Smoke and sparks at light switch

[Valedictor]

Hi all,

I just fitted a new wall light in a downstairs bathroom. Turned the mains electric back on, and turned the light switch on.

Light came on, no problems.

About 10 minutes later, I then switched the light off at the wall. As I did it, a wisp of smoke came out of the crack where the switch sits. I could see some sparking too.

Turned the electric off at the mains immediately.

My father and I then checked inside the light switch for damage, and also at the point where we wired the light to the wall. Couldn't see any sign of damage in the light switch despite the smoke and sparks.

When we checked the wiring at the light fixture end, we noticed that the two wires had sort of fused together (insulation melted perhaps?) So we are assuming that that is what caused the problem. Why would it start smoking when I turned it off? Wouldn't it have started when we turned it on in the first place? We just asked at our local lighting shop, and they seem to think that the electricity arced between the wires at the fixture end. If so, why did it start smoking at the light switch end?

Where do we stand now? Does the light switch need replacing, or is it just a matter of ensuring that the wires are intact and not in contact with each other and reconnect things again? Or is the whole thing too badly damaged?

We are not going to touch anything until an electrician looks at it now. I just wanted to know what sort of damage has been done so I am a bit better informed when the electrician gets here.

I have an electrician scheduled to do a full rewire in December. We thought we could tackle this job ourselves though, as it just looked like a matter of removing the old ceiling mounted light, and connecting the two wires to the new wall mounted light. Won't be trying that again!

Thanks, John.

 

[BigJon]

It could be when you turned your switch on, you were connecting/switching live to neutral across the switch because the cables at the light were fused together if you get my drift . You could try repairing the "fused" cables at your light ( re-bare and reconnect ) and do the same at the switch and try again, The switch may be damaged, if you have an old switch at hand you could try that to prove its the switch at fault and not your light fitting/wiring. Remember to turn the power off when re connecting and checking your connections etc

 

[Spark123]

How many cables and wires were there in the light and how did you connect them. A common mistake to make is to connect the switched live to the neutral hence when the switch is closed there is a dead short.

 

[breezer]

but the poster said the light came on.

my guess is cables to actula lamp too small csa, and current mleted them

 

[JohnD]

I was thinking maybe loose wires in terminals, overheated.

 

[Spark123]

but the poster said the light came on.

my guess is cables to actula lamp too small csa, and current mleted them

Yep, with a switch wired across phase & neutral providing the switch is open the light will come on when the circuit is energized, it will go bang when the switch is closed though .

 

[breezer]

yes, agreed, but to do that it would mean having all 4 wires in the switch, and not account for the wires at the light melting.

Valedictor, how did you wire the switch?

 

[RF Lighting]

neutrals to L2 perhaps

A friend of mine did this.

I laughed at him.

Alot.

 

[Spark123]

yes, agreed, but to do that it would mean having all 4 wires in the switch, and not account for the wires at the light melting.

Valedictor, how did you wire the switch?

Nope, not necessarily , the favorite one is to remove a loop in ceiling rose etc at the light and replace it with a 3piece of terminal block, all reds to one side, earths to the middle and all blacks to the other. The switch cable, once closed is then a dead short across the supply. The fact the OP has been changing a light sets these alarm bells ringing .
The melting above the light could be pre-existing or caused by a high resistance joint etc, the fuse** should have disconnected the circuit before this happened in the event of a dead short. (**providing there was fuse wire in the fuse holder )

 

[slippyr4]

Nope, not necessarily , the favorite one is to remove a loop in ceiling rose etc at the light and replace it with a 3piece of terminal block, all reds to one side, earths to the middle and all blacks to the other.

But the OP said "Turned the mains electric back on, and turned the light switch on. Light came on, no problems. ".

If he'd wired the switch accross P+N then the light would have come on when he turned the electric back on.

The fact that the switch actually turned the light on (the first time) implies that it's wired (mostly) correctly.

 

[Spark123]

I'd take that with a pinch of salt, without the additional information such as he amount of cables and how they are connected it is impossible to tell.

 

[HDRW]

I'd take that with a pinch of salt, without the additional information such as he amount of cables and how they are connected it is impossible to tell.

Indeed, if he'd put Neutral into L2 and there's something wrong with the fusing (the nail may be rusty, giving high resistance! ), it could have been cooking for a few seconds before he switched it on, but he didn't notice until he switched it "off" again.

Cheers,

Howard

 

[slippyr4]

I'd take that with a pinch of salt, without the additional information such as he amount of cables and how they are connected it is impossible to tell.

Indeed, if he'd put Neutral into L2 and there's something wrong with the fusing (the nail may be rusty, giving high resistance! ), it could have been cooking for a few seconds before he switched it on, but he didn't notice until he switched it "off" again.

Cheers,

Howard

Good point. A lesson learned: always use galvanised nails for replacement fuses.

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Point of information:
This is a joke. Never use anything but the correct cartridge or fuse wire.

Mod Rupert
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