What are the “NO” and “NC” Contacts of the Relay

We often see “NO” and “NC” in some information related to the relay. However, do you know what do “NO” and “NC” stand for and what are they really mean?

“NO” stands for “normally open”. A contact that is normally open when it is not powered on is called a normally open contact. “NC” stands for “normally closed”. A contact that is in a closed conduction state when it is powered off is called normally closed contact. 

Take the following picture as an example. It is a schematic diagram of a relay. 1 and 2 are working coils and 3 is a common point; 3 and 4 is a set of normally closed contact, and 3 and 5 is a set of normally open contact. When coils 1 and 2 are connected to the appropriate power supply, 3 and 4 will be open, and 3 and 5 will be closed.