when the bulb blows, so does a fuse..............why?

[sarah beeny's lovechild]

In my kitchen I have a 4 lamp halogen spotlight fitting, each bulb being 50w. When ever one of the bulbs blow, so does the 5A fuse in the consumer board, which is for the whole house lighting circuit.

Why does this happen, and what can I do to fix it?

Thanks

 

[ban-all-sheds]

Very unusual for a fuse to blow - fuses are sometimes used as a solution to MCB trips in these circumstances..

You must be running very close to the limit already, if not over it.

Try splitting the lighting circuit into two - 1 upstairs, one downstairs, but watch out for borrowed neutrals with the landing light.

 

[kendor]

prospective short circuit current and the like!

 

[sarah beeny's lovechild]

ban-all-sheds

thanks for your reply. I never have all the lights on when the fuse blows, but it may make sense. I only have one 5A fused lighting circuit, which runs 10 pendant lights (most are energy efficient or 40W normal bulbs) a 4x50W halogen fitting in the kitchen, and a 3x50W fitting in the bathroom.

Am i right in that i should only be running 1kW (10 x 100 W lights on a circuit)

If so, how easy is it for an electrician to split a circuit. ( I have a spare couple of slots on my consumer board)

Thanks

 

[kendor]

the original post asked why the fuse blows when a lamp's filament blows, it doesn't matter if there is only one lamp on the 5A circuit it can blow due to the high currents involved when there is a temporary short circuit as often happens when a lamp blows

 

[ban-all-sheds]

5A gives you 1150W to play with, but as you say you're unlikely to have all of them on at once.

Not too hard to split them, provided access under the floors upstairs is OK. Do you know the routes the cables take? Is the run from upstairs floor to the loft visible/accessible, e.g. through a cupboard/wardrobe?

Could a new cable from the fusebox to the loft be installed without too much grief?

 

[sarah beeny's lovechild]

not sure i could get a cable into the loft easily.

looks like i'll have to grin and bear it, and change a fuse once a year when it goes pop!!

thanks

 

[mapj1]

Is it actually blowing a hot wire fuse - not firing a trip? Firing trips is common and the advice may be to change the trip for a type with better surge handling (type C instead of type B) if one is available for that consumer unit, and the rest of the wiring is in good order. If it really is blowing a fuse however, it does sound a bit near the knuckle (or the lights are particularly poorly designed bulbs that internally arc on failure - some cheaper ones are renown for that)
It may be tha there are already more than one wiore coming to the fuse bboard for lights, as up and downstairs normally follow different routes. Only looking will tell you.

 

[ban-all-sheds]

the original post asked why the fuse blows when a lamp's filament blows, it doesn't matter if there is only one lamp on the 5A circuit it can blow due to the high currents involved when there is a temporary short circuit as often happens when a lamp blows

A great deal of anecdotal evidence says that such transients frequently trip Type 1 or Type B MCBs, but fuses are virtually immune.

I did briefly wonder if there might be something wrong with the circuit - the presence of fuses probably means no RCD, so a high-ish impedance fault could load the circuit higher than would be expected, but it's pretty unlikely, even more so to be a fault that persisted for a long time without worsening...

 

[securespark]

the original post asked why the fuse blows when a lamp's filament blows, it doesn't matter if there is only one lamp on the 5A circuit it can blow due to the high currents involved when there is a temporary short circuit as often happens when a lamp blows

Yes! If these Halogen lamps are mains voltage, why not try lamps with Ballotini fuses in them?

You should be using fused lamps especially if you have a dimmer attached, as unfused lamp failure can very easily toast the dimmer.....