light switch keeps tripping RCD

[diyplumber1980]

hi all, was hoping to get some advice from the experts!

Last week my double 4ft tube lights went in the kitchen. So i changed the tubes and the starter motors for both tubes, and the light worked fine for 2 days. Then one tube stopped working. OK, not a problem, 1 tube is enough.

But then today when i was in the kitchen, turned the light on and after about a minute i heard a "crackling" sound from the light, and then the light went out (and tripped the downstairs lighting RCD on the fuse box) I could smell a really strong smell of burning, similar to burning rubber, coming from near the light fitting.

I then touched the tube holder which was very very hot! i decided to remove the starter motors from the light to stay on the safe side. Switched the RCD back on from the fuse box. Downstairs lights worked fine, but then i went in the kithcen and accidently switched the light on (out of habit) and it tripped the RCD for downstairs lighting, cutting the power. I switched the RCD back on and then pressed the light switch and again, it tripped the RCD, and does it every time i switch the light on.

I also noticed than when i took the started motor out, it said "single, 220-240v, 80/125w". However on the old Starter motors, it said "4-65w". Could this have been the reason the tubes went so quick?

Also why does the power keep tripping everytime i switch on the kitchen light? have the wires burnt out somewhere?

 

[ban-all-sheds]

Seems likely that there's damaged wiring somewhere.

They aren't motors, BTW.

 

[Lectrician]

Sounds like its time for a new fitting.

 

[diyplumber1980]

thanks for the reply lads. I've taken the cover off the light fitting and taken some pics. You can see one part, im guessing the transformer, looks slightly burnt, as the other similar part looks fine. I this simply a case of a new fitting?

Is their any way i can check this is the case before actually going out, getting a new fitting and still having the problem?

heres some pics

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• diyplumber1980
• 26 Jul 2013
• 1

here you can see this part is slightly yellowish, and it you look around the top of it, you can see burn marks

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• diyplumber1980
• 26 Jul 2013
• 1

this is pic of the mains cable, it looks fine, no burn marks etc so i'm guessing the mains lighting cables are ok??

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• diyplumber1980
• 26 Jul 2013
• 1

this pic is further out, and shows the difference in colour in the transformer to the other transformer.

 

[bernardgreen]

They are chokes, not transformers. The yellow one almost certain has serioulsy overheated and is no longer servicable.

A choke determines the amount of current that can flow through the tube.

Most common cause of over heating is an internal short circuit in the choke creating a shorted turn which gets very hot.

 

[securespark]

If you are proficient, disconnect the "faulty" choke and see if the tripping ceases.

At least then you can have one tube until you can change the fitting or choke.

 

[diyplumber1980]

If you are proficient, disconnect the "faulty" choke and see if the tripping ceases.

At least then you can have one tube until you can change the fitting or choke.

thanks for the replies lads.

I've disconnected the faulty choke and simply capped off the two cables that were coming out of it, using insulating tape. When i try the light switches, it no longer cuts of the power so thats one thing sorted!

however I've then tried fitting one tube to the other side, with the choke thats ok but it does not work. i've got the correct voltage starter, but still not working.

Does anyone know what could be wrong? do the two wires from the other choke need to be connected together?

 

[bernardgreen]

When a choke overheats it is due to excessive current passing through it after it became faulty and unable to control that current.

This excessive current flows through the heaters at each end of the tube until the starter operates. It is possible that the heaters of the tube conneced to the faulty choke have been burnt out by the excessive current.

 

[diyplumber1980]

thanks for the reply. Looks like i'm going to need a new light fitting!

 

[plugwash]

It's possible that both chokes have failed but one has failed more dramatically than the other. It's also possible there is a fault with some other component or maybe there is some sort of protective device hidden somewhere in the fitting. I've also seen flourescent fittings with the two tubes in series but I think your fitting is a bit big to be one of those.

Pretty much all the components in a flouresent fitting can be replaced but it would likely only be worth doing so for a fancy fitting or for a setup where you have a number of fittings which you want to match.