Odd lighting circuit wiring

[Lobster]

I'm just setting to on a complete rewire to sort out the hotchpotch of wiring I'm faced with... I disconnected the landing lightswitch yesterday (it had been working beforehand) to find that the switch cable consisted of one PVC-sheathed, red-insulated wire (wired to a switch terminal) and an uninsulated wire, protected by green earth-sleeving and wired to the metal socket box. Is this configuration even slightly safe and OK? How does it work?

(Probably irrelevant, but a second, normal T&E cable leaves the switch and disappears off downstairs - I think this is supposed to provide

2-way switching, although it actually serves to ensure the landing light only operates when the kitchen light is on...)

Thanks David

[Tim Mitchell]

In article , Lobster writes

Uhh? do you mean one terminal of the switch is connected to the red wire and the other terminal of the switch is earthed to the socket box? Or do you mean that the socket box is connected to an earth which comes down with the red wire?

And this cable, is this connected to the switch or what?

[usenet]

It doesn't work if only those two wires were connected. I suspect the other T&E was connected as well and fell off when you pulled the switch away from the box.

(Unless something *really* wierd is going on and the switch is faulty and is swtching from one of its terminals to the screws which hold it into the box and the earth wire isn't earth)

Are you saying this was connected to the switch as well? If so it sounds quite normal, a two-way switch with the third wire provided by the single sheathed red wire you describe above. It's commoner to use triple and earth but twin and earth plus a single is perfectly OK too.

If it's no longer a two-way switch then the other end has been wired up in a junction box or some such so that it's as if the other switch of the two-way pair is permanently in one position.

[Dave Plowman]

Having a green/yellow sleeved earth wire connected to the metal box is normal practice.

The single red wire you describe is either the feed into, or return from, a two way switched circuit - it will have been wired to the 'com' terminal of the switch. The two other wires from the TW&E will have been wired to the L1 and L2 terminals, and go to the same terminals of the other two way switch.

It's not the way I prefer to wire a two way switch circuit, but there's nothing wrong or unsafe about it. It's likely the other end that's wired wrong if the two way switching doesn't work.

[Lobster]

Ah, that could be along the right lines. 'Cept that the T&E cable heads downwards towards the downstairs switch, whereas the single red heads upwards towards the light!, rather than to the downstairs switch in parallel with the T&E. But like I say, the arrangement doesn't work anyway, so all bets are off. Just curious really; it's all coming out PDQ.

David

[Owain]

"Lobster" wrote | Ah, that could be along the right lines. 'Cept that the T&E cable | heads downwards towards the downstairs switch, whereas the single red | heads upwards towards the light!, rather than to the downstairs switch | in parallel with the T&E. But like I say, the arrangement doesn't | work anyway, so all bets are off. Just curious really; it's all | coming out PDQ.

Maybe the T&E is the strapping wires from the downstairs switch (from whence the live comes) and the single red is the switched live to the light, and the light borrows a neutral from 'somewhere handy'.

Owain

[usenet]

It could thus be the alternative way of wiring a two-way switch:-

------------------- / \ single red L ----o T&E o--------

------------------- to light

N -----------------------------------

Hope this is clear, it's shown in one of the 'on' positions.

[Christian McArdle]

Except that it is deprecated because it forms an inductive loop, which can interfere with hearing aids. Loops in wiring installations should be avoided, except ring final circuits, which have balanced impedences to ensure reasonably balanced current flows, provided no terminals become undone, or conductors broken.

Christian.

[Dave Plowman]

Right. But running 'straps' was a common way with some pro electricians.

[Christian McArdle]

And still is, in some cases.

Christian.

[chris French]

In message , Martin Angove writes

I supply both my hall and landing lights from the same circuit, both of which are two way switched. (In my case the upstairs lighting circuit as this was more lightly loaded). For the hall light run a feed down to the landing switch, then a drop to the hall light, with 2x3 core and earth to the hallway switches.

Suitably labelled at the CU of course

[Lobster]

Interesting, because when I rewire my circuits shortly, I'm going to be in the same position, and this issue hadn't occurred to me (yet!)

In my case, I was going to use 2G2W switches both upstairs and downstairs; the switch on the landing supplying the bathroom and the landing, and the downstairs switch supplying the kitchen (where the stairs start) and the landing. So the 'official' way would be to wire these would be as Martin describes above? (I'll be getting the installation checked by an electrician, so 'official' is what I'm after!)

David

[Martin Angove]

When I said "official" all I was referring to was the 2-way switching arrangement to be found in the On Site Guide (p55). Although this is the IEE's recommended arrangement, it is not the only one which complies with regulations.

As far as I can tell, there is no guidance about the need to keep different circuits of the same voltage separate within (for example) a multigang switch, but I would suggest that common sense would lead most people to reduce this likelyhood as much as possible. In my case, with the two gang, two way switching question (hall & landing) I would say that either both lights could somehow be supplied from the same circuit (means running an extra supply wire somewhere) or two single-gang switches could be used instead of a two-gang, or a warning could be left in an "obvious" place. This might be some kind of label attached to the CU or possibly even in the backbox of the light switch(es) in question.

HTH.

Hwyl!

M.