Converting 2 gang 1 way and 1 gang 1 way switches to 3 gang 2 way

[Luka]

I need to covert 2 gang 1 way and 1 gang 1 way switches to 3 gang 2 way. Switches needs to stay where they are but I can run cables between them. Is anything wrong with doing it as seen in the picture below? I did not include earth cable but both boxes are grounded.

 

[westward10]

That is not going to work.

 

[littlespark]

For a pointer…. Every connection should have at least one cable in it.

Are the lives at each switch position on the same circuit?

It can be done by running only 3 x twin and earth cables between the switches.

 

[Luka]

For a pointer…. Every connection should have at least one cable in it.

Are the lives at each switch position on the same circuit?

It can be done by running only 3 x twin and earth cables between the switches.

At the moment switch 1(2 gang) is fed by 3+E and switch 2 (1 gang) is fed by T+E. All lights are in the same circuit

 

[westward10]

As @littlespark said each terminal needs a wire in it linking to the other switch.

 

[Luka]

As @littlespark said each terminal needs a wire in it linking to the other switch.

I think I got it (at least I hope). Will it work ok if in addition to what I uploaded I just connect connect L2' s between switches the same way as I connected L1's and com's and use 3 x T+E cables for that?

 

[littlespark]

Hmm. No

I’m trying not to fall foul of the “no step by step instructions” forum rules…. But it’s really difficult without just telling you how to do it.

Would it help by explaining how a two way switch operates?
It’s merely a changeover switch. Rather than on/off it switches between L1 and L2

For a simple one gang switch at each location…
A live feed into the Common of one switch, a pair of cables linking L1 and L2 at one switch to L1 and L2 at the other switch, then the switched live going to the light from the Common of the second switch.

Now apply that explanation into your scenario.

 

[Avo Mk8]

To be fair to the OP, it looks as if the style of two way switching is intended to be as below.

If all lights involved are indeed on the same circuit, what's been drawn in post #1 is not incorrect, but it is incomplete.
A link has been missed on the left 3 gang, and two links missed on the right 3 gang.
Maybe I'm misunderstanding what's meant in post #6, but that mention of interconnecting L2's (just at each gang, not between locations) is essentially what's missing!

The subsequent wiring between the two locations could surely be done either by 3 off T&E, or by 2 off 3-core & E, but colours wouldn't be quite as illustrated in post 1

 

[littlespark]

The way I was thinking, avo, was that the live and switchwires are at different switches.

Then it’s just the new twins inbetween being used as the strappers.

 

[Avo Mk8]

The way I was thinking, avo, was that the live and switchwires are at different switches.

Then it’s just the new twins inbetween being used as the strappers.

I was just thinking all L2's can be supplied with Live without running anything between locations.
You are just left with 3 x com and 3 x L1 to run.

Maybe that suggestion doesn't help!

 

[Luka]

Hmm. No

I’m trying not to fall foul of the “no step by step instructions” forum rules…. But it’s really difficult without just telling you how to do it.

Would it help by explaining how a two way switch operates?
It’s merely a changeover switch. Rather than on/off it switches between L1 and L2

For a simple one gang switch at each location…
A live feed into the Common of one switch, a pair of cables linking L1 and L2 at one switch to L1 and L2 at the other switch, then the switched live going to the light from the Common of the second switch.

Now apply that explanation into your scenario.

Thanks but I am afraid I am unable to do it this way as I cannot rewire cables in walls. Live and switched live cables have to stay where they are (switch 1 for light 1 and 2, switch w for light 3), so I am essentially trying to add a second switch to each of existing gangs

 

[Luka]

Thanks, I think you are bang on what `I am trying to achieve. I missed interconnecting L2's in my original post. I have corrected that now. Is below drawing ok?

 

[brianmoooore]

There is a permanent live to connect to L2 of all switches already in place, so you will need three strappers to connect the 'coms' of all three switches to the 'coms' of the other three switches and three wires to connect the L1s of the three of the switches that are not near the feed to the light they control to the L1s of the other three switches that are.
Six wires in total between switch positions.

 

[Luka]

I was just thinking all L2's can be supplied with Live without running anything between locations.
You are just left with 3 x com and 3 x L1 to run.

Maybe that suggestion doesn't help!

