Anybody ever come across this?

[hightower]

Anybody ever come across this? Basically, 2-way lighting (old hence old colours). 3-core goes to both switches and that is the only cable to enter the switches. The 3-core runs to a junction box - the blue and red are straight through (uncut), the yellow is cut, one end wired to the supply, the other end wired to the light. The return from the light is then wired straight in to the supply neutral.



This is a currently working circuit I came across yesterday - I can see how it works etc, I was just wondering if others have come across wiring like this before and why it would be done like this? In this example I came across it on a landing light with upstairs/downstairs switching.

The back boxes were shallow, so I wonder if it was done this way to limit cables entering the boxes in limited space? Is something like this fairly common practice?

 

[Darkwood]

Plenty of times, wired it a few too, its an easy way to turn a existing 1way into a 2 way by running a 3core from the existing switch to new switch.

 

[hightower]

Yeah, the more I look at it the more I think "that's pretty good actually". Where would the junction box typically be installed for a landing light? Under the landing light floor, or in the attic? (I didn't get chance to check the attic yesterday - I just came across it and it made me curious - I actually took a stab at the junction box drawing above as that's the only way possible I could see it working)

 

[assegayer]

why do all of that when you can just run a three core from the one way switch, making it a 2 way light

 

[hightower]

why do all of that when you can just run a three core from the one way switch, making it a 2 way light

Good point. The only thing I can think of would be if it used to be a 1-way, it got converted to a 2-way but there wasn't a lot of room in the conduit so they pulled the 3-core through while pulling the 2-core out? (a 2 AND a 3 would take up a lot more space)

Like I say, I haven't seen the junction box, I just assume that's how it's wired as I can't see any other way it would work. It has truly piqued my interest lol.

There's 2 switches, each only have a 3-core cable (no 2-core in sight), but the light fitting only has a 2 core switch. The switches power nothing else but this light. Can anybody see another way it would work?

 

[Richard Burns]

You have shown the conversion to 2 wire two way switching, but you can also do three wire two way switching in a similar manner.
The diagram below shows the method you have described at the top, the second diagram is conventional three wire switching, but the arrowed connections can actually be made at any point along the two cores between switches (the obvious default case is to connect the line and Switch line at the other switch's L1 and L2).
This is shown in the last diagram.

This is another possibility for the arrangement you describe.

 

[hightower]

Thanks for your help with this guys. Actually used this to wire two lights that had limited switch space today while working with my uncle. Love this place, some very helpful people (and some not but that's a different discussion)

 

[rich.250]

We do similar to this on rewires but just take the 3core straight to the pendant!

 

[hightower]

Mind taking a photo sometime and sharing it? Be interesting to see

 

[rich.250]

I will when I return there, I was explaining it to my apprentice. It's exactly the same just take out the cable to the light.