Two Way Lighting - Which way to do it?

[pete01]

I think it used to be a common way of wiring the 2-way switching of the landing light.

Yeah its actually how it's done in my own house with red and black sheathed singles, but I've never done it myself.

 

[GreyBana]

Thanks ebee! That's helpful. I actually don't mind the sound of "second option version b", keeps all the connections in one central place, so it would make my addition of the Zigbee relay very easy!

 

[SUNRAY]

I did come across one case where someone had missunderstood their electrician friends advice and did not use twin and earth on either switch on a two way switch circuit but instead run a 3C & E from the rose to switch 1 and also a 3C & E from rose to switch 2.
My intial gut reaction was to think "No that`s wrong!" yet I soon realised no it was not wrong and could indeed it would work that way but you would need an extra choc block/crimp/wago in the rose and slight alterations to the rose connections yet only one 3 core to each switch and no T & E to either .
So if anybody actually does that way should we nominate that as say " 2nd option version B" and classify the one you`ve already mentioned as version A ?

And guess where that additional terminal often ends up...



Here's an example from 17 years ago:

It was before the earth wiring in the harmonised cables were installed and not very clear so I've added some pink clues

 

[endecotp]

One benefit of the 3 core (& E) cable between the two switches method is if anyone has an Induction loop hearing aid it used to be a lot less chance of imparing usage of that hearing aid

This is an issue in some cases, but I don’t think it applies to any of the circuits described in this thread.

 

[ebee]

This is an issue in some cases, but I don’t think it applies to any of the circuits described in this thread.

Yes you are probably correct - I added that observation for a bit of completeness to the item I wrote as well as the mention of the 2nd option version B" I had seen and initially debated with myself.

The hearing loop problem (if it still exists with modern hearing aid techology - or interference on any other electronic gadgets ( would be reduced greatly, maybe vanish completely) if a loop say with single cables on differing routes than with closely parallel conductors within multicore cables such as T & E or 3C & E etc.

So I considered still worthy of a mention even if, in this case, not greatly likley - it`s a topology worth avoiding sometimes. In a "Every Little Helps" sort of idea!

 

[davelx]

The first method was standard for wiring the 2-way switching for stair/landing lights in older housing stock (1930's housing boom) when there was only one lighting circuit, no RCDs and the lighting wiring was singles in split conduit with no earth. The live feed for the landing light was taken from the ground floor lighting to the common of the downstairs switch, then just 2 conductors needed to be run to the switch on the upstairs landing, The common from that went to the landing light, and the neutral from the light was tapped into the neutral at one of the other upstairs light fitting (or often a junction box).

Later, some such houses would have been rewired (pre RCDs) with separate lighting circuits upstairs and down, and no one would have realised that there was now a "borrowed" neutral, i.e. the live feed for the landing lights came from the ground floor lighting circuit, but the neutral was from the first floor lighting circuit. This was not ideal but still worked -- until we rewired with separate lighting circuits up and down and RCDs in CU's, when the borrowed neutrals suddenly became a problem.

The more modern way of wiring for n-way switching avoids this issue, and just happens to be better from an EMC perspective. I also think it's neater and easier to trouble shoot when necessary.

 

[ebee]

Yes, and in my experience around this part of the UK it was still common to require houses (particularly council houses) well into the 70s in T & E (and some S & E) with two lighting circuits yest the borrowed N still put in, usually via stairs lighting.
So old or new it still existed well into the RCD popularity period and then problems started to arrive (if you do not consider risk of shock via borrowed N when working on a "fully disconnected" lighting circuit - I think actual problems with shocks that way were a lot less than the potential for such actually happening therefore not as noticable throughout the electrical community and add that with the fact that not all electric shocks actually ends with electrocuion hence not as noticeable - not sure how many broken limbs etc actually resulted from such "OUCHs " either but I guess the odd one or two. LOL.

 

[333rocky333]

There's also an alternative version of the second drawing, by using 3 core and e from the rose to the switch and 4 core and e between the two switches, you can have a Neutral at each switch
Then you have the means to supply a light direct from either switch or fit fancy switches that require a Neutral

 

[pete01]

Or take s 3 core from the light to each switch and do the connections at the light.

 

[ebee]

Or take s 3 core from the light to each switch and do the connections at the light.

If I got you right on that one Pete isn`t tht the one I called version B ?

There's also an alternative version of the second drawing, by using 3 core and e from the rose to the switch and 4 core and e between the two switches, you can have a Neutral at each switch
Then you have the means to supply a light direct from either switch or fit fancy switches that require a Neutral

There's also an alternative version of the second drawing, by using 3 core and e from the rose to the switch and 4 core and e between the two switches, you can have a Neutral at each switch
Then you have the means to supply a light direct from either switch or fit fancy switches that require a Neutral

Yes correct but is 4 core & E readily available as such?
Single, Single & E, T & E or 3C & E are pretty common ad readily available but 4 core isnt? unless you using 5 core lex equiv to 4 cores plus an E conductor or 5 cores of SWA
Unless I missunderstand you.

 

[morqthana]

Later, some such houses would have been rewired (pre RCDs) with separate lighting circuits upstairs and down, and no one would have realised that there was now a "borrowed" neutral, i.e. the live feed for the landing lights came from the ground floor lighting circuit, but the neutral was from the first floor lighting circuit.

Until very sudden realisation arrived one day in the form of an "Ow, f*%$" when working on one of the circuits after turning it off at the CU.

 

[pete01]

If I got you right on that one Pete isn`t tht the one I called version B ?

Err not sure, I think you meant a 3 core between switches, I meant a 3 core from the light twice so you end up with 1x 3 core at each switch.

 

[333rocky333]

Yes correct but is 4 core & E readily available as such?

Thinking about it proberly not, it was long ago I did it and i may have used 2.5mm it was flat like twin and earth i assume it was used for 3 phase and neutral from a job somewhere

 

[securespark]

The first way seems a bit more awkward to me, I think it was done more years ago when they used to use sheathed single cables.

I've never done it in a house, only when wiring in conduit.

It was often done in houses where there would be switches near the bottom of the stairs for the hall and landing lights and one near the top of the stairs for the landing light.

So you'd tap the live feed off the hall switch for the landing switch common downstairs, run a T&E up to the landing for the strappers then run a single with sheath from the common upstairs to the landing lamp.

And that, mon ami, is where you get the famous borrowed neutral scenario from.

Edit: Apologies...I'm very late to the borrowed neutral party...

 

[ebee]

Yes pretty much the stairs is the culprit for borrowed N scenario.
I have seen a very few on others but only a very few.
I did see one with a "Borrowed L" if you want to call it that.
Bathroom of a large house (Two fairly large terraced houses knocke thru into one actually).
The light in the bathroom was on the lighting circuit.
ditto the extractor fan but the timed overun perm L was straight from the ring final (not even fused down) .

Also in that installation a seperate CU for the electric shower - no idea how, installtion E conductor omitted to that CU (unless someone had later taken it out and just left the tails there of course, however unlikely!) but it had a recent PIR (EICR) and a figure for Ze for that consumer unit which tallied with the reading I took on that consumer unit earth bar no other ciruits present.
Therefore the only earth polarity on that shower was from pipework or any accidental supplementary bonding>
Another "Little Gem" was a fault recorded on the immersion heater circuit was - 6.0 T&E cable, 32A MCB to the first immersion heater 3KW standard and a short run from the 1st heater to second heater in 2.5 T & E defected as Code 1 "Not Allowed". Whether they awarded that code and comment because because they disliked the thought of a 2,5 spur to the second heater or because they thought 2 x 3KW loads on one 32A circuit too much I could not guess!