Garage Lighting question

[pz8l8t]

Hi Guys,
Wondering if anybody can help me. I am trying to figure out how my builder has laid the wires the light in the garage. He's done one, and left the jobs. The design for the light is a 2 way lighting circuit whereby the light can be switched on or off at either end of the garage.

This is what I see:

In the switch at one end of the garage there are 2 twin and earth cables going up. Same for the switch at the other end of the garage. In the ceiling there are 4 wires and it looks like 2 switch cables.

I intend going up into the roof space tonight to confirm this, but in the meantime I was wondering if anybody is familar with this type of wiring.
Thanks in advance

 

[rebuke]

My *guess* would be that one bit of T&E runs from one switch to the other, and should link L1-L1, L2-L2 (or L2,L3 if the switch has l1,l2,l3). The other T&e is then simply acting as a switch wire with a spare core, so the permanent live will go in to C (or l1 if l1,l2,l3) one switch, and the switched live comes back from C (or l1 etc) on the other.

It's an unusual way to do it, but if your builder didn't have any 3C+E cable, then it is one way of doing it.

Note however that it is not the only way he could be intending to wire it, so don't assume this is correct - there are a number of other ways it could be wired with this number of cables...

 

[pz8l8t]

My *guess* would be that one bit of T&E runs from one switch to the other, and should link L1-L1, L2-L2 (or L2,L3 if the switch has l1,l2,l3). The other T&e is then simply acting as a switch wire with a spare core, so the permanent live will go in to C (or l1 if l1,l2,l3) one switch, and the switched live comes back from C (or l1 etc) on the other.

It's an unusual way to do it, but if your builder didn't have any 3C+E cable, then it is one way of doing it.

Note however that it is not the only way he could be intending to wire it, so don't assume this is correct - there are a number of other ways it could be wired with this number of cables...

Thanks for the response. That does make sense but I cannot work out why there is 4 wires coming out the ceiling. My guess is that there are 2 switch wires and 2 for the loop.

By your explanation i'm guessing that because he didn't use 3-core and earth, the only way to get live and netural would be to wire 2 switch cables to the rose connected to the same point and use the spare wire going from switch to switch as the switched live to each switch leaving a redundant core as you stated.

This makes some sense now if that is correct? I'm intending to go into the roof space tonight to check where the wires are going from each switch.

 

[rebuke]

4 wires coming out the ceiling is entirely possible, as you say two for the loop (1 in, 1 out), and then the two wires I described one going to each 2-way switch, each of those having one redundant core.

Obviously though, check and make sure you understand exactly which each cable is, otherwise it could all go bang...

 

[ColJack]

it's the old 2-plate method..
used in old houses and in installations with conduit and singles..
it's illustrated by the top left diagram in the following picture..

 

[pz8l8t]

Thanks for the response guys. Its become much clearer now. The wiring is the same as 3-core and earth (at the switch) only the live and neutral come from the rose to each switch, with COM coming from the cable running between switch to switch with a redunant core.

 

[ColJack]

are you saying that IS what's happening, or that is what you THINK is happening?

//www.diynot.com/wiki/electrics:two-way-lighting

 

[rebuke]

What you've described sounds wrong/impossible...

Firstly, why is the neutral even at the switches - it's only needed at the rose, and if each switch has live+neutral, with a single core between the switches, where is the switched live that you need at the rose?

 

[pz8l8t]

again, thanks for the resonse guys. this is how I understand it. if it was 3 core and earth being used: 3 cables at the rose loop in, loop out, switch. At the first switch would be the switch cable at the rose + a 3 core and earth going to the other switch. the switch cable at the rose would go into this switch as live to l1 (brown wire), neutral to l2 (blue wire) and the 3 core would be live to l1 (brown wire), netural to l2 (grey wire), switched live to com (black wire).

On the other switch which would have just the 3 core and earth it would be live to l1 (brown wire), neutral to l2 (grey wire), switched live to com (black wire).


Now my interpetion of what you guys have said is as follows:

switch 1 -> 2 wires, 1 going to rose, 1 going to other switch

wire going to rose -> live to l1, neutral to l2
wire going to other switch -> brown wire into com neutral redundant.

switch 2 -> 2 wires, 1 going to rose, 1 going to other switch

wire going to rose -> live to l1, neutral to l2
wire going to other switch -> brown wire into com neutral redundant.

Is this interpetation wrong?

 

[rebuke]

Your understanding is wrong - you don't send the neutral to the switch at all. If you look at the diagrams in the wiki, they show it quite clearly (just remember that a blue/black wire is not always neutral, it can be a switched live).

Diagram from the wiki:

At the first switch, the permanent live is connected to L1, and due to the 3C+E is also connected to L1 at the other switch. The C terminals are connected by a strapper (the black wire), and L2 is connected to the switched live (grey wire from the 3C+E and the blue wire at the first switch, this is NOT a neutral).

It sounds like your builder has set up this arrangement:

The T+E between the switches are the two wires at the bottom, and he's using one core from each of the T+E feeds to the switches going to the C terminal. But, as said, this is only a guess...

 

[ban-all-sheds]

Wondering if anybody can help me. I am trying to figure out how my builder has laid the wires the light in the garage. He's done one, and left the jobs.

What are you going to do about the hole you are now in with Building Control?

 

[pz8l8t]

Again, thanks for the reply. You are right. When I said neutral I meant it by the colour of the wire. In technical terms it's the switched live from the rose as you say. Sorry for the confusion here.

I'm still trying to figure out your diagram and explanation. But would my understanding also work (described again in the correct technical terminology)

At rose -> 2 switch wires -> both brown's connected to permanent live -> both blue's connected to switched live

switch 1 wire from rose -> brown connected to l1 -> blue connected to l2

switch 1 wire to other switch -> brown connect to com -> blue not needed



switch 2 wire from rose -> brown connected to l1 -> blue connected to l2


switch 1 wire to other switch -> brown connect to com -> blue not needed

 

[pz8l8t]

Wondering if anybody can help me. I am trying to figure out how my builder has laid the wires the light in the garage. He's done one, and left the jobs.

What are you going to do about the hole you are now in with Building Control?

He has only channelled the wires. He was supposed to get an electrician in to connected everything up and certify. I guess I have to look for one that's willing to do the job.