Odd lighting circuit wiring


L

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
 
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T

Tim Mitchell

Lobster said:
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?
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?
(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...)
And this cable, is this connected to the switch or what?
 
U

usenet

Lobster said:
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?
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)

(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...)
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.
 
D

Dave Plowman

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...)
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.
 
L

Lobster

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.
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
 
O

Owain

| 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
 
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U

usenet

Lobster said:
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.
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.
 
D

Dave Plowman

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

Martin Angove

In message <1077570991.81183.0@dyke.uk.clara.net>,
Owain said:
| 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'.
FWIW (n days later) that's exactly the way it is done in the house we're
currently ripping to bits. The worst part about it, as far as I can
tell (induction loops aside), is that you can end up with live from
*two* circuits in the same ceiling rose. In our case, the landing light
is controlled, as one might expect, from both top and bottom of the stairs.
The bottom switch sends a live up one or other leg of a bit of T&E. This
live is sourced (as far as I can tell) from the *downstairs* lighting
circuit.

The T&E goes to the L1 and L2 terminals of the upstairs switch, and then
a single&earth carries on upwards to the landing light, terminating at
its "switched live" terminal.

As you say, this means that the landing light needs a neutral from
somewhere, and this it gets from the upstairs lighting circuit, which
loops through the rose in the normal way!

In other words, when the light is on, the live on the SL terminal comes
from the *downstairs* lighting circuit, and the live on the "loop"
terminal from the *upstairs*.

This could lead to the dangerous situation where you want to work on the
light, and switch off the upstairs breaker. Realising that the light
still works (its live comes from downstairs and the breaker doesn't
switch the neutral) you then switch off the downstairs breaker,
switching the other back on so that you can at least have some light in
the house... or, I suppose, you could switch off the upstairs breaker,
not bother checking that the light doesn't work, and carry on happily
until someone inadvertently flips one or other of the switches. Either
way, a Nasty Shock (tm) awaits.

A similar problem arises with the other way of doing things, if you
happen to use a 2-gang switch in either location. For example you may
have a 2-gang switch at the bottom of the stairs to control both the
landing and the hall light. Wiring things the "official" way leads to
one switch being in circuit with the downstairs lighting, and the other
the upstairs. In order to work safely on the switch you would need to
realise this and isolate *both* circuits.

I would still prefer to do things this latter way as

* I expect odd things in the back of switches.

* most homeowners wouldn't bother changing a lightswitch, though they
may well want to change the light fitting.

* unless you'd met it before it is not expected that power in the rose
comes from two different circuits.

Hwyl!

M.
 
C

chris French

Martin Angove said:
A similar problem arises with the other way of doing things, if you
happen to use a 2-gang switch in either location. For example you may
have a 2-gang switch at the bottom of the stairs to control both the
landing and the hall light. Wiring things the "official" way leads to
one switch being in circuit with the downstairs lighting, and the other
the upstairs. In order to work safely on the switch you would need to
realise this and isolate *both* circuits.
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
 
L

Lobster

chris French said:
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.
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
 
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M

Martin Angove

In message <5a5ee072.0402290156.37cddf18@posting.google.com>,
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!)
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.
 

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