BS 7671 Section 521.8.3

Starting  a new “circuit” at a protective device makes no sense. 

It's useful to have a word to distinguish points that are grouped together but somehow separate from other points - e.g. “the upstairs lighting circuit” or the “cooker circuit” or the “socket circuit” - usually the only difference is that they are connected to a different way in a DB or CU. If the protective device they're connected to isn't to be the distinguishing feature, then what would be?

I'd add that many if not all the characteristics of a “circuit” - required live conductor size, c.p.c. size, size of load it can supply, v.d., maximum cable length, disconnection time relate to the characteristics of the protective device - and so can differ quite substantially from those connected to a different protective device.

My only gripe is that the definition is limited to overcurrent protective devices - I'd probably prefer to include all protective devices - e.g. RCDs as well.

    - Andy.

Starting  a new “circuit” at a protective device makes no sense. 

It's useful to have a word to distinguish points that are grouped together but somehow separate from other points - e.g. “the upstairs lighting circuit” or the “cooker circuit” or the “socket circuit” - usually the only difference is that they are connected to a different way in a DB or CU. If the protective device they're connected to isn't to be the distinguishing feature, then what would be?

I'd add that many if not all the characteristics of a “circuit” - required live conductor size, c.p.c. size, size of load it can supply, v.d., maximum cable length, disconnection time relate to the characteristics of the protective device - and so can differ quite substantially from those connected to a different protective device.

My only gripe is that the definition is limited to overcurrent protective devices - I'd probably prefer to include all protective devices - e.g. RCDs as well.

    - Andy.