Creative light switch wiring

timhoward · Jul 28, 2022

I was working with a builder I know well today and he'd 2nd fixed some light switches.
All of them were spot on until I came to the switch either end of the kitchen to control the downlights.
My first reaction was "wrong switch - that's an intermediate - it won't work."
He said "Oh - I got it working!".

So I drew it out and had to concede this does actually function:

[ElectriciansForums.net] Creative light switch wiring

Then it hit me that all he'd done was essentially abbreviate this (as if there were a 3rd switch in one position):

I had to admit I'd never seen this one before and he in turn admitted it was totally trial and error on his part!
I thought I'd share this so anyone else who's led a completely sheltered life and not experienced this one wouldn't look as silly as I did.
(I changed the switch anyway, it requires too much thought left like that!)

Lucien Nunes · Jul 28, 2022

In the first drawing, there is no need for the junction of SL and grey to connect to L2. An intermediate is just two 2-way switches in one. The 2-way doing the work here is the one with L1 as common. The other 2-way that has L2 as common, is needlessly connecting the inactive strapper to SL. This has the minor disadvantage of increasing the capacitive leakage when off, as the strapper that would otherwise be floating is now connected. The 'Conversion 2-way' scheme where PL and SL are connected to the two strappers, also has this charactieristic, so this is more a theoretical objection.

Of course the builder could equally have put PL and SL in L3 and L4 and it would have worked just as well, in conversion 2-way form.

westward10 · Jul 28, 2022

An intermediate switch can be used for one way or two way switching.

timhoward · Jul 28, 2022

westward10 said:
An intermediate switch can be used for one way or two way switching.

It’s funny that I’ve just accepted the strappers are swapped over for all these years and never considered what was going on internally to do it….
It’s SO obvious now pointed out!

telectrix · Jul 28, 2022

we live and learn.i still finding somethng new at 75. my pertinent question is "is ther life after death, or is it just a con perpetrated by the church?"

Lucien Nunes · Jul 28, 2022

I raise you my own version of creative light switch wiring.

Supply loops-in and out via the switches.
Lights and switches are normal fittings.
All cables are SINGLE core.

This seemingly magical feat relies on combining two long-obsolete practices that you've probably never seen for real, but both did exist and perhaps someone used the two together as I have done.

Timbo · Jul 28, 2022

telectrix said:
we live and learn.i still finding somethng new at 75. my pertinent question is "is ther life after death, or is it just a con perpetrated by the church?"

Let us know when you peg it, Tel!

timhoward · Jul 28, 2022

Lucien Nunes said:
I raise you my own version of creative light switch wiring.

Supply loops-in and out via the switches.

Lights and switches are normal fittings.

All cables are SINGLE core.

This seemingly magical feat relies on combining two long-obsolete practices that you've probably never seen for real, but both did exist and perhaps someone used the two together as I have done.

Assuming that the horizontal length between the switches is connected to Neutral?
I think the polarity at the lamp would change dependant on which switch was in use.

Please educate me about the two practises, is one of them knob and tube wiring / carter system from USA?

littlespark · Jul 29, 2022

I came across this a year or two back. T&E feed to switch, then a 3C&E up to light, and down to far switch. I then recall there was loop feed out for another switch as the 3 core was carrying a perm live and neutral.

I had to check at the rose, and whoever had connected it had removed the sheath and only cut the red and cpc. The yellow and blue were intact.

timhoward · Jul 29, 2022

@littlesparks The only regs issue is switched neutral ‘sometimes’ I think?

littlespark · Jul 29, 2022

timhoward said:
@littlesparks The only regs issue is switched neutral ‘sometimes’ I think?

Yes. Was my thoughts at the time.

Wasn’t actually working on that particular circuit, But had to have a look for myself.

Lucien Nunes · Jul 29, 2022

Yes one of the tricks here is Carter switching, where each 2-way sends either L or N to one side of the lamp. I think the NEC prohibited it as early as the mid 1920s, the main objection being that in one of the off permutations, both sides of the lamp are live, especially dodgy with ES lamp-holders.

But what about my single-core cables? How do both line and neutral get to all the switches?

timhoward · Jul 29, 2022

Lucien Nunes said:
But what about my single-core cables? How do both line and neutral get to all the switches?

Was the whole circuit in series?!

Lucien Nunes · Jul 29, 2022

No.

Blah blah blah, my postilion has been struck by lightning

timhoward · Jul 29, 2022

Lucien Nunes said:
No.

Blah blah blah, my postilion has been struck by lightning

Maybe I stand more chance if you can reveal whether this is a single phase system and which country you were in at the time?!

Creative light switch wiring

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