Fuse v MCB

[bernardgreen]

The impossible happened..... The lamp on my workstation went out. A halogen capsule lamp had popped and gone plasmatic. This took out the power to the work station.

I removed the lamp from the lamp holder and went to the consumer unit to reset the MCB.

The B20 MCB had not tripped. but 3 amp fused supply to work station was blown, and the 3 amp fuse in the plug for the lamp was also blown.

I only mention this as some people believe that a fuse cannot possibly operate faster than an MCB and thus believe the use of FCU ( Fuses Connection Units) is a waste of money.

 

[sparkwright]

Sounds like discrimination worked like a treat, also demonstrates perhaps why someone we know doesn't like two identical fuses in line.

But as you said, this a rare occurrence so it's hardly an issue for you.

I wonder what would have happened if the work station was a 5amp. No difference I suppose.

 

[EFLImpudence]

As we don't know the current involved nor the csa of the cables and flex, it is difficult to know what the situation is.

What do you think would have happened without the 3A fuses?

 

[bernardgreen]

But as you said, this a rare occurrence so it's hardly an issue for you

Halogen capsules going plasmatic is not that rare, even a gentle tap can cause the filament to snap.

What do you think would have happened without the 3A fuses?

I would hope the MCD would have tripped and then the MCB could have been flicked back on. Changing fuses was a bit more time consuming

 

[sparkwright]

Halogen capsules going plasmatic is not that rare, even a gentle tap can cause the filament to snap.



I would hope the MCD would have tripped and then the MCB could have been flicked back on. Changing fuses was a bit more time consuming

Ah. You implied your light lamp going out was impossible, obviously tongue in cheek, perhaps you meant you were always working...

Assumed you'd rather the MCB DIDN'T go off, as this would perhaps cause other, more important things not to work, then again we don't know your wiring set up...

 

[bernardgreen]

as this would perhaps cause other, more important things not to work

only the work station and the socket for the Hi Fi would be affected if that MCB tripped.

 

[333rocky333]

i guess if the mcb was loaded up nearer 20 amp with other stuff then things may have been different

 

[JohnW2]

I only mention this as some people believe that a fuse cannot possibly operate faster than an MCB and thus believe the use of FCU ( Fuses Connection Units) is a waste of money.

Hmmm - I think that anyone who believes that any assertions can be made about such things probably "hasn't lived"!.

Over the years, in cases of multiple over-current devices in series (varying types and various ratings), I think I've probably seen most possible combinations of 'one device operating but another not'. That certainly includes fuses blowing before MCBs trips, and also higher-rated fuses or MCBs operating before lower-rated ones.

I think that anyone who lives in the real world has to accept that there is more than a little 'pot luck' involved in such matters!

Kind Regards, John

 

[SUNRAY]

While with BT a 60w bulb blowing and taking out a 30A BS88 sub main started an investigation.

The engineer couldn't get his head around a 5A wire fuse remaining intact, the fact that there was possibly hundreds of 40w fluo fittings on the submain but maybe only a dozen on each 5A fuse went right over his head.