With reference to 433.1.204 and cable as installed has min capacity of 20A if protected by a 30A or 32A. If the protective device is reduced to 20A how is the new minimum as installed capacity calculated or arrived at ? I've been looking in the Electrical Installation Design Guide, but the answer is avoiding my eyes.
In principle I believe that one could wire a ring final circuit in 1.5mm cable protected by a 20 amp MCB. It is not a standard circuit, but that does not mean prohibited. A 20 amp ring final in 1.5mm should be no less safe than the common arrangement of a 30/32 amp ring final in 2.5mm.
But back in the real world, why on earth would anyone want such an odd circuit ? A standard 20 amp radial circuit would almost certainly be cheaper and simpler.
BTW, I have installed ELV lighting circuits as a ring in 1.5mm on a 10 amp fuse. To reduce voltage drop. A 2.5mm radial was rejected because a pair of 2.5mm conductors wont fit most light switches.
In principle I believe that one could wire a ring final circuit in 1.5mm cable protected by a 20 amp MCB. It is not a standard circuit, but that does not mean prohibited. A 20 amp ring final in 1.5mm should be no less safe than the common arrangement of a 30/32 amp ring final in 2.5mm.
But back in the real world, why on earth would anyone want such an odd circuit ? A standard 20 amp radial circuit would almost certainly be cheaper and simpler.
BTW, I have installed ELV lighting circuits as a ring in 1.5mm on a 10 amp fuse. To reduce voltage drop. A 2.5mm radial was rejected because a pair of 2.5mm conductors wont fit most light switches.
