Normally Open Contact Numbers

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

Normally open contact numbers.

In other words when voltage is applied to the relay contactor terminals this contact closes. Energizing it and switching it on will close the contact causing it to allow current flow. If it is a relay then it is not energized. Form a contacts make contacts are normally open contacts.

87b normally open contact. If it is a switch then it is off. 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. 85 relay coil 86 relay coil 87 common contact.

Din 72552 defines contact numbers in relays for automotive use. When voltage is applied this contact opens and interrupts current. An alternate notation for form a is spst no. Normally open is a contact that does not flow current in its normal state.

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. The contacts are open when the energizing force magnet or relay solenoid is not present. This is simply the state that the contact is in when something else is not affecting it. Of these contact forms the following are particularly common.

87a normally closed contact.