You are reading a single comment by @fizzy.bleach and its replies.
Click here to read the full conversation.
-
The MCB value is determined by the cable capacity, 'Cable Is King'. When it's installed the routing and cable type are noted, real world values for capacity checked and a value arrived at which will indicate that the breaker will operate before the cable overheats and catches fire.
It's a big part of electrical installation and a paragraph on a forum wouldn't do it justice but that's the essence of it.
Other considerations would be diversity, how many light bulbs has the circuit been designed for? In your case they may have used a larger cable/mcb capacity and a single circuit as it saves some of the issues with upstairs/downstairs shared neutrals etc.
Airhead
@fizzy.bleach
speaking of electrics, my whole house (3 bed 1930s semi) has one lighting circuit for the whole place – upstairs, downstairs, extension (but not outside lights) on a B10 MCB. Is that MCB OK for a lighting circuit, which i thought should be 6A?