page 579

34. IMPLEMENTATION

34.1 ELECTRICAL

34.1.1 Electrical Wiring Diagrams

•PLC’s are generally used to control the supply of power to a system. As a result, a brief examination of electrical supply wiring diagrams is worthwhile.

•Generally electrical diagrams contain very basic circuit elements, such as relays, transformers, motors, fuses, lights, etc.

•Within these systems there is often a mix of AC and DC power, but 3 phase AC power is what is delivered universally by electric utilities, so the wiring diagrams focus on AC circuits.

•A relay diagram for a simple motor with a seal in circuit might look like the one shown below,

page 580

M

L1

step down transformer

start

stop

M

M

• The circuit designed for the motor controller must be laid out so that it may be installed in an insulated cabinet. In the figure below, each box could be a purchased module(s).

page 581

A Physical Layout for the control cabinet

• After the Layout for the cabinet is determined, the wire paths must be determined. The figure below lays out the wire paths, and modules to be used.

page 583

•The last section contained an example of an electrical control system for a motor. It used a number of symbols to represent elements.

•The Joint International Committee (JIC) developed a standard set of symbols for representing electrical circuit elements. These are given below.

page 584

F

page 585

H1 H3 H2 H4