6 - Switches in Series

 

S.P.S.T. switches can be connected in series (as shown in the diagram). In the circuit, the multimeter is testing the voltage, or potential, across the lamp. It shows us how the switches need to be positioned, in order to allow current to flow through the circuit and light up the lamp.

Switches in Series

The slider switches in this circuit "make" when they are put to the "1" position.

Click the series switches to find the required positions to make the lamp light.

 

An Example of Series Switching: Workshop machines, that have high-powered motors, often use moveable safety guards to protect the user. To check these are all in place, switches wired in series are positioned close to the guards and only made to "close" when the guards are in the shut position. In this arrangement, the operator cannot turn the motor on unless two guards are in place.This is due to the two "protection" switches being connected in series with the third main operator on/off switch.

We can write a logical statement to describe this. First we will call the two protection switches; "switch 1" and "switch 2" and the main on/off switch: "switch 3". We will also say, if any switch is closed it is in state "1" and if it is open it is in state "0".

Logic Statement

If switch 1 AND switch 2 AND switch 3 are "1" then the motor will turn on.