Old MCCBs & MCACBs Data

Under 13th and 14th Editions of the Wiring Regulations, the requirements were not to achieve loop impedance low enough to achieve a specific disconnection time, but to permit a fault current (for faults to earth) to flow of at least a multiple of what we now call the nominal current rating, I_n of the protective device (if memory serves, 3 times for fuses, 1.5 times for circuit-breakers).

So, the old Regs don't include these time-current curves. They first appeared in 15th Ed (1981) and the circuit-breakers by that time were BS 3871.

Unless any older heads can advise otherwise, I think therefore that the only place you might find a time-current characteristic is if the manufacturer issued one, they appeared in a technical book of the time, or they just happen to be from a standard that has one (BS 3871 I think came along in 1965, but it depends on the classification to that standard also).

Under 13th and 14th Editions of the Wiring Regulations, the requirements were not to achieve loop impedance low enough to achieve a specific disconnection time, but to permit a fault current (for faults to earth) to flow of at least a multiple of what we now call the nominal current rating, I_n of the protective device (if memory serves, 3 times for fuses, 1.5 times for circuit-breakers).

So, the old Regs don't include these time-current curves. They first appeared in 15th Ed (1981) and the circuit-breakers by that time were BS 3871.

Unless any older heads can advise otherwise, I think therefore that the only place you might find a time-current characteristic is if the manufacturer issued one, they appeared in a technical book of the time, or they just happen to be from a standard that has one (BS 3871 I think came along in 1965, but it depends on the classification to that standard also).