Normally Open Contact Numbers

Normally open no contacts allow current when the relay or contactor is energized.

Normally open contact numbers.

Din 72552 defines contact numbers in relays for automotive use. If it is a switch then it is off. If it is a relay then it is not energized. 87b normally open contact.

Energizing it and switching it on will close the contact causing it to allow current flow. In other words when voltage is applied to the relay contactor terminals this contact closes. An alternate notation for form a is spst no. 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.

This is simply the state that the contact is in when something else is not affecting it. When the energizing force is present the contact will close. If it is a high limit such as a temperature alarm then the current temperature is below the limit. 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. Form a contacts make contacts are normally open contacts. When voltage is applied this contact opens and interrupts current. Of these contact forms the following are particularly common.

The contacts are open when the energizing force magnet or relay solenoid is not present.