Introduction to Industrial Automation

Figure 1.10  Examples of power circuits: (a) Single-line, three-phase circuit design, (b) complete 

multi-line design of circuit, and (c) circuit design of a direct starting motor.

50 Hz 230 V

R

Overload relay

contact

Stop button

Start button

Relay

contact

Relay

N

Figure 1.11  Example of a simple automation circuit.

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  Introduction to Industrial Automation

It should be noted that in the wiring diagram of Figure 1.12, the wires can intersect among 

each other and thus it is very difficult to follow the route of each wire and the overall functional-

ity of the design, even in this very simple case, where we have only four devices (one relay, two 

buttons, and one overload protection). Having this in mind, it can be easily generalized how this 

complexity will grow in cases with more intersections, e.g., in wirings with 50 devices. In contrast 

to this, in the automation circuit of Figure 1.11, there are no wiring intersections and thus it is 

very easy to follow and understand the overall operation logic. For this reason, automation circuits 

provide an overview of the automation functionalities are most commonly utilized during the 

development, installation, and operation of an automation system.

Automation circuits are being developed in branches (sectors), which are presented in 

Figure 1.13. Each branch denotes the operational function of a corresponding relay, solenoid, 

50 Hz 380 V

R

S

T

N

M

3 ~

Stop

St

ar

t