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.

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

AS/NZS 3000 requires RCD protection on final subcircuits in the locations where people are most exposed to shock. In a domestic installation that broadly means socket-outlet circuits and lighting circuits, and the rules have steadily widened the scope across editions 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.

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 give you the clause and the verbatim text for the exact scenario, 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 only smooth sinusoidal AC residual current. It is the oldest type and is increasingly inadequate for modern installations.
• 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.

The trend across the industry is clear: Type A is becoming the practical default for general circuits, and Type AC is being designed out. 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 requires RCDs to be tested as part of the verification of an installation, and there are two distinct tests, which are often confused.

The push-button test only confirms the mechanical trip mechanism operates. It tells you the device can switch off — it does not tell you it switches off fast enough, or at the right current. The push-button test is a maintenance check, not a compliance test.

The instrument test is the one that proves compliance. Using an RCD tester, you verify the device trips within the required time at its rated residual current, and that it does not trip below a defined lower current. This trip-time and trip-current test is what demonstrates the RCD will actually protect a person, and it is what belongs in your verification records.

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.
• Quoting an alteration to an older board without allowing for the RCD upgrade the alteration triggers.
• Relying on the push-button test alone and never instrument-testing trip time and trip current.

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.