What is the difference between NO and NC of the push button switches?

Terminal color distinguishes NO and NC contacts

Some push button switches can be distinguished from the color of the terminal. This is to avoid operation errors. Generally, the button caps are made of different colors. Green (or blue) is NO contact, and red (or pink) is NC contact.

Terminal distinguishes NO and NC contacts

The NO and NC contacts can be distinguished directly from the terminal. Generally speaking, the upper end is the NC contact, and the lower end is the NO contact. This is the simplest way to judge, but there will be certain errors, so you can’t just use this method to judge NO and NC contacts.

Accurately measure NO and NC contacts with a multimeter

1. First set the multimeter to the on-off gear, that is, the diode buzzer gear, and then touch the two contacts of the push button switches with two meter pens. If there is a sound, it means that the contact is NC, otherwise it is NO. We can press the button to measure again, and we will find that the result is exactly the opposite of the above.

2. First adjust the multimeter to the electrical barrier, that is, 1K, and use two meter pens to respectively touch the two contacts of the push button switches. When there is a resistance value, it is NC (the resistance value is very small, normally between 0.2-1, this Is the internal resistance of the multimeter). If there is no resistance value, it is NO. We can press the button to measure again, and we will find that the result is exactly the opposite of the above.

What is the use of push button switch NO and NC two contacts?

The NC contact is used to connect the circuit when you press it down.

Under normal circumstances, there will be a maintenance relay in this circuit to keep the circuit connected. In this way, when you release the push button switch, the loop remains energized through the maintenance relay, allowing the system to operate normally. Until the termination signal such as close button or emergency stop arrives.

Because some occasions need to use NO contacts, some occasions need to use NC contacts, such as the start button to use NO, stop button to use NC, in order to be universal, the push button switches is usually equipped with two contacts of No and NC (constitute one No contact, one NC contact). The difference between it and the lighting panel switch is that as soon as the button is released, the contact will return to the state when it was not pressed (there are also buttons that can be held). There is no protection function. The lighting panel switch is a circuit breaker with load protection and short circuit protection. If there is no malfunction, it will remain closed until someone pulls it open. (Extended learning: Why is it safer to use normally closed contacts for emergency stop buttons? )