Wiring 2 gang switch with one 3-core cable

[jhs14]

Hi all

I have a single 1 way light switch fed from the ceiling via chased metal conduit (presumably original to the house 1950s). I want to add a second 1 way switch (for a new light) to make the switch 2 gang.

The conduit is on the narrow side and I wonder if I'll have difficulty feeding two T&Es down to the switch. Is there any reason why I can't use a single 3-core cable, using one core as the permanent live for both switches (split via terminal block behind the switch), and the other two as the switched lives for each switch? (all sleeved appropriately)

I await an obvious reason why this wouldn't work!

Thanks,

 

[OwainDIYer]

Where are you running your neutrals? Lives and neutrals should be run together in the same cable/conduit.

You don't have to use T&E in conduit, you can use singles or strip the sheathing off T&E. You don't need to use terminal strip to split the live, just run the live into one switch terminal and a short length of linking wire to the second switch terminal.

 

[jhs14]

Where are you running your neutrals? Lives and neutrals should be run together in the same cable/conduit.

Presumably it's no different to using a T&E for a single switch (live/switched live - no neutral)?

Neutral will be looped at the rose (or more likely an MF JB under the floorboards of room above)

You don't have to use T&E in conduit, you can use singles or strip the sheathing off T&E.

I'm imagining this conduit will be a bit sharp and rusty (as others in the house have been) so I don't fancy dragging cores from T&E down there with no outside protection..

 

[EFLImpudence]

(split via terminal block behind the switch)

Don't do that - just put the wire in the switch terminal with another short wire to the other switch.

 

[sparkwright]

Where are you running your neutrals? Lives and neutrals should be run together in the same cable/conduit.

You don't have to use T&E in conduit, you can use singles or strip the sheathing off T&E. You don't need to use terminal strip to split the live, just run the live into one switch terminal and a short length of linking wire to the second switch terminal.

I don't think much of any of the above comments.

Most lighting circuits will not have the live and neutral constantly within the same cable or conduit.

If this was the case, full conduit systems wouldn't be wired the way they traditionally are, and single+earth and single PVC PVC cables wouldn't exist.

The metal conduit in the wall sounds like it is just a switch drop run only, designed for sheathed cables, so running unsheathed wires down it is pretty rough, and no doubt the conduit isn't earthed either.

If the conduit in question was part of a full conduit system then unsheathed singles would have been used throughout. It doesn't sound like this is the case here.

Two T+Es or one 3 core+E are very likely to fit down your conduit.

I suspect two T+Es would save too much alteration to the wiring.

 

[PBC_1966]

Is there any reason why I can't use a single 3-core cable, using one core as the permanent live for both switches (split via terminal block behind the switch), and the other two as the switched lives for each switch? (all sleeved appropriately),

None at all - It's done regularly. Obviously the two lights will be on the same circuit with the common feed, and you need to make sure that you pick up the neutral from that same circuit for the new light (not a "borrowed" neutral from a different circuit).

Where are you running your neutrals? Lives and neutrals should be run together in the same cable/conduit.

Why? If you're thinking about the possible induction of currents in the conduit (or to anything else in the outside world), remember that in a switch loop the current in each leg is in opposite directions at any given instant and thus cancels out just as if it were live & neutral inside. That holds true for a simple 2-core switch loop or for a 3-core for a 2-gang switch.

 

[ban-all-sheds]

Two T+Es or one 3 core+E are very likely to fit down your conduit.

Well - I have to assume that you've done it more than I have, but having in the past tried to get new cables down rusty old 1950s slip conduit, I would never be confident of success.

 

[phatboy]

I have a 1950's house, and the conduit won't take 2x T+E's thats for sure. It would however take a 3+E cable, which seems like the best solution to be. You would probably need to terminate into a junction box (Maybe maintenance free) above the cable run to split the circuit back out.

This seems like the simplest and most elegant solution, without going to the extent of chasing the wall....

 

[sparkwright]

Well - I have to assume that you've done it more than I have, but having in the past tried to get new cables down rusty old 1950s slip conduit, I would never be confident of success.

Yes, I'm sure I've got those cables down slip conduit before.

I'm sure I got two T+Es down one tube for two back to back switches - one 1-way and one 2-way, with a junction box above.

It would have been 1.0 mm2 though.

I pulled out a length of slip tube only yesterday - had I known I would have saved it and experimented.

Don't know if the size varied at all.

Getting a T+E AND a 3 core+E down one has proved impossible though.

I'll see if I can find a piece of slip tube. Isn't it roughly the same as a piece of (15mm?) copper pipe?

EDIT. I think slip tube is smaller than 15mm copper pipe.

 

[Iggifer]

Yea slip tube is tiny. I pulled some out last week. Surprisingly strong for how small it is, but I reckon it's in-between 10mm and 15mm.

I would wager, it's 12.7mm either ID or OD, which is 1/2" by my calculations. Would seem logical.

Might be taking more out on Monday, if I remember I'll have a look.

 

[JohnD]

some slip tube has a folded seam, and splits open if you try to bend it. I think there was 1/2" and 3/4"

 

[ban-all-sheds]

That was what I had. Didn't measure the size, but if I had there would have been 2 dimensions to quote, as it was oval, not round.

 

[phatboy]

If needed, I can get the dimensions of a length that I removed from a wall the other night?