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ADAM HARDCASTLE: THIS WAS SPOTTED ON A RECENT JOB. WHERE DO YOU EVEN BEGIN WITH THE PROBLEMS? IT ALSO HAD AN EIGHT SOCKET RADIAL FED FROM ONE OF THE SOCKETS ON THE DOWNSTAIRS RING, WITH AN AIR-CONDITIONING UNIT COMING OFF ONE OF THESE RADIAL SOCKETS WIRED WITH 0.5 MM CABLE!
The object of periodic inspection and testing is to confirm the existing electrical installation is safe for continued use, based on the assumption that the installation was compliant with the requirements of edition of BS 7671 in use at that time.
The reported issue with a ring final circuit with an unfused spur supplying eight socket-outlets and an air-conditioning unit shows a disregard for the basic design considerations.
With the apparent age of the consumer unit, it is assumed that the additional eight socket-outlets were installed at a later date. Whoever undertook this work should have been aware of the requirements of ring final circuits. With regard to a 0.5 mm² cable supplying an AC unit, there could be no doubt that this cable is undersized and would result in overloading problems.
The use of a 40 A 100 mA RCD as a main switch would not offer any overload or additional protection for the electrical installation, although obviously installed before the current consideration of BS 7671 with regard to the potential current that could be drawn through the main switch from the rating A of the connected circuit-breakers of 74 A.
Where a non-compatible circuit-breaker has been installed, this can cause operational issues within the consumer unit.
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