STRANGE WALL LIGHTS!

[RONCHAM]

Hi all -

I have 2 wall lights and each has 2 bulbs – they both operate from a single wall switch. The wiring concealed behind the lights is in very poor condition and insulation has dropped off in places. Recently I slightly disturbed one light whilst decorating - there was a small flash and the mcb was tripped. I have now removed that light - there were thin insulated wires going off to each bulb (in poor condition) and these were crudely joined to the incoming cable with insulating tape. The incoming cable emerging from the wall is just a red, black and earth wire - the red wire is live regardless whether the switch is on/off. Obviously the 2 wall lights are interconnected but I now also find the other wall light remains on all the time regardless whether the switch is on or off? I have not disturbed the other wall light or examined the wall switch but can do so if necessary.

I will be grateful if anyone can explain this and suggest how the failed wall light was wired to the incoming cable and the other wall light?? (A diagram would be most helpful!).

Regards.

 

[footprints]

I am no sparks, but I suggest the contacts on the switch are fused together.

 

[JohnD]

I suggest that you replace all the perished wiring.

Until that is done, buy yourself a few metres of heat-shrink sleeving, and a hot air gun. You can push it over the wires, and, when heated, it shrinks to grip tightly. Use the same colours as the old cores to avoid later confusion.

If it is not very old, the insulation may have been overheated. This used to be common with old filament, and especialy halogen, bulbs, but is very unlikely with modern LEDs

Very likely your lighting fittings also need replacement, and possibly the switches too.

If you have old rubber-insulated cables, the whole house needs rewiring.

"insulating tape" is absolutely unacceptable.

 

[RONCHAM]

Thanks for the replies. Yes, it could well be the switch.

The wall light wiring threads through hollow metal tubes to each bulb so I think the outer sheath of suitable wire would have to be removed as there's tight twists and turns to negotiate - presumably the insulation to individual wires would be safe?

Switches and house wiring are relatively modern and not rubber insulated - it's only the short arrangement in the shallow space behind the light fitting which is crude and in poor condition. It's a wonder there hasn't been a problem before with wires touching - it was just the minor disturbance that did it.

 

[JohnD]

you can probably reach the ends that have been disturbed. It probably cracked when moved.

I think the conduits ought to be earthed but you may have thin slip-tube and I don't know the correct thing to do.

 

[ericmark]

The use of conduit (tube) was common with older homes, pre-1966 lights did not need to be earthed, and even when twin and earth was used, often the earth was not connected, and it could be wired in singles, not twin and earth, there is also mineral insulated, unusual in houses, normally only used with stone building or high fire risk buildings, seems unlikely you have this cable, to be frank even as an electrician I would get some one use to working with it to do any work, it depends on a good seal at ends, and not a DIY job.

There were some batches of poor cable, the plasticiser would leach out, often as a green gue, and the cables became brittle, specially with a little heat, Australia had a problem not so long ago with Chinese imported cable, supplied by Woolworths, and Woolworths had to pay out for homes to be rewired as a result.

Most plastic cable lasts for years, at least 50 years, but there have been bad batches, the fitting of RCD's has highlighted many wiring problems, and it seems likely you will need a rewire, I would say you need an EICR (electrical installation condition report) but the problem is disturbing the wires to do the report could make it worse.

Pictures are good, then people are not guessing.

 

[RONCHAM]

Thanks for the further replies above.
To be honest, because of the poor state of things, I've taken photos but they're probably less revealing than my written explanation (not sure if I should've inserted photos as thumbnails or full images?). The cable emerging from the wall is sheathed and comprises insulated red, black and earth wires - these all seem sound. The hollow metal tube going off to each bulb is S-shaped and I doubt any sheathed flex/cable would thread through so I'm thinking the outer sheath would need to be removed and 2 individual (insulated) wires used if this is deemed safe to do? - it's presumably what was originally done.

 

[JohnD]

The cores appear to be PVC insulated so I think the degradation will be due to heat from the lamp. Use sleeving on the exposed parts. Use LEDs in future, which run cooler.

I think that if you remove the lamp you will find very little degradation behind, but you should sleeve it.

It's possible that scraps of old wire were used when fitting the lamps, especially if they were second-hand or re-used.

Old conduit often had cables threaded in during assembly, it is much harder to do once the conduit is plastered into the wall. It's possible to poke or pull cable into straight old conduit, but any bends or joints make it harder. There ought to be an accessible round box at changes of direction.

When rewiring, you can often get new cable into short runs of conduit to light switches, which saves the effort of replastering.

 

[RONCHAM]

Thanks for that.
I'm not sure if the cable in the wall is in conduit but my main concern is the wiring from the ends of this cable through the wall light to the bulbs. I doubt the wall lights were secondhand and they probably came wired up to each bulb. Because there's only a shallow recess to cover the wires some bodger obviously decided to join up the wires and wrap in insulating tape. Possibly small connector blocks would be better and safer, or heat shrink?

 

[RONCHAM]

I have another pair of wall lights on the opposite wall – these and the offending ones use a 2-gang wall switch. When I switched the wires around the (remaining) wall light on the offending wall switched on and off ok. Which suggests (as footprints said) the dodgy wiring at the wall light fused the contacts on the wall switch. That remaining wall light has equally suspect wiring and needs sorting.

As an aside, do they make wall switches where the wires are held by spring clamps (like Wagos) rather than extremely fiddly micro screws?