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

[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,