Normally Open Contact Numbers

This is simply the state that the contact is in when something else is not affecting it.

Normally open contact numbers.

When voltage is applied this contact opens and interrupts current. Normally closed nc contacts allow current through when the relay or contactor is not energized. 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. 87a normally closed contact.

In other words when voltage is applied to the relay contactor terminals this contact closes. When the energizing force is present the contact will close. Energizing it and switching it on will close the contact causing it to allow current flow. 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. Din 72552 defines contact numbers in relays for automotive use. 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. An alternate notation for form a is spst no. If it is a switch then it is off. The contacts are open when the energizing force magnet or relay solenoid is not present.

Of these contact forms the following are particularly common.