Page 102 - Electrician - TT (Volume 2)

ELECTRICIAN - CITS

Contactors: The contactor forms the main part in all the starters. A contactor is defined as a switching device
capable of making, carrying and breaking a load circuit at a frequency of 60 cycles per hour or more. It may be
operated by hand (mechanical), electromagnetic, pneumatic or electro-pneumatic relays.
The contactors shown in Fig 1 consist of main contacts, auxiliary contacts and no-volt coil. As per Fig 1, there
are three sets of normally open, main contacts between terminals 1 and 2, 3 and 4, 5 and 6, two sets of normally
open auxiliary contacts between terminals 23 and 24, 13 and 14, and one set of normally closed auxiliary contact
between terminals 21 and 22. Auxiliary contacts carry less current than main contacts. Normally contactors will
not have the push-button stations and O.L. relay as an integrated part, but will have to be used as separate
accessories along with the contactor to form the starter function.
The main parts of a magnetic contactor are shown in Fig 1 shows the schematic diagram of the contactor when
used along with fused switches (ICTP), push-button stations and OL relay for connecting a squirrel cage motor for
starting directly from the main supply. In the same way the direct on-line starter consists of a contactor, OL relay
and push-button station in an enclosure.

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CITS : Power - Electrician & Wireman - Lesson 70-75 CITS : Power - Electrician & Wireman - Lesson 70-75