Strange Wiring to 2 Gang 2 Way Downstairs Switch Ask questions and find answers to many subjects relating to electrics and electrical work

[joniemaximus]

I've recently moved into an 80s built house and i have some questions about the wiring i've found.

I was looking at replacing the downstairs switch to the upstairs landing (2 gang, 2 way) for a white switch like for like. At this point id say the switches for this light work as expected and i'd assumed the left hand switch operated the upstairs light (it did) and the right hand switch was for a garage light that was no longer used as the garage had been converted and new lights added and the switches moved inside the new room (I'd also found what i thought was the remnants of that switch in a junction box in the loft of the converted room).



With new switch in hand, i isolated the supply to the switch, checked that i had, then removed the switch from the wall.



The wiring from the switches i found is as follows:

Landing light switch (Left hand switch):

Com: connected to red cable

L1: connected to blue cable

L2: connected to L1 of the right hand switch using single core grey cable



Mystery switch (Right hand switch):

Com: connected to single core grey cable

L1: connected to L2 of the left hand switch

L2 not connected


I thought L2 from the Landing light switch (Left hand switch) would terminate at the switch upstairs for the landing so i don't understand why it would go through the mystery switch first, but to make it worse i can find no combination where the mystery switch does anything. Why someone would do this i have no idea. However if this is the case i have no idea what is connected to the random junction box i found above the switch (albeit on the opposite side of the wall) which i assumed would go to this switch. There is no other electrics even close that would have been part of the pre-conversion build?.


Now i'm well aware i'm probably going to have to contact a competent person. Just wondering why anyone would do this or if someone could help me understand what is happening?

[Mr White]

To answer your question take a step back and read it as others will see it.
You are in effect asking why someone we do not know has done something you do not understand.

It is up to the individual how they choose to do it, if it complies or not is another question.

[joniemaximus]

I wasn't asking anyone to make judgement on the person that made the connections that way, I was trying to understand given other peoples vastly superior knowledge how this circuit might work. I like to understand what things are doing and what is happening.

[Mr White]

I realised what it was you were asking when I replied, as such my answer still stands.
"You are in effect asking why someone we do not know has done something you do not understand."

In plain English I am saying:

Only the person who wired it knows what they were doing and what colours they chose to do it.

Believe it or not there is no standard wiring or colour configuration for lighting other than Live is red and Neutral is Black or as it is now Live is Brown and Neutral is Blue. (Not counting 3 core and earth) If there was such a specific configuration it would be much easier for everyone, but alas there isn't.