Introduction to Industrial Automation

Table 2.1  Standardized Values for Nominal 

Voltage Selection of a Relay Coil

Values of Relay Coil Nominal Voltage

AC 50 Hz

24, 42, 48, 60, 110, 230, 380 V

DC

12, 24, 36, 48, 110, 230 V

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  Introduction to Industrial Automation

to the mechanical one because the contact life is application-dependent, such as when a set of 

contacts switches a load of less than rated value.

The power relays, except for their three main power-contacts (one for each phase of the three-

phase network), may be equipped with one or more pairs of auxiliary contacts, which are used in 

the implementation of the automation circuit. Figure 2.8 shows a typical form of a power relay 

Fixed core

Moving

core

Coil cross section

Return

spring

Cable

terminals

Fixed

contact

Moving

contact

Arc

chamber

Metal or alloy

contact area

Insulation material

On-state

indicator

Moving

core

Return

spring

Cable

termina

Fixed

contact

contact area

indicator