Wylex Fusebox - Wired Fuses vs MCB

[vonsworld]

Hello

I have an old Wylex Fusebox which has some re-wireable fuses and some MCB upgrades.

I know there is no great advantage in upgrading rewireable fuses to MCB's other than they can be reset quickly. They do not offer RCD protection.

However can you tell me, do MCB's react quicker to a fault than a wired fuse?

Thanks
Robin

 

[SUNRAY]

Hello

I have an old Wylex Fusebox which has some re-wireable fuses and some MCB upgrades.

I know there is no great advantage in upgrading rewireable fuses to MCB's other than they can be reset quickly. They do not offer RCD protection.

However can you tell me, do MCB's react quicker to a fault than a wired fuse?

Thanks
Robin

The short answer is; Maybe.
The longer answer is; Generally yes they are quicker.

 

[ericmark]

The MCB is a duel device, the thermal part is slow, and the magnetic part very fast, but it needs 5 times the current of the thermal part.

The graphs of the fuse and MCB's cross, but although the cartridge fuse is reasonable predictable, the rewireable fuse varies so not quite as cut and dried.

The problem with the MCB is if the current is just slightly below trip point, it will not trip on the magnetic part, so the loop impedance and volt drop are critical. Where with the fuse it just takes a slight bit longer.

So before replacing a fuse with a MCB the loop impedance must be measured.