Intermediate sw wiring/neutral at sw

[Kuba]

Hi all,

I was watching Adrian Daveys video on YouTube and he had this diagram drawn on the board. Made me think of a scenario I came across before when I had to second fix a flat with similar light circuit and the difference was I had a s/l with a feed at the first switch.
Looking at the diagram above, I understand that the grey was used as neutral to provide continuity between s/l and supply to form a circuit and then brown from s/l is your common. That’s clever and if I was first fixing a flat that’s how I would probably wire it. You have your neutrals at each point in the circuit to satisfy the regs recommendation too.
So what if you come across my scenario, you have a 3core, feed and a s/l at first switch? With blacks linked at intermediate sw and from each common, feed at L1 and s/l at L2 with their respective strappers, everything will work how it should but both intermediate and last switch won’t have neutrals.
Would you say it’s fine or come up with a different solution? I’m not a sure if I missed something but just wanted to clarify this in my mind. Is this a mistake/lack of experience on the first fixer’s side or just the norm?
Thanks

 

[Lister1987]

View attachment 63384

Hi all,

I was watching Adrian Daveys video on YouTube and he had this diagram drawn on the board. Made me think of a scenario I came across before when I had to second fix a flat with similar light circuit and the difference was I had a s/l with a feed at the first switch.
Looking at the diagram above, I understand that the grey was used as neutral to provide continuity between s/l and supply to form a circuit and then brown from s/l is your common. That’s clever and if I was first fixing a flat that’s how I would probably wire it. You have your neutrals at each point in the circuit to satisfy the regs recommendation too.
So what if you come across my scenario, you have a 3core, feed and a s/l at first switch? With blacks linked at intermediate sw and from each common, feed at L1 and s/l at L2 with their respective strappers, everything will work how it should but both intermediate and last switch won’t have neutrals.
Would you say it’s fine or come up with a different solution? I’m not a sure if I missed something but just wanted to clarify this in my mind. Is this a mistake/lack of experience on the first fixer’s side or just the norm?
Thanks

Draw it out and show what you're explaining.

 

[Kuba]

Draw it out and show what you're explaining.

Cpcs omitted, and as you can tell neutrals would have been joined at the first switch, no neutrals elsewhere in the circuit.

 

[telectrix]

to provide a N at each switch you'd need a 4 core strapper cable instead of 3 core, unless you are using the old method whereby the L is fed to common of one 2way switch and the S/L from the common of the other 2 way switch, using 2 of the 3core as strappers and the spare core fot N.

 

[Kuba]

to provide a N at each switch you'd need a 4 core strapper cable instead of 3 core, unless you are using the old method whereby the L is fed to common of one 2way switch and the S/L from the common of the other 2 way switch, using 2 of the 3core as strappers and the spare core fot N.

When you say 4 core do you mean 3 core and earth? And 3 core as twin and earth? ? sorry if I’m asking a stupid question but I haven’t heard of a cable with three strappers and tried googling it.
The drawing I made above has 3 core and earth at first switch, feed and s/l, two 3 core and earth at intermediate and one 3 core and earth at second switch.
I still can’t see how you can wire it and still provide a neutral at every switch.

 

[telectrix]

no. - 4 core would be 4 live conductors + earth. this can't be found in "normal" domestic cable. you' could use 5 core flex ot 3 core/E + a separate single sheathe cable to provide the extra conductor.

 

[Kuba]

no. - 4 core would be 4 live conductors + earth. this can't be found in "normal" domestic cable. you' could use 5 core flex ot 3 core/E + a separate single sheathe cable to provide the extra conductor.
View attachment 63420

I thought so ? therefore in the ‘real world’ would people just not bother about neutrals in every switch or wire it the old method way? Using flex seems like an odd choice and using single core blue cable would be okay if it was in conduit? Scenario I mentioned was in a new built block of flats. Switch line could have been easily been pulled to the last switch instead of where the feed was by whoever was doing it on price.
Thanks for clarifying btw ✌?

 

[telectrix]

sheathed single can be run just same as T/E. no need for conduit. that's only for unsheathed singles.

 

[Lucien Nunes]

However you cable it, if you want line and neutral to be available at all switch positions with only the cables between the switches looping through (i.e. not also looping at the lights) you need four live cores in the cable between the 2-ways. If there is an intermediate, it has to be done as in your first pic, using 'conventional' 2-way, so that the four cores are PL, N, and strappers L1 and L2. Your second pic showing 'conversion' 2-way works equally well for just 2-way, the cores become L1(=PL), L2(=SL), com and N. But it falls down with an intermediate, because that swaps L1 and L2 so you can't pick up a PL at the far switch, because it could be either wire.

To get the four live cores, you could run it as two T+E cables (advantage: already on the van), a 3C+E plus one sheathed single, or 4C+E which is neatest but not available as 624x cable (i.e. flat cables from the T+E family.) But 4C+E is available in BS8436 cables (e.g. Flexishield), FP and SWA. So in most common sheathed wiring systems other than 624x flat cable it can be done with one cable.