At http://www.diydoctor.org.uk/projects/lights_and_switches.htm (very
near the bottom of the page) there are two two-way lighting circuits
represented in diagramatic form.

Is one preferred? The second one to me looks simpler. Between the
switches all you need is two-core (plus earth). On the other hand, the
default example given in most manuals seems to be the first one, which
requires three-core (plus earth).

Why would anyone choose the first one over the second? The only
difference I can see is the connection between the two switches, and in
the second case it looks more complicated.

Actually having drawn them both out on paper a few times I can see
another difference: the first version goes (more or less):

live - switch 1 - switch 2 - light

and the second goes:

live - switch 1 - light
|
|
-- switch 2

which might make it easier in some circumstances...

Would a house with older (i.e. cloth-covered) wiring be more likely to
use one form over the other?

Many thanks for any advice or answers.

Daniele

Daniele

You should use the version that has the three core cable between
switches simply because anyone else who looks at the circuit in the
future will understand what is going on. There are no real problems
with the second form of the circuit, but why not go the conventional
route when the cost and complexity of the two are pretty much the same.
Three core and earth in harmonised colours (grey, brown and black
instead of red, yellow and blue) is available from screwfix. You do
need to check which new colour is equivalent to which new colour as I
can't remember off the top of my head, but you should get this easily
enough somewhere on the web.

Before anyone else gets the chance to say it, if you have a circuit
with cloth covered wire, you should think about how old it is likely to
be and consider complete replacement. In my personal experience with
old circuits (in my case lead sheathed 1920's wiring with no earth) it
is best not to alter them unless by complete replacement.

Fash

D.M. Procida wrote:
At http://www.diydoctor.org.uk/projects/lights_and_switches.htm (very
near the bottom of the page) there are two two-way lighting circuits
represented in diagramatic form.

Is one preferred? The second one to me looks simpler. Between the
switches all you need is two-core (plus earth). On the other hand, the
default example given in most manuals seems to be the first one, which
requires three-core (plus earth).

Why would anyone choose the first one over the second? The only
difference I can see is the connection between the two switches, and in
the second case it looks more complicated.

Actually having drawn them both out on paper a few times I can see
another difference: the first version goes (more or less):

live - switch 1 - switch 2 - light

and the second goes:

live - switch 1 - light
|
|
-- switch 2

which might make it easier in some circumstances...

Would a house with older (i.e. cloth-covered) wiring be more likely to
use one form over the other?

Many thanks for any advice or answers.

Daniele

D.M. Procida wrote:

Actually having drawn them both out on paper a few times I can see
another difference: the first version goes (more or less):

live - switch 1 - switch 2 - light

and the second goes:

live - switch 1 - light
|
|
-- switch 2

The second one is the "standard" one, and is very easy to wire - you
wire the switch closest to the lamp using L1 and L2 as live in and
switched live out - and then run three core and earth to the next switch
strapping all three connections to their counterparts in the switch.

This second circuit keeps the current flowing up and down separate
conductors in the strap cable, which is preferable for reducing
interference with other electronic and electrical systems (particularly
things like inductive loop systems for hearing aids).

It actually looks much simpler if you draw it thus:-

N_____________________________________
|
L_______________ ______________ |
| | | |
| | | |
| | | |
| | \X/ LAMP
| |
L1 L2
SW1 |\ |
| C |
| | |
| | |
| | |
| | |
| | |
| C |
SW2 | \|
L1 L2



Would a house with older (i.e. cloth-covered) wiring be more likely to
use one form over the other?

Who cares - it needs rewiring as a matter of urgency!

--
Cheers,

John.

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| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

John Rumm wrote:

and the second goes:

live - switch 1 - light
|
|
-- switch 2

The second one is the "standard" one, and is very easy to wire - you
wire the switch closest to the lamp using L1 and L2 as live in and
switched live out - and then run three core and earth to the next switch
strapping all three connections to their counterparts in the switch.

It actually looks much simpler if you draw it thus:-

Thanks, it does.

Next questions -

1. the old switches aren't earthed - they aren't in a metal box,
just in a little cavity hacked in the brick wall, and the switches have
no earth terminal in them. Therefore any earth cable to the switches
wouldn't actually have anything to connect to... How important is it to
have an earth to the switches?

This is an issue because though the downstairs switch is reasonably
accessible and could be so earthed if necessary, the upstairs one would
probably require a lot of hacking at plaster and black mortar to do
that, and likely tearing the loft to pieces as well. So if it's not
deemed absolutely necessary it might be much easier not to do it.

2. This is actually a two-gang two-way system - two switches both
up and downstairs for hall and landing lights:


L N L N
| | | |
L1 L2 L1 L2
SW1 |\ | |\ | SW1
| C | | C |
| | | | | |
| | | | | |
| | | | | |
| | | | | |
| | | | | |
| C | | C |
SW2 | \| | \| SW2
L1 L2 L1 L2

Would it be OK to leave out L1-L1 on the right-hand pair of switches,
and simply take a little jumper from L1 from the left-hand one in each
case? It would save additional cable in some very tight cable spaces if
so.

Would a house with older (i.e. cloth-covered) wiring be more likely to
use one form over the other?

Who cares - it needs rewiring as a matter of urgency!

That was what I thought - the electricians were much much more relaxed
about it than me, and so apparently was the inspector who came round.

Thanks again,

Daniele

On Sat, 25 Feb 2006 09:09:10 +0000 someone who may be
(D.M. Procida) wrote
this:-

1. the old switches aren't earthed - they aren't in a metal box,
just in a little cavity hacked in the brick wall, and the switches have
no earth terminal in them. Therefore any earth cable to the switches
wouldn't actually have anything to connect to... How important is it to
have an earth to the switches?

