2 Way Switching
2 way switching means having 2 or more switches in different locations to control one circuit. They are wired so that operation of either switch will control the light(s).
To achieve 2 way control the usual single switch is replaced with either of the following circuits:
a ------o------------------------------------o L1
\
O--------------------------------O COM
\
b ------o------------------------------------o L2
switch cable run switch
Alternative method of Two Way Switching:
o------------------------------------o L1
/
a ----O O----- b COM
/
o------------------------------------o L2
switch cable run switch
3 Way Switching:
a ------o---------------o o----------------o L1
\ \ /
O---------> X <---------O COM (not connected at X)
/ \ \
b ------o---------------o o----------------o L2
switch cable crossover sw cable switch
Alternative method of 3 Way Switching:
o---------------o o----------------o L1
/ \ /
a ----O X O----- b COM
/ \ /
o---------------o o----------------o L2
switch cable crossover sw cable switch
- a & b are the 2 connections that are used in place of the usual single switch (i.e. one connected to live, and the other is the switched live return to the ceiling rose or lamp fitting)
- the switches at each end are 1 pole 2 way switches
- Any number of crossover switches may be added to give 3 or more way switching.
- the cable runs are from one switch location to another
- 3 core & earth cable is usually used for 2 way switch circuits.
Notes:
The first example given in each case is the preferred connection method, as it is less likely to cause interference problems with electronic systems. (The example given in the electrical regulations is inductive hearing loop systems but similar considerations apply to computer networks and other wired systems.)
The alternative circuits appear to require one less wire but in reality is is usually necessary to return the COM connection at the second switch position to the first switch or the rose or light fitting which typically needs a wire. They are included here as they are often encountered in older wiring.
Carter system
Another 2 way switching method exists and is occasionally encountered. Its called the Carter system (other names are also used).
The lights run off wires A and B. A switch at one end switches wire A between live and neutral. The switch at the other end switches wire B between live and neutral. Thus the lights can see 2 neutrals, 2 lives or one of each.
This approach leaves the supply to the holder live when switched off, creating a very slight risk. It also feeds live and neutral to the poles of a switch, and switches do mechanically fail, creating the risk of a short. For these reasons this method has long been non-compliant, and should not be used.
See Also
Keywords
Two way, two way switching, two way switch, intermediate switch, multiple light switches, switching a light from two locations, twin switches, two way wiring, hearing aid compatibility, remote switching