Magnetic relay or just called relay is a type of switch that is controlled by an electric current. The main part of relay consists of a coil and contacts. Relay coil wrapped around the core. There is an iron armature will be attracted to the core when a current flows through the coil. Armature is mounted on a spring-loaded lever. When the armature attracted to the core, relay contact will change its position from normally closed contacts to the normally open contacts.

A relay can be activated in about 10 ms. Most relay placed in packaging that fully closed, as shown below.


Most among the relay has contacts type of SPDT switch, but there are also several types of DPDT switch, TPDT switch (Triple Pole Double Throw) and QPDT switch (Quadruple Pole Double Throw, as shown above right).

The important thing to note on a relay that will be used is the coil voltage and the maximum, current and voltage contacts.

Larger relays can be connected to the currents up to 10 A at a voltage of 250 VAC. The DC maximum voltage for switching is always lower than AC maximum voltage, sometimes even just half of the AC maximum voltage.

Symbol relay with QPDT contact switch

Symbol relay

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