PLC Logic Example on Multiple Switches and Motors

Learn the PLC logic example on multiple switches and motors with the ladder diagram.

This PLC logic example is prepared for the engineering students to learn and practice the ladder logic. The design of the same PLC program for industrial usage will be different.

PLC Logic Example

Problem Statement:

Design a PLC ladder logic for the following application.

There is a use of four toggle switches to control four motors.

If Switch 1 is ON, then Motor I will be ON.

If Switch 2 is ON, then Motor I and Motor II will be ON.

If Switch 3 is ON, then Motor I, Motor II, and Motor III will be ON.

If Switch 4 is ON, then Motor I, Motor II, Motor III, and Motor IV will be ON.

Inputs of PLC

The list of the digital inputs for this PLC logic is mentioned below.

Switch 1: I0.0

Switch 2: I0.1

Switch 3: I0.2

Switch 4: I0.3

Outputs of PLC

The required digital outputs are listed below.

Motor 1: Q0.0

Motor 2: Q0.1

Motor 3: Q0.2

Motor 4: Q0.3

Multiple Switches and Motors Ladder Logic

Here is the PLC logic for the given problem statement.

Program Explained

For this example, we used Schneider PLC software for programming.

In the above PLC program, we have used Normal Open Contact for Switch 1 (I0.0), Switch 2 (I0.1), Switch 3 (I0.2) and Switch 4 (I0.3)

Switch 1, Switch 2, Switch 3, and Switch 4 are connected in parallel for Motor 1, thus implementing OR logic gate.

For Motor 2, inputs switch 2, switch 3, and switch 4 are connected in parallel, thus implementing OR logic gate.

Switch 3 and switch 4 are implementing OR logic gate i.e., connected in parallel for Motor 3.

Only Switch 4 is connected to Motor 4.

For Motor 1 to be ON, either Switch 1 or Switch 2 or Switch 3 or Switch 4 should be ON.

To turn ON Motor 2, either Switch 2 or Switch 3 or Switch 4 should be ON.

When Switch 3 or Switch 4 is ON, then Motor 3 will turn ON.

Motor 4 will turn ON when Switch 4 is turned ON.

PLC Simulation Results

Next, we will see the PLC simulation results with different input switch ON and OFF combinations.

When Switch 1 is ON

When the toggle switch 1 is turned ON, the current flows through it (here we are using the term “Current” in case of an electrical circuit, so here you can assume it as “Current” or simply call it as “Signal”).

As a result, Motor 1 gets ON. Other motors will remain OFF because Switch 1 is not connected to them.

When Switch 2 is ON

The current will flow through switch 2 when it is turned ON that will turn ON Motor 1 and Motor 2. It is so because switch 2 is connected to Motor 1 and Motor 2 only.

When Switch 3 is ON

When Switch 3 is turned ON, the current flows through it that will turn ON three motors i.e., Motor 1, Motor 2 and Motor 3. The input switch 3 is connected to these outputs only. Motor 4 will remain OFF as Switch 3 is not connected to it.

When Switch 4 is ON

Switch 4 will turn ON all the motors when turned ON. Switch 4 is connected to all the motors, when turned ON, Motor 2, Motor 2, Motor 3 and Motor 4 will turn ON.