What is the middle switch doing?

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Hi all, I have a new question for you :)

We're looking to replace our old outside front lights with PIR ones. Tonight I wanted to check the wiring behind the light switch to see what we're dealing with. And I'm a tad confused hence this post.

The light switch in question is a 3-gang.
  • The leftmost switch is a 2-way switch operating the living room lights (it has an 'opposite' 2-way switch at the other side of the room).
  • The rightmost switch operates a porch light and two outside lights. (The two we're looking to replace with PIRs). With this switch on, all three lights come on of course.
  • The middle switch... has never seemed to do anything.

So, this is what we get with the front cover off (it's an unusual design of switch, I'd be interested to know how old roughly it is):
upload_2019-10-14_18-9-50.png



And with the next bit off, we get the interesting stuff:
upload_2019-10-14_18-10-41.png


Now just in case it's not clear from the above, the middle switch has nothing connected at the bottom, just the two red wires connected in the top.
There is also a black wire just cut short, visible (just) between the two red wires at the green wire, further back where it comes in from the wall.

You can probably guess my question, but... what is the middle switch doing, as it is simply connected at the COM terminal, to the rightmost switch?

In other words, why isn't the red wire from the cable going directly into the rightmost switch instead?


Also, is any of this going to cause us problems for fitting our PIR lights? (They will be running off the rightmost switch, which consequently will have to be switched on all the time of course).


This is my first 'experience' with a 3-gang switch and because the middle one wasn't working I expected it to have an old rubber wire connected somewhere or somesuch... but not this.
 
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As you said, the middle switch is not doing anything else than pass permanent live to the other switch.
Yes, a longer bit of wire would bypass this "joint" at the middle switch and feed directly the other one.
But you can leave it like that if you want.
Before you close everything, make sure no copper is exposed and everything is screwed properly.
 
What it used to do is obviously impossible to say.

To find out you will need to determine where the two reds in the wire nut and and the cut black go.
 
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Thanks all... underground bunker haha could be :LOL:

So it is all safe enough, as it stands, to wire the PIR lights in? That's my priority of course, to make sure we can safely put the new lights up.

Then when we have more time (so many jobs on the go, so little time) I'd love to start figuring out where the cables go.



It's got me wondering now (and obviously none of us can know at this point so I'm not expecting answers!) but when we first bought the house, the light switch at the other side of the living room also used to be a 3-gang (a normal square one though) and there was an outside light at the rear which worked. But when the house was rewired shortly after, this switch changed to a 2-gang and they moved the third switch into the rear hall as a new switch... I think because there was old rubber wiring to the third switch.

And we often think that perhaps when they did that, they inadvertently cut off the rear outside light. :mad:

Which long meandering rambling leads me to the 3-gang switch as per the subject of this thread... I'm now wondering whether the middle switch possibly also used to operate the rear hall / rear outside light in a 2-way fashion and perhaps the leccies disconnected that end as well (not that they explained any of this to us).

Just a thought.

Unfortunately we didn't take enough notice of what-did-what before the rewire so we don't know for certain.

I need to get my head around how wires are traced (other than pulling up floorboards) as that's something I'm quite unfamiliar with, continuity and all that. Which I guess is what's needed here.
 
A multimeter and a 9 volt battery do wonders.
In most applications you can trace where the wires go by just checking continuity and flipping switches and mcb/rcb.
 
MK Gridswitch, pre-Logic Plus so before about 1997. Green earth sleeving before 1977.

How cheap a job is that though, not even using grommets? And I don't like the look of the earths - are they wedged under a bent lug?
 
A multimeter and a 9 volt battery do wonders.
In most applications you can trace where the wires go by just checking continuity and flipping switches and mcb/rcb.

We have a multimeter :) I just can't get my head around sticking one probe at one switch and stretching to touch the other probe at another switch across the room... that can't be right, can it?



MK Gridswitch, pre-Logic Plus so before about 1997. Green earth sleeving before 1977.

How cheap a job is that though, not even using grommets? And I don't like the look of the earths - are they wedged under a bent lug?

Thanks for the info... surprising the switch could be that new! (I was hoping it was something really old).

I think (leccy's back on now so I can't look!) the earths are connected to a terminal at the top of the box... the photo doesn't really show that, sorry.

Do you think it doesn't look safe enough? (Still worried about the PIRs).
 
Thanks for the info... surprising the switch could be that new! (I was hoping it was something really old).
Could easily be 1960s, that style of switch was available for a very long time.
Later ones (1990s) were compatible but had a flat switch rather than the design you have got.
 
Sorry to harp on, but anxiety is getting the better of me and for some reason I'm worrying about having this switch on all the time once the PIRs are connected.

Can you put my mind at rest that this switch will be ok for the PIR lights outside? It's worked fine whenever we've switched on the old outside lights, but its the fact of leaving this switch on all the time which is bothering me for reasons I can't explain.
 
Could easily be 1960s, that style of switch was available for a very long time.
Later ones (1990s) were compatible but had a flat switch rather than the design you have got.

The 1960's version was fixed to the grid with screws, so later than than..
 
Thanks all :LOL: mind duly put at rest, and I shall be sure to teach myself continuity testing.

And I've learned about MK grid switches too, so that's a bonus.
 

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