Creative light switch wiring

[timhoward]

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:

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]

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]

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

 

[timhoward]

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]

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]

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]

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]

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]

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]

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

 

[littlespark]

@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]

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]

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]

No.

Blah blah blah, my postilion has been struck by lightning

 

[timhoward]

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?!

 

[Pretty Mouth]

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

Singles? Could it be that the circuit is using earthed conduit as a neutral?

 

[littlespark]

is the lines marked "supply" and "loop" just singles? How can you have a line and neutral if theres not one supplying? Unless Prettymouth is right and the conduit is being used as return path.

 

[Lucien Nunes]

Conduit possibly, but I actually had in mind a metallic-sheathed cable such as Stannos, which was used and recommended for earthed-concentric wiring. This was true TN-C where there is no separate earth and neutral anywhere, just a combined PEN via the sheath. It was a requirement that all fittings had threaded spouts, into which special bushes were screwed with the sheath soldered in. So every fitting was earthed and neutral connections were made to flyleads from the bushes, much like an MI earth-tail seal. It was very compact, a light could be fed from a cable around 4mm diameter overall.

 

[littlespark]

i kinda knew it wasnt going to be something straightforward.

 

[freddo]

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've seen similar lighting wiring with supply cables looped at the switch connected as below, with the neutrals joined in the 2 way terminal. This worked fine for a few months but failed after it started flashing over and would sometimes trip the MCB when the light was switched off. The switch soon failed after the tripping started. The customer had replaced a Hager light switch with the built in neutral loop terminal with a normal (cheap) switch.