Mitigating Non-Tripping of RCDs

Non-tripping of an RCD may be due to a fault within the RCD or due to external factors, and can have serious consequences if not detected. A non-functioning RCD leaves the user without the expected protection from shock and fire risk.

A faulty RCD may be blinded and therefore cannot recognise the fault. In other cases, the RCD may well see the fault but cannot trip because the trip mechanism is stuck or because the electronic circuity is faulty and there is some critical defect in the RCD that prevents it from tripping.

While contact welding is a rare occurrence nowadays it nonetheless can occur in exceptional cases. Failure of the activation means within an RCD may result in non tripping under a residual current fault condition. To ensure that the RCD contacts are able to open under a fault condition, WA has developed a range of Auto Reclosing RCDs (ARDs) which includes Self Testing. These RCDs carry out self testing every 2 – 3 seconds without opening the contacts. However, they can be configured to automatically open the contacts on a specific self test at intervals of three to six months. In this case the RCD contacts will open momentarily, e.g. for about 30mS, and reclose automatically once the self test has confirmed that the contacts opened correctly.

WA offers products with this unique feature to customers, and offers the technology for this feature to OEMs. This new generation Auto Reclosing RCD (ARD) is becoming more and more popular and is certainly set to become a significant part of the overall RCD industry in the coming years.

The benefits of the ARDs are enormous. The technology allows us to test the complete RCD from input right through to output with the contacts open. While the contacts may only remain open for about 30 milliseconds, it is long enough to detect the open state but also short enough to ensure no major disruption in terms of power loss.