Lighting circuit fuse keeps going, what to try?

[Golaboots888]

Hello

I've got home from work and found the downstairs lights not working.
I replaced the fuse wire (yes I need a new consumer unit really) and it blew straight away, I don't think any of the lights were on, although there are two PIRs on the downstairs lighting circuit.

What should I be looking for? Keep replacing the fuse wire and checking the each light is actually off?

Thanks for any suggestions.

 

[Spark123]

No, replacing the fuse wire continuously is probably the worst thing you can do.
You can start by looking for things like outside light full of water, if you can isolate them then by all means do.
In order to locate the fault causing it to blow you need to use specialist test equipment so you may be better phoning an electrician.

 

[chivers67]

Are any unusual with transformers? If so make sure these are switched off.

Check all switches to see if any are loose or have signs of heat. Then check each ceiling rose.

Have tyou got a multimeter?

 

[sparkyspike]

To keep changing the fuse wire is not the best method really! Unless you have a meter, you can only really do visual checks. Have a look at the outside lights and see if there is any way that damp could have got in the lights or the sensors. Then have a hunt around for damaged cables (mice?) or dodgy looking light fittings.

If you do have a meter, you can split the circuit into two halves to eliminate parts of the circuit with the fault, until you eliminate the faulty part.

 

[ericmark]

I would remove all low energy bulbs and try them in a standard lamp. Seems they do sometimes go short circuit.

 

[Golaboots888]

Hello.

I'll isolate as much as I can and check the lights for visible damage.

I've got a multimeter and know how to use it. I'm dying to know how a 'specialist meter' could pinpoint the problem.

 

[Golaboots888]

To keep changing the fuse wire is not the best method really! Unless you have a meter, you can only really do visual checks. Have a look at the outside lights and see if there is any way that damp could have got in the lights or the sensors. Then have a hunt around for damaged cables (mice?) or dodgy looking light fittings.

If you do have a meter, you can split the circuit into two halves to eliminate parts of the circuit with the fault, until you eliminate the faulty part.

Splitting the circuit? Would this simply be breaking the 'ring main' in the ceiling roses (although 70% of the fittings are either downlighters or transformered fittings making it hard to get to.)

 

[Spark123]

I'm dying to know how a 'specialist meter' could pinpoint the problem.

An Insulation Resistance Tester and the knowledge of how to use it can be used to find out where a problem exists which isn't apparent using a multimeter which can only deliver a few mA.

 

[chivers67]

The circuit shouldn't be a ring but a radial loop in type. I'd start looking rather than spliting the circuit down you might end up giving yourself more work than you need and a headache as well, depending on your knowledge of course

 

[Golaboots888]

OK, outside lights all isolated. Energy saving bulbs all taken out. Switches all look physically ok but the fuse still goes.

Perhaps while the fuse it out I will do a continuity check on each switch to ensure that every light it off.

Then if it still happens atleast I can rule out all the transformers etc.

On a separate note are plug in MCB's available that retrofit into an old consumer unit? Are they a good idea? Much of a saving over getting the whole unit changed?

 

[ericmark]

You can try sniffing around in case a transformer has blown they often smell when they have blown.
It could be poor quality normal bulb. Good bulbs should have built in fuse because as they blow they can ionise and cause a short circuit that sometimes makes bulb go black as it blows so in the manufacture of the bulb they in UK included a fuse built in. However these are not always in the cheap imports.
And I have fitted the MCB's to my old Wylex boards and RCD's feeding them did it many years ago and been great.
In theory you should pay the council £115 for them to check you have done it correctly they call it PART P. I wrote to my MP but didn't do me much good still minimum charge of £115 which if I was doing £2000 worth of work may be fair. But to undo four screws and replace four fuse bases it seems daft.
Other option is to get a registered electrician to do the work.