3 way switching query

[pctree]

I would appreciate some advice regarding 3 way light switching. I have studied the wiki and understand the method shown, but I was wondering if an alternative was feasible.


My garage has 2 way switching at present, with a switch at each end, both close to a corner. I would like to add an intermediate switch halfway down the length of the garage, on the opposite wall. The routing of the current 3 core + Earth cable would mean that simply rearranging the cable to connect one existing switch to the new intermediate, then using a new length of cable from the intermediate to the other existing switch would be problematic, and I would therefore prefer to use two (fully exposed) junction boxes, splitting the existing cable.


I see from the wiki that the cable linking the Common terminal of the 2 way switches (the yellow cable in my case) is joined in the intermediate switch, bypassing the terminals. As I would be running two new lengths of cable across the garage from adjacent junction boxes, I was wondering if I would be able to merely run a short length of cable between the junction boxes to the relevant (yellow cable) terminals, then use 2 core + earth for the remainder of the JB to intermediate switch wiring? And if so, would I be OK in snipping back the black cable and using the red and earth only in the cable joining the two JBs? Or should I use a choc block/Wago to terminate? And am I OK to use non-harmonized colour 1mm cable, which I already have?


Hope I have explained this properly, and I would be more than happy to be told there is a better way!

 

[ban-all-sheds]

A drawing of your proposed solution would be easier to follow.....

Yes, you can use the cable you have.

 

[EFLImpudence]

You can interrupt the cable between the present switches anywhere you want - with a four-core cable to the new switch.

 

[PBC_1966]

So long as you can cut the existing cable and there's enough slack to reterminate, you could just use a single 6-way junction box to make the connections:

https://www.tlc-direct.co.uk/Products/BG606.html

Two terminals to extent one pair of travelers out to the new switch, two terminals for the second pair, one terminal for the common connection passing straight through, and one terminal for the earths.

 

[pctree]

Many thanks for the replies. If I can find enough slack, PBC_1966's suggestion would be excellent - hadn't thought of that! But in case I can't - very rough diagram below:

Intermediate switch wiring would be as in the wiki, but with red and black instead of red and blue at the 4 terminals.

 

[PBC_1966]

Many thanks for the replies. If I can find enough slack, PBC_1966's suggestion would be excellent - hadn't thought of that!

One other trick which you can use with the traditional round British junction boxes: You can cut the sheath of the existing cable back without cutting the whole cable, and run one or more conductors straight through the box uncut, e.g. your common wire in this case. Or you can also carefully remove some insulation (if applicable) and pass the uncut wire through a terminal to tap off to another cable, since the terminal screws can be completely removed for the operation.

So with something like the 6-way box pictured, you can run the common straight through, drop the earth into one of the central terminals so you can connect your new earths to it, and cut the other two conductors midway to split them off to the four "outside" terminals in the box for connection to your new wiring.

 

[pctree]

Fantastic - great advice, very many thanks!

 

[Risteard]

Many thanks for the replies. If I can find enough slack, PBC_1966's suggestion would be excellent - hadn't thought of that!

One other trick which you can use with the traditional round British junction boxes: You can cut the sheath of the existing cable back without cutting the whole cable, and run one or more conductors straight through the box uncut, e.g. your common wire in this case. Or you can also carefully remove some insulation (if applicable) and pass the uncut wire through a terminal to tap off to another cable, since the terminal screws can be completely removed for the operation.

So with something like the 6-way box pictured, you can run the common straight through, drop the earth into one of the central terminals so you can connect your new earths to it, and cut the other two conductors midway to split them off to the four "outside" terminals in the box for connection to your new wiring.

The problem with that approach is that the cpc will not be sleeved/identified.

 

[PBC_1966]

The problem with that approach is that the cpc will not be sleeved/identified.

No big deal, but if it bothers you that much you can wrap a couple of turns of green/yellow tape around it either side of the section which is to go in the terminal.

 

[Echo the husky]

It's usually possible to cut the cpc for sleeving and still have enough slack to connect it into a terminal. It used to be quite common to hide the unsleeved contiunous cpc at the bottom of the JB with the other sleeved cpcs on top.

 

[PBC_1966]

It's usually possible to cut the cpc for sleeving and still have enough slack to connect it into a terminal..

That's ture - After all, you only need to gain about half an inch.

 

[Risteard]

The problem with that approach is that the cpc will not be sleeved/identified.

No big deal

But not permitted.