If the switches are plastic, not important at all. However, whether
it is important or not is irrelevant, it is a requirement. It is a
requirement for the important reason that if someone was to change
the switch an earth connection may be necessary.

This is an issue because though the downstairs switch is reasonably
accessible and could be so earthed if necessary, the upstairs one would
probably require a lot of hacking at plaster and black mortar to do
that, and likely tearing the loft to pieces as well.

If the existing cable is going to be replaced then what great
difference does the presence or absence of a protective conductor
make to the amount of hacking and tearing?


--
David Hansen, Edinburgh
I will *always* explain revoked encryption keys, unless RIP prevents me
http://www.opsi.gov.uk/acts/acts2000/00023--e.htm#54

In article
,
D.M. Procida wrote:
Is one preferred? The second one to me looks simpler. Between the
switches all you need is two-core (plus earth). On the other hand, the
default example given in most manuals seems to be the first one, which
requires three-core (plus earth).

Why would anyone choose the first one over the second? The only
difference I can see is the connection between the two switches, and in
the second case it looks more complicated.

The big snag with the second way is it requires connection to the ceiling
rose from both switches - and only uses one cable from each.

Normally, the switch pair goes to only one switch, so the preferred method
is run to the next one in Triple and Earth.

The second way was, however, common many years ago when wiring was run
using single core rubber covered wiring.

--
*Very funny Scotty, now beam down my clothes.

Dave Plowman London SW
To e-mail, change noise into sound.

"D.M. Procida" wrote in
message
...
At http://www.diydoctor.org.uk/projects/lights_and_switches.htm (very
near the bottom of the page) there are two two-way lighting circuits
represented in diagramatic form.

Is one preferred? The second one to me looks simpler. Between the
switches all you need is two-core (plus earth). On the other hand, the
default example given in most manuals seems to be the first one, which
requires three-core (plus earth).

Why would anyone choose the first one over the second? The only
difference I can see is the connection between the two switches, and in
the second case it looks more complicated.

Actually having drawn them both out on paper a few times I can see
another difference: the first version goes (more or less):

live - switch 1 - switch 2 - light

and the second goes:

live - switch 1 - light
|
|
-- switch 2

which might make it easier in some circumstances...

Would a house with older (i.e. cloth-covered) wiring be more likely to
use one form over the other?

Many thanks for any advice or answers.

Daniele

I prefer bottom (2nd) layout and use 3-core + Earth between 2-way switches.
Both toggles should be up to make Lamp Off, if/when the pair is wired
correctly.
One day, you may want to achieve 3-way switching, simply by inserting in the
3+E wiring path an Intermediate switch (4 terminals) whereby L1 and L2
status lines are inverted.
Jim

In article ,
Jim Gregory wrote:
I prefer bottom (2nd) layout and use 3-core + Earth between 2-way
switches. Both toggles should be up to make Lamp Off, if/when the pair
is wired correctly. One day, you may want to achieve 3-way switching,
simply by inserting in the 3+E wiring path an Intermediate switch (4
terminals) whereby L1 and L2 status lines are inverted.

Makes no difference which method is used as regards later fitting of an
intermediate.

--
*If a pig loses its voice, is it disgruntled?

Dave Plowman London SW
To e-mail, change noise into sound.

D.M. Procida wrote:

Next questions -

1. the old switches aren't earthed - they aren't in a metal box,
just in a little cavity hacked in the brick wall, and the switches have
no earth terminal in them. Therefore any earth cable to the switches
wouldn't actually have anything to connect to... How important is it to
have an earth to the switches?

Not having an earth is ok so long as you have no light switches or
fittings with exposed metal parts.

Note that the regulations are not retrospective either - so there is no
requirement to change existing installations to match new requirements
unless you are rewiring or making significant changes to them.

2. This is actually a two-gang two-way system - two switches both
up and downstairs for hall and landing lights:


L N L N
| | | |
L1 L2 L1 L2
SW1 |\ | |\ | SW1
| C | | C |
| | | | | |
| | | | | |
| | | | | |
| | | | | |
| | | | | |
| C | | C |
SW2 | \| | \| SW2
L1 L2 L1 L2

Would it be OK to leave out L1-L1 on the right-hand pair of switches,
and simply take a little jumper from L1 from the left-hand one in each
case? It would save additional cable in some very tight cable spaces if
so.

(Note for completeness - remember that what you have shown as "N" above
is still a live - the switch out connection)

The implication of doing that is that you are sharing a live feed
between both up and downstairs lights. If there is only one lighting
circuit for the whole house then this would be ok. If however you have
up and downstairs on two separate circuits then it would be unwise to do
this since each floors lamp out to be powered from the appropriate circuit.

The reality would normally be slightly different from the way you drew
it with two circuits:


Landing Light Hall Light

L SW out
| |
L1 L2 L1 L2
SW1 |\ | |\ | SW1
| C | | C |
| | | | | |
| | | | | |
| | | | | |
| | | | | |
| | | | | |
| C | | C |
SW2 | \| | \| SW2
L1 L2 L1 L2
| |
L SW Out


So the power feed for the landing light comes from upstairs and the feed
for the hall comes from downstairs.

Would a house with older (i.e. cloth-covered) wiring be more likely to
use one form over the other?

Who cares - it needs rewiring as a matter of urgency!


That was what I thought - the electricians were much much more relaxed
about it than me, and so apparently was the inspector who came round.

The electrician was probably thinking "not my house" and the inspector
would not be in a position to comment unless you just had the circuit
installed like that!


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/