Dual control switches are the double pole type switches which are generally used at the top and bottom of a starcase, or at the opposite ends of a long corridor, etc. With such switches, the appliance (say, a bulb) can be switched on or *** from, two different places.
The working and circuits of a dual control switch are illustrated in Fig. a,b,c. Let a switch S1 be fitted at the top of the staircase.
Fig. (a) shows the *** position of the bulb.
The bulb can now be switched on independently by either the switch S1 or the switch S2 If the switch S1 is operated, the connection ‘ab’ is changed to ‘bc’, which completes the circuit and the bulb lights up [Fig. (b)]. Similarly, on operating the switch S2 , the connection ‘bc’ changes to ‘ba’, which again completes the circuit
[Fig. (c)].
Similarly, if the bulb is in on position as shown in Fig. (b), one can switch *** the bulb by changing the connections ‘ab’ to ‘bc’ either by the switch S1 or the switch S2.
In a starcase, while going up a person puts on the light by operating the switch S1 so that the connection ‘ab’ changes to ‘bc’ and makes the current to flow in the circuit. On reaching at the top of operates the switch S2 to put the light so that the connection ‘cb’ changes to ‘ba’ and the flow of current stops. The same system is operative when a person puts on light by operating the switch S2 to change the connection ‘cb’ to ‘ba’ and switch the light by operating the switch S1 to change the connection ‘ab’ to ‘bc’.
