RLD Symbols

Normally Open

Normally Open Contact (NO):-  

The Switch is disconnected in normal condition and when relay coil is activated or external pressure is applied it connects the circuit, also called Make contact, closes the circuit when the relay coil is activated. Generally represented as an open switch, shows when pressed makes contact and works as an ON switch.

Normally connected

Normally Closed Contact (NC):-  

The Switch is connected in normal condition and when relay coil is activated or external pressure is applied it disconnects the circuit, also called break contact, breaks the circuit when the relay coil is activated. Generally represented as an closed (connected) switch, shows when pressed breaks contact and works as an OFF switch.

Relay Coil:-  

The relay coil is represented by an electrical block that also works as an output for the switch based logic. The control of the power supply to the relay coil can be activate the NO/NC of the external contacts which can be used to turn ON or OFF any connected circuit.

Example:-  

If we are given a switch and we need to turn on the relay coil in such a way that whenever the switch is pressed the O/P turns On then the RL design for such an logic will be as follows: