<P> A normally open (NO) contact pair is open (in a non-conductive state) when it, or the device operating it, is in a deenergized state or relaxed state . </P> <P> The National Association of Relay Manufacturers and its successor, the Relay and Switch Industry Association define 23 distinct forms of electrical contact found in relays and switches . Of these contact forms, the following are particularly common: </P> <P> Form A contacts ("make contacts") are normally open contacts . The contacts are open when the energizing force (magnet or relay solenoid) is not present . When the energizing force is present, the contact will close . An alternate notation for Form A is SPST - NO . </P> <P> Form B contacts ("break contacts") are normally closed contacts . Its operation is logically inverted from Form A. An alternate notation for Form B is SPST - NC . </P>

What does nc and no mean in electrical terms