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You are forgetting that those breakers also have a thermal protection and therefore at 40A consumption on a 20A breaker type C will also trip after 25 seconds

The thermal characteristics of the C/B with a moderate overload, rather than a drastic short circuit, could certainly make all the difference. While thinking of this, keep in mind also my comments above about some appliances in the U.K. having 0.5 sq mm. cords as well.

As David has pointed out, there is nothing to stop us using type-C breakers in residential applications, so long as the appropriate disconnect times can be achieved. Back when I was a kid in the early 1970s, my father rewired a 1930's house using the Crabtree C50 range C/Bs (I'll leave it your imagination to work out just how he happened to be using commercial-spec breakers! [Linked Image]).

That was on an old urban TN-S supply with a solid ground path on the armor of the cable, and thus a very low loop impedance. (It was also before the 5 sec. & 0.4 sec. disconnect times were part of the Regs., but I'm sure it would have satisfied those requirements anyway.)

I wouldn't mind betting that at the time, it was probably the only house in the street to have any sort of breakers rather than the rewireable fuses which were the most common form of protection in the early 70s.



[This message has been edited by pauluk (edited 10-20-2002).]