How/why is my light switch wired like this?

BackyardDIY · 7 Jan 2017

Currently replastering and came across this while knocking the old plaster off. There are a number of things that strike me as being incorrect, but as a layman I don't really know, and the switch worked so what do I know?

Rather than entering the back box both the feed cable and the light cable were just buried in plaster, twisted together and held in place by the plaster (which they are now not, of course). What is really confusing me though is that both live wires are twisted together and connected to the common terminal - I thought the cable feed alone connected to this and that the switch live connected to the L1 terminal. Not only that but the wire that is actually connected to the switch terminal is connected to light cable's earth wire. The feed cable earth wasn't connected to anything, just buried in plaster. The two neutral wires from both cables are connected together, which I believe is correct. Admittedly the coloured plastic has deteriorated quite badly so I may be mistaken in what I'm seeing.

When I come to rewire this should I replicate the original wiring above or do it how I thought it should be done, ie like this:

Pigeon85 · 7 Jan 2017

Probably needed a longer wire and that was their solution (obviously the wrong choice)
Check to see if the wires are the wrong way around in the ceiling rose.

john4703 · 7 Jan 2017

It looks as if the feed is coming from below and the cable to the light goes up. You might be able to move the switch higher and terminate all the cables in the box but it looks like 3/029 and is therefore old and if you are re-plastering it would be best to rewire it in new cable,. If you are not 100% sure then ask an electrician for advice about the cable condition, it probably dates to the 1960s or earlier..

deadshort · 7 Jan 2017

Simple, it's wired like that to give the impression it's been rewired ! And boy, do you need rewired

DS

Spark123 · 7 Jan 2017

The cables don't appear to be PVC, are they lead? The inner insulation looks like VIR which has disintegrated.
Looks like you need a proper spark in before you bother re-plastering!

john4703 · 7 Jan 2017

Spark123 said:
The cables don't appear to be PVC, are they lead?

I missed that they are probably lead, makes them lots older that I thought.

Spark123 · 7 Jan 2017

The neutrals (in the chock block) are absolutely hanging!!
Getting an electrician in to do an EICR (electrical installation condition report) or just a basic probe about would be an idea to see what the rest of the installation is like. If it is up to this standard then a full re-wire will be called for.

endecotp · 7 Jan 2017

deadshort said:
Simple, it's wired like that to give the impression it's been rewired !

That was my thought too: there are stories of cowboys who claim to rewire a property but actually just replace the switches and sockets plus a few inches of wire. (A friend got a serious electric shock while removing "obviously redundant" wiring in a house that had been done like this.)

Have you looked at any of the other wiring?

Spark123 · 7 Jan 2017

If it is as bad as that it will probably fall to bits when trying to inspect.

Spark123 · 7 Jan 2017

Wasn't this electrician that rewired it was it?

john4703 · 7 Jan 2017

endecotp said:
there are stories of cowboys who claim to rewire a property but actually just replace the switches and sockets plus a few inches of wire.

I know of someone who bought a house and most of the nice new looking sockets were not working. An electrician was called. There was no wiring at all. Just surface mounted sockets fixed to the walls. No EICR in those bad old days.

BackyardDIY · 8 Jan 2017

Any idea why both lives are connected to the L1?

yorkspark · 8 Jan 2017

It's a loop in system, using the switch as opposed to the ceiling rose. Please don't tell us your going to continue using that obsolete and dangerous cabling, it's life expired by about 40years, the insulation has crumbled away exposing live conductors, the sheath looks to be lead, which won't appreciate been bent and pulled and will crack, possibly shorting together. Whilst you've all the plaster off you desperately need to rewire the lighting circuit if not the whole property.
It would appear the previous owner has pulled a fast one by fitting new plates and short cable extensions to shot cables, what condition is the consumer unit in?

BackyardDIY · 8 Jan 2017

I haven't got all the plaster off, it's just a small entrance way that needed doing, wasn't planning on replastering the entire house. :-/

Lectrician · 8 Jan 2017

You need a rewire! No point plastering and making things look nice with that wiring! Too often people plaster, decorate, tart their place up, ignoring the roof and wiring! Then comes the "we haven't got enough money". Start with the important things!

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How/why is my light switch wired like this?

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