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.

See Also

Wiring colour codes

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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