Best practice when changing two 1-gang 1-way switches to one 2-gang (still 1-way) – image attached

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Hi there. I’ve used this site and found it invaluable for a lot for my DIY projects… but this is the first time I’ve actually posted!

I feel comfortable to undertake a ‘cosmetic switch faceplate update’, but I want to make sure that I don’t breach any regs (or safety standards) in the change from two 1-gangs to one 2-gang set-up, so advice is appreciated.

The lounge in my 1987-build house still has its builder-original switch plates, which I want to update. Currently installed are two fittings: a ceiling light and a wall light, each being one-way. Each light fitting is switched on/off via a single gang (plastic) switch; the two switches sit adjacent to each other in a metal back-box that is sized/styled specifically for taking two, adjacent single switch plates. Each switch has three T&E cables into it – see this image:

To clarify, wiring (1.5mm) pattern is identical for each of the switches, as follows:

Two reds to two screwless ports marked “Common” and one red to the screwless port marked “1-way”; three blacks to one chock-block (left loose in the back box); three bare earths (sleeved) to the earthing terminal on the backbox. There is one earth terminal on each side of the back box to serve each of the switches.

I intend to have both lights still independently switched on/off (1-way), but want to swap the existing set-up to a single switch with 2 rockers. I will take out the old back-box and make good as necessary, and fit a deeper (35mm) back-box to aid wire management for the new single-plate switch. However, the new switch is metal, but the earth terminal on it too small to feed in the SIX 1.5mm earth wires I’ll have! So here are my questions:

1. Could I put each fitting’s trio of earth wires into one side of a single chock-block, and then lead a wire from the other side of that block to the earth terminal on the switch plate? ie I’d ultimately have just two wires going to the switch’s terminal, one from each block.

2. Should I put a ‘fly wire’ from the metal switch plate’s earth terminal to the earth terminal on the new metal back-box?

3. If the answer to ‘1’ above is “yes”, would it be better practice to put the three black wires for each gang into the port marked “LOOP” on my new switch? I kinda think having four chock-boxes floating around the back-box is, well, untidy at the very least!

Just for the record, it goes without saying that I will be turning off all power prior to changing the switch set-up. Thanks in anticipation for your help.

 

[EFLImpudence]

I feel comfortable to undertake a ‘cosmetic switch faceplate update’, but I want to make sure that I don’t breach any regs (or safety standards) in the change from two 1-gangs to one 2-gang set-up, so advice is appreciated.

Two-gang is just Two one-gangs next to each other.

The lounge in my 1987-build house still has its builder-original switch plates, which I want to update. Currently installed are two fittings: a ceiling light and a wall light, each being one-way. Each light fitting is switched on/off via a single gang (plastic) switch; the two switches sit adjacent to each other in a metal back-box that is sized/styled specifically for taking two, adjacent single switch plates. Each switch has three T&E cables into it – see this image:

Ok.

Two reds to two screwless ports marked “Common” and one red to the screwless port marked “1-way”; three blacks to one chock-block (left loose in the back box);

Those are the Neutral conductors. Not left loose; connected together.

three bare earths (sleeved) to the earthing terminal on the backbox. There is one earth terminal on each side of the back box to serve each of the switches.

Not really - they will both be connected to the back box and therefore each other so all the earth conductors will be connected to the back box and each other.

I intend to have both lights still independently switched on/off (1-way), but want to swap the existing set-up to a single switch with 2 rockers.

Not a single switch with two rockers but two independent completely separate switches.

I will take out the old back-box and make good as necessary, and fit a deeper (35mm) back-box to aid wire management for the new single-plate switch. However, the new switch is metal, but the earth terminal on it too small to feed in the SIX 1.5mm earth wires I’ll have! So here are my questions:

1. Could I put each fitting’s trio of earth wires into one side of a single chock-block, and then lead a wire from the other side of that block to the earth terminal on the switch plate? ie I’d ultimately have just two wires going to the switch’s terminal, one from each block.

Yes that would be fine as long as they are all connected together and to the switch.

2. Should I put a ‘fly wire’ from the metal switch plate’s earth terminal to the earth terminal on the new metal back-box?

May as well.

3. If the answer to ‘1’ above is “yes”, would it be better practice to put the three black wires for each gang into the port marked “LOOP” on my new switch? I kinda think having four chock-boxes floating around the back-box is, well, untidy at the very least!

Question 1 was about the earth wires; nothing to do with the black neutrals.

If the "LOOP" terminal on the switch is for 'parking' the neutral wires you can put each group of three in the respective switch's loop - just in case they are separate circuits although that is not likely.

 

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Thank you EFLI - very helpful and I can now proceed.

Re:

Those are the Neutral conductors. Not left loose; connected together.

