Normally Open Contact Numbers

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

Normally open contact numbers.

87a normally closed contact. An alternate notation for form a is spst no. 87b normally open contact. 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. 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 relay then it is not energized.

The contacts are open when the energizing force magnet or relay solenoid is not present. 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. Of these contact forms the following are particularly common.

When voltage is applied this contact opens and interrupts current. Din 72552 defines contact numbers in relays for automotive use. Normally closed nc contacts allow current through when the relay or contactor is not energized. If it is a switch then it is off.

When the energizing force is present the contact will close.