Could an unfused R.C.D. protected spur, from a complient ring final circuit, supplying a single outdoor socket via 1.5mm2 6242Y cable of max. length 300mm through a brick wall from an indoor socket outlet be considered compliant?
Actual MCBs that aren't antique tend to operate on high currents in well less than a half-cycle, as has been suggested here already: they are "current limiting", so they can force the current to a zero before its natural zero-crossing. But the wiring regulations give the curves going down to 100 ms (not 10 ms). Presumably that's because it's all that can be guaranteed for an MCB according to the expected product standard. In my ~20 year old copy of IEC60898 I see no requirement to be quicker than 100 ms for any fault current; no requirement on let-through either, except that a specification of it should be available to the product's user. So if you go only by what the standard requires, the let-through could be absurdly high. It's necessary to use the manufacturer's let-through specification to avoid depending on the 100 ms assumption, but I don't see what the regs can improve if the product standards don't specify more.
Actual MCBs that aren't antique tend to operate on high currents in well less than a half-cycle, as has been suggested here already: they are "current limiting", so they can force the current to a zero before its natural zero-crossing. But the wiring regulations give the curves going down to 100 ms (not 10 ms). Presumably that's because it's all that can be guaranteed for an MCB according to the expected product standard. In my ~20 year old copy of IEC60898 I see no requirement to be quicker than 100 ms for any fault current; no requirement on let-through either, except that a specification of it should be available to the product's user. So if you go only by what the standard requires, the let-through could be absurdly high. It's necessary to use the manufacturer's let-through specification to avoid depending on the 100 ms assumption, but I don't see what the regs can improve if the product standards don't specify more.
