RCD Research
RCD - Reliability Investigation
The remit of the Electrical Safety Council includes campaigning in specific areas of perceived electrical safety risk to consumers. One of the Council's first campaigns is a review of the in-service reliability of residual current devices (RCDs) used for supplementary protection against electric shock (ie having a rated operating
current =30 mA).
Although it is generally accepted that such use of RCDs reduces the risk of injury in particular circumstances, there are some lingering doubts as to the long term in-service reliability of the devices.
The Council is therefore commissioning independent research into the in-service reliability of residual current devices (RCDs) used in homes to provide supplementary protection against electric shock.
The research is being carried out in two phases, the first of which has now been completed. The objectives of the first phase, carried out by ERA Technology Ltd, were to:
- determine, through a study of available literature, the mechanisms by which RCDs fail to operate correctly after prolonged periods of inactivity in domestic environments
- provide an opinion on the relevance of these mechanisms for the RCDs currently on sale in the UK
- provide recommendations for an RCD test programme to be conducted in the second phase of the research.
A report detailing the findings of the first, desk-based, phase of the research can be viewed here.
In brief, the findings of the research were that:
- Previous research published in Italy indicated that electromechanical RCDs had an average failure rate of 7.1%. However, if the RCDs were operated regularly by means of the integral test button, this figure fell to 2.8%, indicating that RCD reliability improved if they had been operated regularly
- from the available evidence, the primary mode of failure on electromechanical RCDs was ingress of fine particles of dust and moisture causing the moving components to stick or to operate more slowly than intended
- whilst manufacturers of electronic RCDs claimed that their products were more reliable than electromechanical RCDs, very little evidence to support this was found. Previous research in the USA suggests that the reliability of electronic RCDs may be similar to that of electromechanical RCDs.
The second stage of the research has recently commenced which will also be carried out by ERA, and has the following objectives:
- To determine the likely effect, if any, to the results of testing RCDs in domestic premises with downstream loads connected
- To carry out the in situ testing of a range of 30mA RCDs installed in domestic premises. Any RCDs that fail to satisfy the tests prescribed in IET Guidance Note 3 will be replaced with new and the failed units will be examined in detail in order to ascertain the cause of the mal-operation
- To determine an overall reliability rate of RCDs by analysing the results obtained from examination of the failed RCDs.
- To ensure that the results of the field testing are statistically valid, tests will be conducted on a relatively large number of RCDs in premises where their age and operating history is known and, ideally, where there are significant numbers of devices of the same type and age. It is therefore intended to concentrate the research on particular types of premises such as student halls of residence, housing association properties and local authority housing estates.
We are pleased to report that a number of organisations have agreed to help in this research and we are very grateful for their support and assistance in allowing the testing to be carried out in their properties. In particular we would like to thank:
Lewisham Borough Council
Newham Homes
Orbit Housing
SOHA Housing
The Council would welcome feedback from electrical contractors, users and others about their experience of the in-service reliability of RCDs in the field, including RCBOs, SRCDs and PRCDs.
In particular, those regularly undertaking periodic inspections of electrical installations may have invaluable experience of testing installed RCDs that would be of interest.
If you would also like to share your experience with us, please send details to rcds@electricalsafetycouncil.org.uk
or, alternatively, write to:
RCD Project
Electrical Safety Council
18 Buckingham Gate
London
SW1E 6LB
All the findings will be published on completion of the research. If, as the Council hopes, the research confirms that there are no inherent reliability problems with RCDs, the Council will begin to more actively promote their widespread use in the home.
