In: Electrical Engineering
Provide an example application that uses normally open relay Contacts and normally closed relay contacts?
#Normally Open relay contact: Normally open relay contacts are majorly used to latching or activate another device or circuit.
Above ladder diagram shows the use of Normally open contact's of a relay. Here a start pushbutton is used to actuate the relay CR1. One NO contact of CR1 is used parallel to start button for latching mechanism. Another NO contact of CR1 is used to activate an output (in this case a motor).
#Normally Close relay contacts: Normally close relay contacts are majorly used for safety interlocking or for inverting output (such as actuating relay deactivate the output).
In above ladder it shows a mechanism to operate a motor in either forward or in reverse direction. As we can see NO contacts are used for interlocking purpose. NC contacts of each relay in connected in the actuation path of the other relay in series. Due to this, the motor is not able to run in both forward and reverse condition in same time. Either this if by mistake both the relay is activated in same time short circuit will occur in motor. Thus the use of NC is safety purposes.