Normally Open Contact Numbers

If it is a switch then it is off.

Normally open contact numbers.

This is simply the state that the contact is in when something else is not affecting it. When voltage is applied this contact opens and interrupts current. If it is a high limit such as a temperature alarm then the current temperature is below the limit. 85 relay coil 86 relay coil 87 common contact.

87b normally open contact. Normally open no contacts allow current when the relay or contactor is energized. When the energizing force is present the contact will close. In other words when voltage is applied to the relay contactor terminals this contact closes.

The contacts are open when the energizing force magnet or relay solenoid is not present. Normally closed nc contacts allow current through when the relay or contactor is not energized. Energizing it and switching it on will close the contact causing it to allow current flow. 87a normally closed contact.

An alternate notation for form a is spst no. If it is a relay then it is not energized. A relay contact in the ladder diagram can be normally open or normally closed and there is no limit to the number of contacts a relay can have. Normally open is a contact that does not flow current in its normal state.

Out coils a plc output is really just an internal relay with a physical connection that can supply electrical power to control an external load.