Quick electric wiring query

aliasojo

During the work that's going on in my house, I've come across a wire to a light switch that has at one point been screwed or nailed (although there is nothing in it now). The yellow wire is all but broken through, it's literally hanging by a thread.

As the floors are up, I've traced it back to another light switch and can run new cable to replace it. As all cable has new colours now, which colour is the equivalent of the blue, yellow and red?

AdrianW2

http://diydata.com/electrics/cable_colour/cable_colour.php

It's all a bit of a mess really; brown, black and grey are all phase colours leading to much confusion for those of us that subconsciously expect black to be neutral, and of course people are still using black as neutral when using 3 core and earth.

I don't think there's any hard and fast rule as to which colour should be which. UltimateHandyman suggests using grey as common.

zax47

Contrary to what Adrian thinks, there IS a hard an fast rule about which colours replace which under the new European harmonised cable colour coding and these are defined explicitly in BS7671:2008, the 17th Edition wiring regulations; Section 514.3 (and table 7A in appendix 7 thereof).

It is vital you follow these to protect anyone who may work on the circuit after you!

old-> new
red-> brown
yellow-> black
blue-> grey

The grey and black wires should have brown tape (or sleeving) at each end to denote their live status. Yellow was always "common" in two way circuits, ergo this would now be black (it is in all my installs!!)

AdrianW2

I don't have a copy of the standard in front of me* but doesn't that appendix just show how the colours of the phase conductors have changed?

Pre-harmonisation it was common to use yellow (L2) as common in a 2-way light switch, but there's no rule that says L2 has to be used in that role and in my limited experience most people don't anymore, preferring to connect L1 (brown) to the terminal marked L1 and L2 (black) to the terminal marked L2. Everything liberally sprinkled with brown sleeving.

...but Zax is the professional, and I'm just trying to help.

* this is what happens when you delegate legislation writing to profit making bodies

zax47

The table defines the designations of L1, L2 and L3 as being Brown, Black and Grey respectively, for use in all mutliple live/phase applications. By this definition (and that fact that we were taught to use L2 (Yellow) for common in two way circuits) it means what was Yellow is now Black. Once you get the Black=neutral out of your head then it makes things easier.

Having said all that, and putting the "rules" to one side, in a two way switching application as long as you get boths end connected the same it doesn't matter from a practical/operational point of view.

aliasojo

Thank you very much both. I'll follow the colours you listed above, zax.