RCDs still in the spotlight
A new phase of our research is underway into the in-service performance and reliability of residual current devices (RCDs) in domestic premises.
The research, commissioned by the Electrical Safety Council, aims to:
- determine the adequacy of RCD main contacts under fault conditions
- explore the circuit conditions that could affect the operation of RCDs
- determine the influence of connected loads
- investigate whether equivalent technologies exist that can be relied upon without the need for periodic testing by users.
ERA Technology Ltd is conducting the research over a period of six months using a combination of desk-based study and laboratory tests. The results will be published on our website later this year.
The project builds on the initial research we commissioned ERA to undertake in 2007. This involved in-situ testing of RCDs in more than 600 domestic premises to gauge their reliability and to check that they still operated quickly enough to protect consumers from electrocution.
It was concluded from this initial research that, overall, RCDs in domestic installations are reasonably reliable in the long term, provided they have been selected and installed correctly, and that the integral test button is operated regularly.
However, of the RCDs tested in the 2007 research, almost 3% failed the timing test. This was largely attributed to ingress of moisture or contamination, component misalignment, or severe disruption of the main contact surfaces causing contact welding.
The research also confirmed that consumers do not operate the test button regularly, if at all, and that other factors, such as the condition and use of the electrical installation, may adversely affect the operation of RCDs.
There were also indications from the desk-based study that electromechanical and voltage-dependent RCDs may perform differently in service. It was therefore decided to continue with our investigations into RCD performance to further consider the factors mentioned above. We will also be working with manufacturers to encourage them to continue to improve the reliability of their RCDs and to design out the need for regular functional testing by users.
It is also hoped that this latest research will explain why RCD test instruments sometimes indicate that an RCD has not tripped within the maximum time limit when installation loads left connected, but indicate that it has when the loads are disconnected.
We hope finally to answer the question – Do connected loads affect the test readings or the operation of the RCD itself? This question often arises when installers return what they believe to be faulty RCDs to suppliers only to be told that, according to the manufacturer, the device is working correctly!
Steve Curtler, the Campaign Manager responsible for the research, said: “We are determined to further our knowledge of the performance and reliability of RCDs to help ensure we provide the best and most accurate advice to consumers whilst raising awareness of the benefits of RCDs and encouraging their wider use in the home. Also, the revised requirements for electrical installations introduced last year put significantly greater emphasis on the use of RCDs for additional protection against electric shock, so we need to ensure industry can support and provide the latest guidance to designers and installers on the correct selection and application of RCDs. In the meantime, we will be continuing with our campaign to promote the wider use of RCDs and to encourage consumers and landlords to use the test button regularly to check that they are still functioning.”
We would like to thank the ECA, BEAMA, Schneider Electric Limited and Greenbrook Electrical for their support to this study through participation in our RCD Research Steering Committee.
If you would like to support this project by sharing your RCD experiences with us, please email us at rcds@esc.org.uk or write to:
RCD Project, Electrical Safety Council, 18 Buckingham Gate, London, SW1E 6LB.
