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.
perspicacious: The design then evolved a bit to allow the slightly smaller metric cable 2.5mm and to permit use of 32 amp MCBs rather than 30 amp fuses. It is all bit empirical, but has a good record in practice.
But, it has been deemed that there is now a new qualifier in 433.1.204 regarding load distribution in the cable..........
Regards
BOD
"...under the intended conditions of use, the load current in any part of the circuit is unlikely to exceed for long periods the current carrying capacity (Iz) of the cable."
I suppose that the overloading could occur in say a commercial kitchen in a restaurant or pub.
Even the 1981 15th edition regs. recognized ring overloading, and probably previous editions as well. Appendix 5 required a ring final circuit to cover not more than 100 m2 in area in household installations, . Consideration was to be made of kitchens where a separate circuit may be required.
If used as a length of fuse wire, 2.5mm2 copper wire would be rated at approx. 80 Amps.
Talking about fuse wire, 433.1.204 still allows a ring final circuit to be protected by a B.S. 3036 length of fuse wire rated at 30 Amps. That shows confidence in the time tested ring final circuit's design.
perspicacious: The design then evolved a bit to allow the slightly smaller metric cable 2.5mm and to permit use of 32 amp MCBs rather than 30 amp fuses. It is all bit empirical, but has a good record in practice.
But, it has been deemed that there is now a new qualifier in 433.1.204 regarding load distribution in the cable..........
Regards
BOD
"...under the intended conditions of use, the load current in any part of the circuit is unlikely to exceed for long periods the current carrying capacity (Iz) of the cable."
I suppose that the overloading could occur in say a commercial kitchen in a restaurant or pub.
Even the 1981 15th edition regs. recognized ring overloading, and probably previous editions as well. Appendix 5 required a ring final circuit to cover not more than 100 m2 in area in household installations, . Consideration was to be made of kitchens where a separate circuit may be required.
If used as a length of fuse wire, 2.5mm2 copper wire would be rated at approx. 80 Amps.
Talking about fuse wire, 433.1.204 still allows a ring final circuit to be protected by a B.S. 3036 length of fuse wire rated at 30 Amps. That shows confidence in the time tested ring final circuit's design.
