Normally Open vs. Normally Closed: What Does it Mean?

Normally Open vs. Normally Closed: What Does it Mean?

When it comes to electrical switches, there are two main types: normally open and normally closed. But what does that mean? In this blog post, we will discuss the difference between these two types of switches and provide some examples. We will also explain when each type is typically used. Stay tuned!

Normally Open

A normally open switch is one that is open when not actuated. That means that, in its unactivated state, there is no path between the electrical contacts. When you push the button or flip the lever, it closes the circuit and completes the path, allowing current to flow [1].

In simple terms: Normally open means the switch is off until you turn it on.

Normally Open

Uses for Normally Open Switches

There are a lot of applications for NO switches. A few examples include:

  • Automotive fuel injectors – They are open when the engine is off (to prevent fuel leakage) and closed when the engine is on.
  • Burglar alarm systems – The switch is usually placed on a door or window. If the door or window is opened, the circuit is broken and the alarm sounds.
  • Fire sprinkler systems – The switch is located in the piping. If the temperature gets too high, the switch opens and water flows into the piping. In addition, you may be interested in interfacing a flame sensor with Arduino guide.
  • Conveyor belts – The switch is usually located at the end of the belt. If something breaks the beam of light, the switch will open and the conveyor belt will stop.
  • Some computer keyboards – The switch is located under the key. When you press the key, the switch closes and a signal is sent to the computer.
  • Automatic doors – The switch is located in the sensor. When someone or something breaks the beam of light, the switch closes and the door opens.
  • Fire alarm release button – The switch is located in the button. When the button is pressed, the circuit is completed and the fire alarm sounds.
  • Emergency stop buttons – The switch is located on the button. The switch closes and the machine stops when the button is pressed [2].

In these two previous applications, it is vital that the switch not be accidentally triggered. If the switch were to close when it should be open, or vice versa, it could have disastrous consequences.

NO switches are also used in more mundane applications such as vending machines and office equipment. They are often used in appliances such as coffee makers and microwaves. Many electronic devices use NO switches to control the flow of electricity.

There are many other applications for NO switches. If you can think of any, please share them in the comments!

Normally closed

In a normally closed circuit, the switch is closed, and the current can flow freely through the circuit. The term “normally closed” refers to the default state of the switch. In other words, when the power is off or when there’s no input signal, the switch is in the closed position [3].

To make it clear, let’s take a look at an example.

Say you have a light switch in your living room that controls a lamp. When you want to turn the lamp on, you push the switch down to close the circuit and allow the current to flow. The switch is “normally closed” because when there’s no input (when your hand isn’t pushing the switch down), the circuit is still closed and the current can flow.

Normally closed

Uses for Normally Closed Switches

There are many uses for normally closed switches. They can be used as safety devices, to control lights, limit switches, and in-process control applications.

  • One of the most common uses for a normally closed switch is as a safety device. A switch that is configured in this way will prevent equipment from starting up if there is a problem with the circuit. This can help to prevent accidents and injuries.
  • One more use for a normally closed switch is to control lights. These switches can be used to turn on and off a light fixture. They can also be used to dim or brighten a light.
  • Limit switches are another common use for normally closed switches. These switches are used to control the movement of a machine or process. They can be used to turn off equipment if it reaches a certain point, or to prevent it from moving beyond a certain point.
  • In-process control applications are another area where normally closed switches are used. These switches can be used to monitor and control the flow of materials or liquids. They can also be used to regulate the temperature of a process.

These are just a few of the most common applications. If you have a need for a switch that will keep a circuit closed, a normally closed switch is the right choice.

How do you wire these types of switches?

To wire a normally open switch, you need to connect the two wires that go to the load (or device that you want to control) to the two terminals on the switch.

To wire a normally closed switch, you need to connect one wire to one terminal on the switch, and the other wire to the other terminal.

If you need to wire a switch that is both normally open and normally closed, you will need to use two switches.

You can wire them in parallel so that they both control the load, or in series so that one switch controls the other switch, which then controls the load.

It’s important to know which type of switch you need for your application.

There are a few things to keep in mind when wiring a switch.

  • First, make sure that you have the correct type of switch for your application.
  • Second, make sure that you connect the wires to the correct terminals on the switch.
  • And third, make sure that you do not create a short circuit.

Short circuits can occur when the wires that are connected to the switch are touching each other, or if the wire that is connected to the load is touching one of the terminals on the switch.

If you have a short circuit, it can cause damage to your switch, your load, or both.

So it’s important to be careful when you’re wiring a switch.

Read more guides to upgrade your knowledge in electronics:


Are electrical contacts drawn normally closed open or both?

This is a great question! The answer depends on the situation. If you’re talking about a switch, for example, it can be either normally open or closed.

If you’re talking about an electrical circuit, it’s usually drawn as either normally open or closed. However, there are some instances where both may be used.

Is normally open positive or negative?

There is no positive or negative when it comes to normally open or closed. It simply refers to the position of the switch.

Useful Video: Basic Electrical – Normally open and Normally closed

Final Thoughts

There you have it! Now you know the difference. As always, if you have any questions or need help selecting the right type of switch for your application, please contact us. We’re here to help!

What other types of switches would you like to see a blog post about? Let us know in the comments below!

I hope this helped clear things up for you and as always, thanks for reading!

Until next time!