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AS/NZS 3000-2018
RCD Fundamentals — Why Solar AC Circuits Need Them
A Residual Current Device (RCD) monitors the difference between the current flowing out on the active conductor and returning on the neutral conductor. If this difference exceeds the trip threshold (typically 30 mA for personnel protection), the RCD trips within 300 ms — fast enough to prevent electrocution. The Wiring Rules (AS/NZS 3000-2018) mandate RCD protection for solar AC circuits as they are installed in domestic and commercial premises and personnel may work on them.
Which Type of RCD for Solar?
RCD Type | Detects | Solar Application |
|---|---|---|
Type AC | Sinusoidal AC leakage only | Not suitable — solar inverters produce DC components that can blind Type AC RCDs |
Type A | AC leakage + pulsating DC up to 6 mA | Minimum required for solar AC circuits per AS 3000-2018 |
Type F | Type A + composite frequency AC (for VFD applications) | Use where inverter produces high-frequency AC components |
Type B | AC + pulsating DC + smooth DC | Required where inverter produces significant DC leakage — some three-phase inverters |
Critical Rule: Never use a standard Type AC RCD on a solar AC circuit. A grid-interactive inverter that injects even 6 mA of DC into the neutral conductor will saturate a Type AC RCD's toroid, rendering it unable to detect AC earth leakage — precisely the fault it is meant to protect against. Always use Type A minimum.
RCD Placement for Solar
An RCD (or RCBO — RCD with overcurrent protection combined) must protect the solar AC circuit from the switchboard
The RCD must be on the supply side of the solar connection point — it protects the wiring and any person who might contact the inverter's AC terminals
Where the solar AC circuit is long (more than 30 m), a second RCD at the inverter end may be warranted to limit the protected zone
For hybrid systems with battery inverter-chargers, the charger AC input must also be RCD-protected
Engr. Jason Morales — Founder, SolarEnergyPH
