Normally Open Contact Numbers

Normally open is a contact that does not flow current in its normal state.

Normally open contact numbers.

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

If it is a high limit such as a temperature alarm then the current temperature is below the limit. Energizing it and switching it on will close the contact causing it to allow current flow. 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. Of these contact forms the following are particularly common.

If it is a switch then it is off. If it is a relay then it is not energized. The contacts are open when the energizing force magnet or relay solenoid is not present. 85 relay coil 86 relay coil 87 common contact.

An alternate notation for form a is spst no. This is simply the state that the contact is in when something else is not affecting it. 87a normally closed contact. 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.

When the energizing force is present the contact will close.