What are Normally Open (NO) & Normally Close (NC) Contacts in Ladder Logic

For working in the PLC programming, either you are using Siemens PLC software, Fatek PLC software or Mitsubishi PLC software, or any other PLC programming software, we must know about ladder logic language. There are some functions we have in ladder logic which are most important for creating the PLC program in any PLC programming software. In this article, we are going to discuss and learn about NC (Normally close) contact and NO (normally open) contact in ladder logic programming.  Let's start learning normally open and normally close (NO and NC) from normally normally close contact one by one.

What is Normally Close Contact

Normally close or NC contact means circuit is closed in normal condition. For example, as we have a fuse in electrical circuit, it close the circuit in normal situation until it break and make circuit open. This means current is keep flowing to the circuit until fuse break the circuit.

When we energize this NC (normally close) contact in ladder logic programming, this contact change itself from close to open, and it will open the circuit.

What is Normally Open Contact

Normally open or NO contact means circuit is open in normal condition. For instance, as we have a circuit breaker in the circuit which is switching the circuit ON and OFF. Same situation is in our ladder logic programming, we use normally open contact (NO Contact) to switch the circuit ON. This normally open (NO contact) will allow the current to flow, when it will be energized.

For example, we have to switch ON our output number 1, with a push button, which is connected to our input number 1 right? We use normally open contact here for push button input signal. This normally open contact will allow current to flow to the output number 1, and output will be switched ON. This is like circuit breaker.


I hope you have learned about normally open and normally closed. I will try to teach more about them in our ladder logic programming tutorials.