Normally Open and Normally Closed electrical contacts make up electrical switches, relays, circuit breakers, and most any other electrical component that switches something on/off or can be switched on/off.

What is open and closed? Before we get into what normally open and normally closed are, let's clarify what "open" and "closed" mean. As with so many topics that we try to simplify by associating with something we are familiar with, associating electrical current flow with water flow causes a tremendous amount of misunderstandings. Whereas, we open a water faucet to start water flow, we close an electrical contact to start current flow, and instead of closing a water faucet to stop water flow, we open an electrical contact to stop current flow. IMPORTANT CONCEPT:

Closed = Current flow
Open = No current flow

What is normally? This is simply the state that the contact is in when something else is not affecting it. If it is a relay then it is not energized. If it is a switch, then it is off. If it is a high limit such as a temperature alarm then the current temperature is below the limit.

Normally open - Is a contact that does not flow current in its normal state. Energizing it and switching it on will close the contact, causing it to allow current flow.

Normally closed - Is a contact that flows current in its normal state. Energizing it and switching it on will open the contact, causing it to not allow current flow.

Electrical Contacts - Normally Open And Normally Closed Contacts

Normally Open and Normally Closed electrical contacts make up electrical switches, relays, circuit breakers, and most any other electrical component that switches something on/off or can be switched on/off.