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Posted By Topic: Different 2-way wiring

Mar 21 2018 14:29

Hi All,

I\'m trying to see how the wiring for 2 way light switches outlined here and how that actually works? From what I see, each light switch needs an active in TPS cable? Is that how that can get away with not having 3 wires between the 2 switches as outlined in the attached diagram from the Standards doc? Which I find is odd anyway since the only Red/White/Blue cable I\'ve seen states is typically used in Airconditioning cable?

Mar 21 2018 16:06

Your question is not that clear but there are two common methods for doing a two way circuit.
One is what I call the conduit method which only requires two switching conductors between the switch mechs. The active feed comes in at one end and the lighting load is connected at the other end .
A lot of schematic diagrams still use this layout , what is not normally clear though is that you still need a neutral at the switch the light is supplied from if you are using TPS cable so you still need at least three cores at that switch. Now you can\'t use red , white, Blue , for that you need a black.

The second and probably more common method is to take the Active feed and the lighting load to the same switch and run a three core red, white , blue , to the other end .
This method is normally way easier to wire in practice when using TPS cable.

Mar 21 2018 17:53

\"Now you can\'t use red , white, Blue , for that you need a black.\"
True, but you can sleeve one of the RWB cores as black.
You also need to get PEC to the lighting point, which is easy in conduit; or TheDon\'s second method (with feed & load at same end), but otherwise needs a 3&E for the strap.


Mar 25 2018 21:20

I came across an interesting (!) 2-way arrangement in an old house.
The two 2-way switches had the common switching between L and N. The light was connected between the commons of the two switches.
So in the OFF position the light had N on both contacts ... or P.
Now that\'s what I call different 2-way wiring!

Mar 25 2018 22:39

Oh dear! According to that website

\"You cannot get a shock by touching the NEUTRAL wire.
You cannot get a shock by touching the EARTH wire.
You cannot get a shock when touching the ACTIVE wire. You must touch the ACTIVE and NEUTRAL or ACTIVE and EARTH.\"

Mar 26 2018 01:47

SaintAlan, The switching you describe wouldn\'t be legal.

Mar 26 2018 09:49

Aleck so even if it is the remote end of a 3 core strap with no other wiring at that plate, you still have to run an earth conductor to it? i.e. 3 core and earth strap.

Mar 26 2018 11:17

Only need it for \"lighting points\"; so with the feed & load at same end the other end of the strap doesn\'t need an earth (unless some thing else there counts as \"conductive building materials\"

Mar 26 2018 11:37

Thanks Aleck must have been a typo in your above comment you said 3 core and earth strap.

One other way I came across was the feeding of two lights on a two way over some stairs. The previous electrician had wired one light with a neutral to a sub board upstairs with no RCD protection and the other light had a neutral to the main switch board which was RCD protected. It made for some interesting switching and tripping when a new lamp was installed to replace a lamp that had blown. Was a PIA to figure out and put right. Junction boxes with new and old wiring everywhere in the roof space.

Mar 26 2018 11:47

You need to read the whole paragraph. He said to get the PEC to the lighting point you can use 3core and earth.

Mar 26 2018 12:22

Thanks Doug, I now see that he is talking about if the light switched wire is at the opposite end of the strap to the feed.

Mar 26 2018 13:31

SaintAlan notes: I came across an interesting (!) 2-way arrangement in an old house.

What you came across is called a California three way.

I\'ve no idea where the \"California\" comes from, other than the obvious, but it\'s a \"three way\" because \"three way\" is an Americanism for what the rest of the world calls a \"two way\".

Not so useful in a house, but handy when the lighting was the outside lighting to an outbuilding, by running just three overhead conductors one could have two-way light switching for the light outside the shed or garage, and have sockets and locally controlled lights in the shed or garage.

I\'ve never heard of this arrangement used in a 240V country, so where was this seen?


Mar 26 2018 13:59

I always thought a \"California three-way\" would need mutually consenting adults

Mar 26 2018 14:12


Mar 26 2018 14:13

And I guess that does fit in with the Americans engorging their number of ways.

Mar 26 2018 15:43

\'What you came across is called a California three way.\'
Ah, so that is what it\'s called. At the time there were some rather un-PC comments about Irish and Tangata Whenua jobs. But many things about that place (an old villa renovation) were not kosher, like the complete absence of a main earth.
Don\'t worry dbbuckley, it is all rewired to the regs now.