Normally Open Contact Numbers

87a normally closed contact.

Normally open contact numbers.

In other words when voltage is applied to the relay contactor terminals this contact closes. 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. If it is a switch then it is off. The contacts are open when the energizing force magnet or relay solenoid is not present.

When the energizing force is present the contact will close. 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. 87b normally open contact. Normally closed nc contacts allow current through when the relay or contactor is not energized.

Normally open no contacts allow current when the relay or contactor is energized. 85 relay coil 86 relay coil 87 common contact. Normally open is a contact that does not flow current in its normal state. This is simply the state that the contact is in when something else is not affecting it.

An alternate notation for form a is spst no. Form a contacts make contacts are normally open contacts. Din 72552 defines contact numbers in relays for automotive use. When voltage is applied this contact opens and interrupts current.

If it is a relay then it is not energized.