

An RCD that is fitted but faulty is a false sense of safety. AS/NZS 3000:2018 Clause 8.3.3.1(f) makes operation of RCDs one of the mandatory tests, and Clause 8.3.10 requires every RCD to be tested, then the isolation of all switched poles checked after it trips. There are two ways to do the test, and they are often confused.

The push-button test uses the device's own integral test button. Clause 8.3.10 accepts it as verification of the RCD's function, and a note to that clause says there is no requirement to test the operating time. It confirms the device can switch off. It does not tell you how fast it switches off, or at what current.

The instrument test uses an RCD tester to trip the device at its rated residual current and measure how long it takes. Clause 8.3.10 accepts it too, and it tells you far more: a slow or sticking device shows up here and not on the button. Many electricians instrument test every RCD and record the trip times, and some network operators and regulators expect it, so check what applies where you work.

Advise clients that RCDs should also be push-button tested periodically through the life of the installation: the mechanism can seize. Many electricians leave a sticker on the board with the test date and a reminder.

Common RCD mistakes on site

A few errors come up again and again, and all of them are avoidable:

• Treating a circuit breaker as personal protection: it is not, and only an RCD protects against shock.
• Fitting a Type AC device on a circuit with significant electronic load, leaving it blind to realistic fault currents.
• Sharing one RCD across too many circuits, so a single nuisance trip takes out half the installation and the client starts bypassing it. Clause 2.6.2.4(b) allows no more than three final subcircuits per RCD in a residential installation, with at least two RCDs where there is more than one final subcircuit.
• Quoting an alteration to an older board without allowing for the RCD upgrade the alteration triggers.
• Relying on the push-button test alone, so a device that trips slowly is never found.

None of these are complicated to avoid: they come down to knowing the current requirement for the specific job. That is exactly the kind of question to settle before you quote, not after the inspector raises it.