Published: 10 March 2014
Category: Q&A
Frank asks this question, which concerns two concealed ring main circuits having a1.0mm circuit protective conductor (CPC) that cannot easily be re-wired, and whether the existing circuit breaker could be replaced by an RCBO. It has been answered by the ECA (Regulations and Legislation):
This Q & A is one of thousands posted in our Technical Expertise area, and answered on a daily basis by our Voltimum Experts.
Question: I have just completed an electrical installation condition report (EICR) on an installation that has two ring main circuits wired in PVC/PVC insulated cable containing a 1.00mm CPC and protected by a 30A 'C' Type circuit breaker.
The installation is all concealed wiring and re-wiring is not an option at present, because of the hardwood floors and high quality decoration.?
The cables are in good condition, although obviously old, and the standard of the installation is very good. Insulation resistance tests at 500V produced results all >200MΩ and L/E loop tests of 0.88 and 0.91. The PFC measured at the terminals of the circuit breakers was 2.46kA.
Would it be permissible to recommend replacing the circuit breakers with a 32A 30mA Type B RCBO to provide fault and additional protection (although BS 7671: 2008 states that the combination of a 1.00mm CPC / 32A breaker is not permitted)?
Answer: If the existing condition of the installation is very good, as you say, then there is no need to do anything as the original installation was installed to an earlier edition of BS 7671.
You can, however, make a recommendation as per your suggestion as an improvement to the existing installation.
To see many more Q & A in Voltimum UK's Experts Area, please click on the link. Experts from leading organisations provide online answers to your technical questions on a broad range of subjects. Our searchable database of existing Q & As now contains over 3,500 entries; you can browse through them here.