Consumer unit question and main fuse

[who took my fluke?]

The consumer unit i have bought for a house has a 100a main breaker, yet the main supplier fuse is only 80A. Surely this is not right, yet i have been told that this is ok. i have always bought 80A breakers instead. what do you think?

 

[Adam_151]

It does not matter that the incommer has a switching capacity in excess of the upstream overcurrent device, no reason at all to swap the incommer for one with a lower switching capacity

 

[HDRW]

The consumer unit i have bought for a house has a 100a main breaker, yet the main supplier fuse is only 80A. Surely this is not right, yet i have been told that this is ok. i have always bought 80A breakers instead. what do you think?

The "main breaker" is only a switch, so overrating it is not a problem. If it was an actual Circuit Breaker (that is something that disconnects the supply when there is excess current) then it would be a different matter, but the thing you have (often called an incomer) will only break the circuit when you operate the lever by hand.

The same applies to RCDs, by the way - they don't break on overcurrent, only on a current imbalance (a leak from Phase to Earth for example). RCD incomers are marked with a current rating like 63 or 80A, but this is their carrying capacity, not the current at which they will trip. This often surprises people new to modern mains practices - it certainly did me when I found out!

Cheers,

Howard