Old Light Switch Wont Turn Off

[EdR]

A one way light switch in one of our bedrooms wont turn off.

I assumed it was a defective dimmer. So I changed it.

Initially it worked but about an hour later the trip at circuit board tripped, and when I turned it on again the light stayed on once again, regardless of switch.

Just out of interest I detached the switch all together and the switch stayed on.

There has been work in the loft - so I wonder whether a wire has been disturbed (technical term).

My thought is that there is a short somewhere between the switch and the ceiling rose. But how to find out where it is?

 

[Iggifer]

What kind of work are we talking about in the loft? Are we talking nails?

What kind of light fitting is it? Just a standard rose?

 

[OwainDIYer]

Open the ceiling rose and check for shorts between the live and switch live. If you don't have permanent live at the ceiling rose you must have a junction box somewhere go go up in the loft and look for it.

 

[EdR]

No - completely unrelated work - on the roof. But the person may have stood over (and therefore on) the wires going into the ceiling rose.

The ceiling rose appears standard to me - I did notice that the earth wires are not sleeved, and that the upstairs lighting wires all run under (rather than over) the insulation in the rafters.

 

[EdR]

No obvious signs of shorting. Everything appears secure etc. I have found the junction box.

 

[EdR]

In the words of the Communards, "Don't leave me this way...." lolol

 

[securespark]

Sounds like there is damage to the switch cable?

Shorting out between the L & Sw L causing the light to remain on even when the switch is detached.

There are definitely no nails through cables?

 

[EdR]

The switch cable is old and brittle and two wire only (no earth). The light socket back is wood. The old dimmer paradoxically was metal. The junction box looks like bakelite. The wires in the loft have earths which have been taped back away from the junction box. I can see no evidence of a nail on the switch wire. Perhaps time to add a new wire from switch to junction box with earth. I am guessing that if I do this I have to get an electrician to check it. They can also look at all the other stuff that slightly concerns me (wires under insulation etc.).

 

[ban-all-sheds]

If you've got brittle insulation, which (by the sounds of it) has failed somewhere, allowing wires to touch, then your wiring is very old, and very much past its use by date.

Features such as wooden back boxes and lack of earth tie in with it all being old.

What are the other cables like?

You'd be well advised to have it all checked over, and for now to leave it all alone. If you do have VIR cables then they could be in a parlous state, and any disturbance could cause the insulation to crumble, and if that happens you could end up with no power until the place is rewired. It may well need rewiring anyway, but the least amount of fiddling around with the wiring until that actually starts the better.

 

[flameport]

Lighting cables under insulation is not a problem.

If the cable has no earth, metal switches cannot be used. If it's brittle then probably rubber insulated, which should have been replaced several decades ago.

 

[OwainDIYer]

The switch cable is old and brittle and two wire only (no earth). The light socket back is wood.

That suggests very old wiring, pre-WW2, which is well overdue for replacement.

 

[GaryGarden]

If you've got brittle insulation, which (by the sounds of it) has failed somewhere, allowing wires to touch, then your wiring is very old, and very much past its use by date.

Features such as wooden back boxes and lack of earth tie in with it all being old.

What are the other cables like?

You'd be well advised to have it all checked over, and for now to leave it all alone. If you do have VIR cables then they could be in a parlous state, and any disturbance could cause the insulation to crumble, and if that happens you could end up with no power until the place is rewired. It may well need rewiring anyway, but the least amount of fiddling around with the wiring until that actually starts the better.

Surley Vulcanised India is all the rage in todays, must have, cheap & trendy from the far east world! Are you telling me this stuff is no good?

Joking aside i think the OP needs a full health check up on their internal wiring, an ECIR costs nothing when compared to a life and the results one can throw up can be astounding.

 

[EdR]

I have called an electrician. Thanks all.

 

[EdR]

I have been doing some more reading. The wires are definitely PVC. We still have a bakelite fuse box. I suspect that the wiring in the loft wand to the switches as probably replaced in the early 1960s. Apparently this early PVC is not as long lived as the modern stuff.

When we moved in, in the 1980s I remember replacing the roses and adding new pendants - the old ones had bare wire showing. A London Electricity man did a survey and added earthing to the mains, which (from memory) connected to the pipework in the house but was happy otherwise.

The lighting hasn't really needed attention until now.

 

[securespark]

Your lighting wiring (at the very least) is older than 1980's.
Lighting cables without earth wires in them date from the mid-60's at the earliest, but wooden back boxes can be even older.