Do you mean just bridging all 3 L2's in switch 1 from 3+E and all 3 L2's in switch 2 from t+e and then just interconnect L1's and coms between 2 switches using 2 x 3 core cable instead of 3?

 

[brianmoooore]

I hadn't seen Avo Mk8's post when I wrote my last post. We've both written the same thing.
Yes, feed the L2s with the 'live' already present near them, then 6 wires between the two sites. These can be 2 x 3&E or 3 x T&E.
What none of them can be is a repurposed earth wire.

 

[Luka]

Like that?

Do I need to connect earth wires in the strappers to terminals in the back boxes or can I leave them loose?

 

[Luka]

I hadn't seen Avo Mk8's post when I wrote my last post. We've both written the same thing.
Yes, feed the L2s with the 'live' already present near them, then 6 wires between the two sites. These can be 2 x 3&E or 3 x T&E.
What none of them can be is a repurposed earth wire.

Like that?

Do I need to connect earth wires in the strappers to terminals in the back boxes or can I leave them loose?

 

[brianmoooore]

That appears correct. All earth wires must be connected at at least one end to the incoming earth wire, which should be tested to confirm it does actually connect to the supply earth terminal. It is preferable that they're connected at both ends.
It should also be confirmed that both incoming lives are actually part of the same circuit.

 

[Luka]

That appears correct. All earth wires must be connected at at least one end to the incoming earth wire, which should be tested to confirm it does actually connect to the supply earth terminal. It is preferable that they're connected at both ends.
It should also be confirmed that both incoming lives are actually part of the same circuit.

100% the same circuit in the CU. Cant I just use for example 3 core YY cable instead of 3+E? Both boxes are already grounded by feeding cables

 

[littlespark]

Not the way I was thinking…. But it looks like it would work.

 

[DefyG]

Cant I just use for example 3 core YY cable instead

No for reasons stated in #16 as one of them will be insulated green and yellow and the cable itself should contain a cpc or earth conductor.

 

[Luka]

No for reasons stated in #16 as one of them will be insulated green and yellow and the cable itself should contain a cpc or earth conductor.

My point is... do I even need to run earth conductors between boxes or 6 wires between L1's and com's would be enough? Will I be actually achieving anything doing that if both boxes are already grounded?

 

[DefyG]

My point is... do I even need to run earth conductors between boxes or 6 wires between L1's and com's would be enough? Will I be actually achieving anything doing that if both boxes are already grounded?

Yes, the cables between the switches should include an earth conductor that is terminated at at least one end but preferably both ends, ie both switch boxes per post#18

You could run them in an earthed conduit but probably more troublesome!

 

[Avo Mk8]

Like that?

View attachment 121524

Do I need to connect earth wires in the strappers to terminals in the back boxes or can I leave them loose?

Just to confirm your latest diagram does match what's been discussed, and should work!
Don't ignore the guidance given here about earth conductors - Include them to comply with the regs, e.g. use T&E to do the cables between the two locations.

 

[Luka]

Just to confirm your latest diagram does match what's been discussed, and should work!
Don't ignore the guidance given here about earth conductors - Include them to comply with the regs, e.g. use T&E to do the cables between the two locations.

Will do. And I appreciate there are regs and they have to be followed, which Im giing to do. Only trying to find a justification, I guess I just like to know a reason I do something. I wonder if anyone actually knows what is achieved in this case by running earth conductors to already grounded boxes and why it needs to be done (except regs of course )

 

[littlespark]

the earth conductor within a twin and earth cable is known as a cpc... a circuit protective conductor...

The idea is, that IF damage is caused to that cable, ie, a screw put into a cable when it is buried in the wall, there is a chance that it catches a live conductor AND the cpc.... thus causing a short and operating the protection device at the board.

Without it, this hypothetical screw would become live,

 

[Luka]

the earth conductor within a twin and earth cable is known as a cpc... a circuit protective conductor...

The idea is, that IF damage is caused to that cable, ie, a screw put into a cable when it is buried in the wall, there is a chance that it catches a live conductor AND the cpc.... thus causing a short and operating the protection device at the board.

Without it, this hypothetical screw would become live,

Got it. Makes sense. Thanks.
Thanks to all you guys for your input