"keith" wrote
| I'm going to reuse a circuitbreaker position that used to
| power the bell transformer, to provide a dedicated fused
| connection unit for a new alarm system. The circuit
| breaker is 6A, and I'd use a 3A fuse in the FCU, so in
| theory I can use 1mm lighting cable.
| But something is nagging me that I ought to use cable
| at least enough for a 13A socket, in case some future
| house owner swops the fuses for 13A?

Even if someone swaps the fuse in the FCU for 13A, the circuit is still
protected by a 6A MCB. If someone upgrades the MCB then they should take
responsibility for ensuring the circuit is suitable.

That said, if you use 2.5mm you are probably okay for up to a 20A radial
circuit.

Owain