Contactors and relays


    Contactor is a remotely controlled electric switch designed for different current intensities and number of poles. The switching itself is made by an electromagnetic coil designed for different voltages. A contactors consists of main contacts – through which the load is connected to its power supply - and auxiliary contacts – which serve for control and signalization.

Auxiliary contacts are

  • NC – under normal conditions they are close
  • NO – under normal conditions they are open

Important parameters in contactor selection:

  1. rated operational current
  2. rated control circuit voltage
  3. switching current of auxiliary contacts



    Relay is an electrical component consisting of a switch and an electrical coil (electromagnet) which, as a result of an electric current, switches on or off the electric current in the second circuit.
    Electromagnetic relays are devices most frequently used in control and automation technologies. They are composed of a coil (electromagnet) and normally open, normally closed, or changeover contacts. A relay is in fact the simplest amplifier. It means that through a small control current in the control circuit we control (switch on and off, switch over) big currents flowing through the contacts. With one relay (one control circuit) we can control more circuits simultaneously also at large distances (circuits controlled can be electrically isolated and supplied with different voltage). If the relay is operating (there is a current in its coil), NO contacts are closed, NC are open, change-over NO/NC contacts are switched over.