On Wednesday, November 30, 2016 at 11:48:51 AM UTC, DICEGEORGE wrote:
I seem to recall reading somewhere that in 2 way switching for house lighting its a good idea to have a neutral wire parallel to the lives to cut down on interference, is this so? In which case I need 4 core and earth not 3 core and earth.


http://wiki.diyfaq.org.uk/index.php/2_Way_Switching

[g]

http://www.theiet.org/forums/forum/m...threadid=28561
says:

Paul1966

Posts: 1538
Joined: 21 December 2004


The key point is that whatever current flows in one direction along a conductor in a cable should also flow in the opposite direction along another conductor in that cable.

In a single 2C(+E) cable running to a light, the instantaneous current at any moment in L is counteracted by an equal current in N flowing in the opposite direction. In a 2C switch loop, both conductors are live, but the instantaneous current flowing to the switch at any instant in time is balanced by an equal current flowing in the adjacent conductor back from the switch.

This principle just extends to 3C cable and multi-way switching. You might have three conductors in the cable, but for any given combination of switch positions only two will be carrying current, and those currents will be flowing in opposite directions.