# 2 way switch wiring with single core cable?

#### hvendlor

Trying to make sense of the lighting circuit upstairs.

Bottom of the stairs there's a 3 gang 2 way switch. One of the switches turns the landing light on.

Single 2 way switch on the landing, also turns the landing light on.

What I don't understand is that there's only 1 single core cable(live) between the light and the landing switch.

Then there's a twin and earth cable running from this switch to the switch at the bottom of the stairs.

I always thought you needed 3 core cable between switches for 2 way lighting?

thats the orthodox method, the three core method is called the conversion method. Unless you only have one lighting circuit there is every probability that your landing light takes a live feed from the downstairs lighting circuit and a neutral from the upstairs circuit, if working on the circuits make sure you isolate both circuits.

Quite normal. The feed probably comes from the downstairs 3 gang switch, via the 2 core which are the strappers. At top switch single from common to light.

Do you have just the one lighting circuit? You may or may not have a shared neutral.

The 3 core cable method was indeed introduced (during the late 50's -early 60's) as a way of converting an exising one-way circuit to two-way without having to interfere with the connections. This method was quite useful as such, but hardly logical since it required five wires at one switch - when a 2-way switch having just three terminals should only require three wires.

However, this 3C&E method is the only method of 2-way switching known to younger sparks, so they just don't consider the alternative methods - which don't include the use of the shared ("borrowed") neutral.

Heaven knows what they do when they have multi-gang multi-two-way switching, when T&E cables would better serve as strappers.

Lucia.

well thanks for the compliment, although I am a younger spark so I think you kinda insulted me toward the end of your post

Oh really?

It's most unlike me, to be insulting..........

Lucia.

Its OK, water off a ducks back is the saying, so I believe.

John

I was always taught to use 3 core on two way and two way and intermediate switching to reduce RFI interference.

However, this 3C&E method is the only method of 2-way switching known to younger sparks, so they just don't consider the alternative methods - which don't include the use of the shared ("borrowed") neutral.

The 3C&E conversion method makes a borrowed neutral less likely as one cable drops from the rose with the live and switch output in it. Therefore you don't need to find a live on another floor.

That just isn't so AndyPRK.

For a start, the 3-core conversion method was developed to convert any 1-way circuit to 2-way which might well have been on the same floor and in the same room of that floor - so there was no question of finding another live or sharing another neutral. The method was devised as a way of linking two switches without having to disturb the connections in the light fitting.

It isn't logical for a 2-way switch to have five cores connected to it when it has only three terminals - and in the case of multi-gang 2-way switches, it's absolutely barmy to cram the switch box with multilple 3-core cables, when T&E would better serve as strappers. This doesn't mean that a shared neutral would have to be used. Some of you youngsters can't consider more economic methods of cabling on 2-way circuits without using 3-core.

Lucia.

Simply taking two single and earth cables from the rose to either switch with strappers between is no different from taking a twin and earth to one switch and a three core linked between the two switches in regards of the amount of work to be done.

As junction boxes and saving cable were all the rage then, it was common to only have a single 3 core cable at each two way switch. It also meant you didn't have to worry about getting two cables down existing switch drop conduits.

1John: Your idea might be well and good on a single 1-way circuit, but on multi-way, 2-way circuits, it just doesn't make sense to cram the switch with so many wires.

A 2-way switch has just three terminals. Therfore, it only needs three wires.

Take the case of a 3-gang, 3x2-way switch: An inexperienced spark would install 3x3core and 3x2 core there, making a total of fifteen cores when in fact a total of only seven wires would do the job: one wire per terminal plus two common links.

Lucia.

If you grab the other end of the stick you may see that I agree with you

However, this 3C&E method is the only method of 2-way switching known to younger sparks, so they just don't consider the alternative methods - which don't include the use of the shared ("borrowed") neutral.
Lucia.

Maybe you could answer the question rather than avoiding it. Or say your wrong.

Using the example in this thread of the landing light, with a switch down stairs and one switch upstairs. And a light upstairs.

The upstairs and downstairs lights are on different circuits. (different RCBOs)

How is the old method of twin and earth between the switches less likly to have a borrowed neutral (or borrowed live)?

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