Any electricians - light keeps blowing fuse

One of our downstairs lights has been consistently blowing the fuse when switched on after 1-5 minutes. No problem with any of the other lights.

All seems wired up ok at switch and ceiling rose, have tried different light and switch. Anything else to look at before i call in an electrician?

all you can do is check the connections are all ok - a bad earth with show up as scorching or blackened wires.

After 1.5mins...

Take a close look at the fuse wire John and see if it's 'Blown' (short) or parted in the middle with a blob on each loose end (overload). If your circuitry is made up of up and downstairs circiuts then simply remove all lamps from your downstairs circiut and re-make the fuse wire, if it holds then you know your cabling and terminations are fine, replace lamps one at a time to diagnose if it's the total load your putting on the circuit or an internal fault on a lamp (lamps are actually fused on the filament supports but not knowing what your running then the above advice is the most simplistic way to diagnose where the fault is).

you need to check if there is a fault to earth by testing the phase and neutral wires for insulation resistance...at the switch on the phase and switch wire.(usually has a red marker to indicate switch wire)..then at the rose ....then at the light fitting.you need to seperate and label the wires to pevent mix up and test when the power is turned off.this will determine where the fault is occurring.ie betwixt rose and switch or rose and light fitting.this cuts down on the guessing work ...pity ya not local im on holiday with nowt to do but surf the net all day.
ps how many lights do you have fitted on that circuit?

There are a number of lights on the downstairs circuit - around 7. No problem with most of the lights, only issue with one. The light with which there is a problem is in a small extension. With the light off the others can be on (or off) without issue. Switch the light on and the fuse blows within a couple of minutes, regardless of the other lights being on or off. No charring at either switch or rose but the fuse on the consumer unit shows some charring (pretty old unit though). The fuse wire itself seems to have almost melted.

Tried a new celing rose and switch. Still the same problem.

GK, have tested the resistance of the cable from switch to ceiling rose, seems quite low (under an ohm), is this in spec?

Not sure what more I can do, think an electrician should be next before I end up looking like Beaker from the muppets.

check if the resistance between the wire(phase,neutral and earth at all the points between the fuse board and the light...the resistance should be very high.if it helps use the setting for audio buzz for continuity...if it buzzes when you check between the colours then you have a fault.if resistance is very low between the red and blue or red and earth then you have poorinsulation somewhere ...maybe a mouse in theattic has chewed thru at some point..

hang on ....u said wire?....how old is the fuse board...perhaps you are drawing too much current and just blowing the fuse..is anything else apart from lights on that circuit...a suggestion may be to turn all the other lights off except for the suspect 1and see if it still blows.i strongly suggest you replace the fuse board as well....rcd split board will be just fine...100 amp rating..

gibbleking":1y8zgj8t said:

check if the resistance between the wire(phase,neutral and earth at all the points between the fuse board and the light...the resistance should be very high.if it helps use the setting for audio buzz for continuity...if it buzzes when you check between the colours then you have a fault.if resistance is very low between the red and blue or red and earth then you have poorinsulation somewhere ...maybe a mouse in theattic has chewed thru at some point..

Click to expand...

Ah-ha, understood. Bloody mice.

gibbleking":xfbqyr27 said:

hang on ....u said wire?....how old is the fuse board...perhaps you are drawing too much current and just blowing the fuse..is anything else apart from lights on that circuit...a suggestion may be to turn all the other lights off except for the suspect 1and see if it still blows.i strongly suggest you replace the fuse board as well....rcd split board will be just fine...100 amp rating..

Click to expand...

Probably 30 years old, same as the house.

Lights only circuit. Last change was about 5 years ago. Fuse blew once in that time, I think due to a duff halogen bulb. Replaced wylex fuse with one of these



Replacing the fuse board is waaaay outta my league.

pity....ive done at least 250 so far....going to cost ya about 80 quid for the board and another 90 or so for labour..if ya can get some one....us sparkies are worse than plumbers ...this is what i would charge for non family members....for family i charge a nice roast dinner and choccie bars..