Total light failure following repair of bulb holders.

[chainsaw_masochist]

Spent some time this afternoon replacing three of defective light fittings for my elderly aunt in her basement flat. These are the rose type of bulb-holder that are screwed into the ceiling. Everything seemed fine after completing each of these repairs individually, then checked that all of these worked together, fine also. So packed up and headed off home to be called 10 minutes into journey and informed of a total light failure for the whole flat. Went straight back to investigate and as aunt described no damn lights. Checked the lighting fuse breaker on the consumer unit to see that the small pushbutton was ‘out’. This is quite an old CU perhaps thirty or forty years old. Pushed it back in and noticed a small flash and the button popped out again which it continues to do.

I should add that the defective lights have been like this for some while, probably two or three years (don’t ask – she seems content with the situation ). Also all of the lighting is low energy so I can’t see how the circuit could be overloaded.

Any idea what the problem might be?

 

[RF Lighting]

Sounds like you've created a short circuit somewhere

 

[chainsaw_masochist]

Thanks for the quick reply, RF. But why would the circuit work perfectly well immediately following the replaced holders and then go t1ts-up subsequently?

 

[viewer]

If it worked OK then failed after a little use, suspect that there is a strand of wire which has not gone through the connector and was able release its tension and move when the bulb got hot. Once it had moved to create a short it would stay that way.

 

[chainsaw_masochist]

That makes sense, viewer. Based on your prognosis, then, my intention would be to disconnect the replaced holders, then reconnect them individually leaving them on for half-hour or so each. Then give the whole lot the current. Sound plausible?

 

[JohnD]

or it could be that you have the old "connect all the blacks together" mistake that causes a short-circuit when the switch is used.

take all the bulbs out as well just in case one of them blew shorted.

 

[viewer]

If they did work then it can't be a wrong wiring situation - the short would have been 'wired in'. The only way to find out what is wrong is to unscrew the rose pendants and have a look. The other problem, less likely, is that a screw holding the new rose has penetrated two wires and there was originally just a poor short giving a hot spot (hope that makes sense). As the spot got hotter the insulation would burn back to leave a direct metal to metal contact. Sorry, no easy answer - you just have to look at everything. Best of luck.

 

[JohnD]

with the "all blacks together" error, the lamp is on with the switch in the "off" position but the short circuit occurs when you switch it "on"

is a surprise if you have a pull-switch

but it is a good idea to open up all the roses and inspect them

 

[viewer]

Sorry JohnD my bad.

 

[JohnD]

 

[chainsaw_masochist]

Problem resolved, chaps. Viewer hit the nail on the head with the "screw penetrating two wires" hunch. Having removed the offending bulb-holder, about six inches in there is an old nail poking down from the floor above. It’s strategically placed so as the holder is fixed to the ceiling it has managed to pierce the cores. There must have remained a smidgin of plastic to allow the light to work properly for fifteen minutes or so and then the blow as it has melted.

Yes, John, I have done the “all blacks together” in the dim and distant past but not this time.

All’s well now, so thanks again.