What is a contactor, is a question a new automation engineer might ask.

Industrial automation involves lots of integrated components.

Contactors are electrically controlled switches.

Contactors use a lower voltage and current, such as 230VAC (Volts Alternating Current), to switch a larger voltage and current.

An example of the use of a contactor in industrial applications, is in DOL starters.

DOL is an abreviation of Direct-On-Line, and is a type of industrial starter, typically used to operate Induction Motors.

An induction Motor is commonly used in factories.

DOL starters operate in two states, namely ON or OFF.

If an induction motor has a steady operating current draw of 15 Amps, then this can present wiring issues.

In order to directly switch the Induction Motor on, you would need a switch and cabling, capable of handling that much current.

The current rating would actually need to be at least 20% higher, to handle what is known as ‘in- rush current’.

In-rush current can be likened to a petrol car accelerating from standstill.

In our car example, more fuel would be used to start the car accelerating, than would be used once it was at cruising speed.

Therefore Induction Motors draw more current when starting to turn, from standstill.

Back to our DOL starter, cabling and switch would have to be large.

Contactors switch large currents, and can be located near the Induction Motor.

The control switch can be located at a distance from the DOL starter unit, containing the contactor.

Low voltage , low current rated cabling from the control switch saves money, and makes the system easier and cheaper to install.

Control switching can use single phase to operate the contactor, which switches on three phase.

Published by Craig Miles

Craig Miles

Leave a comment

Your email address will not be published. Required fields are marked *