Date   : Tue, 01 Sep 2009 09:51:40 +0100
From   : philb@... (Phil Blundell)
Subject: Leccy @ Acorn World '09

On Tue, 2009-09-01 at 01:44 +0200, Rick Murray wrote:
> Mmmm, is there such a thing as an RCD with a delay so it can cope with 
> brief surge currents?

I guess you mean an MCB, in which case the answer is yes (sort of).  

The prefix letter on an MCB - the B in B16, for example - represents the
level of instantaneous overload that the breaker will tolerate without
immediate tripping.  Type B are the fastest-tripping type (guaranteed to
trip at 300-500% rated current) and also the type that's usually fitted
as standard in the UK.  

Type C is somewhat slower tripping (guaranteed to trip at 500-1000%
rated current).  It might or might not be allowable to swap a type B for
type C depending on the other characteristics of the installation.

There are various other types as well for special purposes but they're
not the kind of thing you'd be likely to encounter in a domestic
installation.

p.