I have a 30A breaker on an old style fuse board dedicated to the electric shower. I want to upgrade this to 45A. Will i need to buy a new 45A breaker or will it just be a case of replacing the 30A fuse wire inside the breaker with 45A wire?
You either have old-fashioned rewirable fuses, or you have miniature circuit breakers - MCB's. There's no such thing (or shouldn't be) as a breaker with fuse wire inside. (Though there are fuseholders with cartridge fuses inside).
Either way, a rewirable fuse should not be rewired with higher amperage wire than it is rated for. A MCB can only be replaced. On top of that the holder a rewirable fuse plugs into is sized for a particular rating of rewirable fuse - or for the same rating of replacement MCB.
The rated fuse (or trip) value should only be increased if the rating of the fixed wiring is appropriate - I'd be concerned somone asking questions about the "fuse wire inside the breaker" isn't someone that should really be messing with this.
(a) There is no fuse wire inside a "breaker". Do you have rewireable fuses, cartridge fuses, or MCBs?
(b) A 30A fuse carrier may only be rated at 30A and be unsuitable for use at 45A
(c) Cartridge fuses are different sizes for different ratings and you would need to replace both the carrier and the base unit.
(d) If it's an old board you might find it difficult to get compatible bits.
(e) You MUST NOT upgrade the fuse/MCB rating without ensuring that the cable remains adequately protected. You MUST to de-rate the cable if you are using a rewireable fuse, if the cable runs through insulation, etc. If you are going from 30A to 45A you almost certainly need to run new cable.
(f) AIUI this is Notifiable Work under Part P of the Building Regulations and you need a building regs application to the local council.
(g) You may have to bring other parts of the installation, particularly earthing and supplementary bonding, up to current standards.
Owain
think you need to figure out which youve got first, fuse wire, breaker, or catrridge fuse.
NT
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