Sorry... I meant it's the chock-block that's 'loose' in the back-box, not the individual wires (which are all attached to said block)

Re:

Not a single switch with two rockers but two independent completely separate swswitches

Understand. I meant single switch 'plate' (with two rocker switches).

Sorry if my terminology confused the question, but thank you for clarifying, and giving me the detailed answer I was looking for. AtB

 

[SUNRAY]

It looks to me that the position of the cables entering the 2 sides are just close enough together to fit in a single backbox and therefore be within the 'safe zone' created by the switch. Excuse my attempt to show the result.

However too wide apart to fit the regular knock-outs, so you may need to either make alternative holes in the new box or remove plaster above the switch to bring them closer together.

once the new box is in, the existing 2 bunches of cables will simply go to each switch exactly as before. One bunch of 3 earths would sensibly go to the back box and the other bunch of 3 go to the new metal switchplate.


If you are really lucky, while removing the box you may find something like this where 2 of the 6 cables are a link between the 2 boxes (shown as black) and/or the rest are run close together.

in which case the link T&E would be removed and a small piece of red linked across the switches, not the best example but like this highlighted yellow

Please mark the 2 switch wires (those in L1) indelibly with marker pen/tippex/paint etc on the red wire and/or the cable sheath while you know what's what.

 

[Adam_151]

Be aware that there is a chance the two switches could be on different circuits - As that is about the only logic I can come up with for it being done like this in the first place, why two separate cirucits, I don't know but you need to be aware its a possibility before you rush in, having only partially isolated it!

 

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Good thinking! I actually haven't tried isolating them individually at the Fusebox; I simply shut everything off with the master when I did the inspection/photo. There are other 2-gang switches in the house so, as you say, "why" would these two be apparently illogically separate.

 

[securespark]

My guess would be they are on separate circuits. But if not, it could be either something as simple as the spark ran out of 2 gang switches on the van. Or, it was designed that way.

If you know anyone with the same house as yours on your estate, see if their switch arrangement is the same.

 

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My guess would be they are on separate circuits....

If you know anyone with the same house as yours on your estate, see if their switch arrangement is the same.

Yes, my set-up is similar to other houses of this architectural design on this 1987 development. (I've yet to test if they're on separate circuits...)

 

[ebee]

It may well be that the initial designer/installer had a belief/desire to keep two switches of different circuits seperate thereby enhancing safety of those plunging fingers inside the switches
. Whilst making sure both earths were connected together, which is no bad thing.

So if you wire up each switch as they are now but as 2 gang 1 way configuration then ok.

If you dont like using strip connectors or "wagos" ok use a parking terminal on the switch.

Make sure that the earths all end up connected together by connectors/terminals and include both any metal faceplate on the switch and the backbox, just make sure that the connections are durable and resilient..

Make sure that the cables remain in the "zones of protection" on the completed job.
This might be acheived by a little bend as they approach the new hole positions (dont forget the grommets).

 

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Make sure that the cables remain in the "zones of protection" on the completed job.
This might be acheived by a little bend as they approach the new hole positions (dont forget the grommets).

Thanks ebee. By "zones of protection", I assume you mean the respective cabling groups 'stay away' from each other when the new switch plate is pushed back into the wall/back-box? (This is why I'm planning to deepen the cavity for a 35mm back-box.)

 

[ebee]

A "zone of protection" known as a permitted zone is really about cables hidden from view (sink in plaster for example).
In theory, if everybody keeps hidden cables in walls (less than 50mm deep) in certain zones then everybody else knows where they might reasonably be expected to be and therefore not accidentally nail thru/drill thru them etc.
so if we look at say a socket or a switch for example we might reasonably expect that a cable might be buried anywhere directly above to the ceiling or below to the floor or to the left or to the right of it. Also the corners of two walls within 150mm of each other or similarly on a wall within 150mm of the ceiling.
Similarly the same siting to a consumer unit.
It is generally accepted that this applies to a fixed appliance such as an electric shower etc.

 

[ebee]

Note - unlike a permitted zone at the top of a wall just below the ceiling there is not a similar zone near the floor so behind skirting boards is a big no.
With the ceiling one it also means if you are putting cornice on the wall/ceiling then the common practice of lightly pinning it in place whilst the adhesive sets could mean you pierce a hidden cable.

Note - relatively recently (a few years ago) another permitted zone was added that means a wall less than 100mm thick was considered to allow the permitted zones extend to the opposite side of the wall (in another room) providing it was easy to establish by means of door etc on that wall. Because it could not be 50mm deep from the surface of both sides of that wall.

 

[ebee]

Thanks ebee. By "zones of protection", I assume you mean the respective cabling groups 'stay away' from each other when the new switch plate is pushed back into the wall/back-box? (This is why I'm planning to deepen the cavity for a 35mm back-box.)

No that`s not what I was referring to.
Obviously you`d keep conductors apart if under strain and you`d keep conductors insulated where they touch lightly or where they might touch.