Weird electrical problem

[GB]

I noticed a slight fizzling sound when I turned on the landing light. So, I undid the switch and had a look inside.

First of all, I should say it was a double switch. One side was for two way switching to the floor above, and the other side was three way switching for this floor. That's an awful lot of wires to cram into a back box, even quite a deep one.

Anyway, it turned out that two of the conductors were completely loose. They pulled out as soon as I eased the switch away from the wall. Also, the earth wire was loose, although it stayed in its terminal.

This switch was fitted in 1998, and AFAIK it had not been touched since. It has worked fine since then, and it's working now since I tightened it up. So, what's going on?

My guess is that it's all so congested with all those cables that it was never properly tightened in the first place. But, how come it's worked okay for 20 years?

[Jethro_uk]

Repeated mechanical shock of heating/cooling (exacerbated by arcing if the wires were loose to start with) leading to the screw slowly following the thread ?

[spuorgelgoog]

Brexit :-)

Anyway, the conductors have been loosening over time, but not so much to degrade the connection, until just now when critical level of resistance was obtained and it started fizzing.

Could even have been because it's colder today.

Owain

[Pancho]

Is that why, spring, wago style connectors are mandated for inaccessible junctions.

[Jethro_uk]

*shrug*

would make sense. Any threaded fastener will work lose when subjected to vibration - even very low frequency cycling of hot/cold in a house over

24 hours.

Hence split pins, loctite, nylox, punched nuts ....

[Adam Funk]

...and that's today's holy war started!

[Ray]

If it was that they'd all be loose in the house. None of mine are and they were done in 1972. Much more likely that whoever did that one forgot to tighten the screws and the contact was good enough to work fine for 20 years until repeated heating due to a less that tight contact ended up with too much corrosion and arcing.

[whisky-dave]

Yes, surely you shouldn't be using spring connectors in autumn.

[GB]

There can't be a lot of heating on a lighting circuit. I suppose there's a bit of vibration every time the switch is turned off and on.

[Jethro_uk]

Plus the natural cycling of ambient temperature during 24 hours.

Whether that is enough to have any noticeable effect is another matter.

[Brian Gaff (Sofa 2)]

Its the juxtaposition of the wires in the holes, then as the copper squashes eventually something gets unwedged and the connection is loose. Seen it on sockets as well. Indeed any electrical connection seems to suffer from this if there are multiple wires in a hole. Brian

[Ray]

There is with mine,, I used to use 150W PAR38s before I change to Hue leds,

Doesn?t explain why mine did much longer with no loosening.

[Tricky Dicky]

Can attest to screw connections working loose over time. I recently posted about a junction box I had installed on a floor joist about 5years ago only to find when I added a spur to it I found the screws gripping OK but definitely not tightened to my usual torque of one grunt + 1. At the moment it is easily accessible as the floor is carpeted but SWAMBO is talking about replacing the covering with Amtico or Karndean so will probably replace it with a Wago box before that.

Richard

[PeterC]

"'tis the Winter of our disconnect..."

[NY]

I bought lots of GU10 light fittings. Each one was supplied with a spring connector for the incoming wires, and permanent connections to the fitting.

The spring connectors were just about OK for single twin-and-earth solid-core wires: the springs retained the wires OK. But some of the existing fittings that I was replacing had two or even three sets of T&E going to the screw-terminal junction boxes. The springs were nowhere near strong enough to retain two or three solid-core wires: at least one wire would always pull loose.

I quickly learned that the spring connectors were not up to the job, so I cut each one off and used the existing screw-terminal junction boxes. Much more secure and certain to clamp all the wires - but I will check them every few years to make sure that the screws aren't working loose...

So I'm in the screw-is-better-than-spring camp ;-)

[Andy Burns]

An argument in favour of Wago connectors, with a hole per wire.

[Dave Liquorice]

I though wago and similar spring connectors were stricly 1 wire per hole. That fact that the larger sizes can accept more than one smaller wire was improper use. You might get away with two wires but three or more is asking for trouble.

[Andy Burns]

I'd say so.

[ARW]

Or fit an AFDD that does not work?

[gopalansampath]

Screw connections tend to loosen over temperature cycles, vibration in the frame ie.,a large "thud" of a tree felling, roadside rammer or even a mild land tremour. It would be a good practice to open and clear dust and use hot air from blower across terminals,AND, tighten them all once periodically, typically when we change smoke-alarm batteries