Serving Illawarra and Greater Sydney Test & Tag

RCD and PRCD explained

A residual current device (RCD) or a residual current circuit breaker (RCCB) commonly know as a safety switch is designed to isolate power when it detects an imbalance between the active and neutral conductor.


These imbalances are commonly caused by a current leakage through the earth. This leakage can be caused via a faulty appliance, wet conditions, insects, etc.

RCD/RCCB's are designed to disconnect power to the circuit when a difference is detected. This disconnection or tripping of these circuit breakers should happen within a legal time of 300ms (but less is better!). New circuit breakers trip between approximately 10 and 30ms

10mA RCDs may be used in areas of increased risk such as circuits supplying outdoor equipment, bathrooms, kindergartens and hospitals.

30mA trip sensitivity is the minimum requirement for providing personal protection. RCDs with lower trip sensitivity (i.e. 100mA or above), may be selected to avoid unwanted nuisance tripping when installing the RCD for equipment protection.

Testing (P)RCD's

RCD test Metrel MI3309BT

The purpose of this test is to ensure the proper operation of residual current devices (RCD) built into appliances/installations and portable residual current devices (PRCD). Trip-out time measurement verifies the sensitivity of a (P)RCD at selected residual currents.

PAT Delta MI 3309BT RCD screen

We test the (P)RCD two times, first time on the positive start polarity, a second time on the negative start polarity.

Positive and negative start polarity


Pin It