If you’ve been testing RCDs (Residual Current Devices) you’ve likely seen labels like Type AC or Type A — maybe even Type B or F. These labels refer to the types of fault currents the RCD can detect, and getting it wrong could mean an RCD fails to trip when tested.
Here’s a quick but practical look at the differences — and what you actually need to consider when testing.
RCD Types Explained
Different RCD types are designed to detect different waveforms of leakage current:
Type AC: Detects pure sinusoidal AC leakage only. These are the original, basic RCDs — fine for traditional resistive loads (heaters, kettles, etc.).
Type A: Detects both AC and pulsating DC leakage. That includes fault currents from appliances with switch-mode power supplies — common in modern appliances.
Type F: Designed to detect leakage from high-frequency or variable-speed equipment (like modern appliances with motor drives or inverter technology).
Type B: Detects AC, pulsating DC, and smooth DC leakage. Beneficial for equipment like EV chargers, solar inverters, VFDs, and similar equipment. These are typically used in industrial or specialised applications.
Current Australian wiring rules (AS/NZS 3000) require Type A RCDs for all new general-purpose circuits — including residential, commercial, and workplace environments. That’s because the majority of newer appliances can generate pulsating DC leakage, which a Type AC simply won’t detect.
However, for existing installations, there is no mandatory upgrade requirement — a legacy Type AC RCD remains compliant for the purposes of in-service safety inspection and testing under AS/NZS 3760.
Do you need a tester with that capability?
Not necessarily (yet). AS/NZS 3760 does not currently require testing with waveform-specific fault currents — just the standard trip time test at the rated current of the RCD. So if you're using a typical appliance tester for portable RCDs, or even a installation tester for fixed devices, you're not expected to simulate a Type A fault current. That said, some advanced appliance testers, such as the Metrel Alpha EE, now include selectable fault current waveforms for different RCD types.
