Switches play a key role in controlling the flow of electrical current, especially in circuits and wires. As such, they are present in diverse appliances, from home equipment to large scale machines. Regardless the operational mechanism, Normally Open vs Normally Closed switches is crucial to consider appropriate switch selection. Let us delve into this in detail!

Figure no 1 NO vs NC

1) What’s a switch?

“Essentially a switch can be defined as an electrical device that makes or breaks an electric circuit.”

The primary function is to inversely turn the flow of current on or off while allowing manipulation of the device connected. The devices may be like, lights, fans and other apparatuses.

There are toggle, push, and rocker switches, etc. Every type is intended for different purposes in terms of their construction and use appliances. Regardless of different types, their purpose ranges from the basic requirement of turning on or off the circuit.

In an equal context, switches provide comfort as well as security measures. For example, they allow ensuring electrical circuits to be turned off when they are either being repaired or in case there is an emergency. In contrast, most of the current models are designed with recommended factors of dependability, durability and ease. It ensures that they are useful in modern homes and industries.

2) Basic Principles of Switch Operation

Switches join or separate parts of an electrical circuit to control appliances, either turning them on or off. They achieve this by moving two terminals toward each other or apart.

• In an open circuit, the switch prevents electric current from flowing, keeping the connected device off.
• Conversely, in a closed circuit, the switch allows current to flow, enabling the connected device to operate.

Figure no 2 NO and NC

These may include switches like light switches, while automated switches, such as pressure and temperature switches, respond to specific conditions. The design depends upon the specific function and application.

3) What is a Normally Open (NO) Switch?

NO switch can be defined as typically a spring loaded switch, and is OFF until turned ON. Meaning in its natural position there is no electrical current that flows through the circuit. When you push the switch, you complete the circuit and hence allowing electric current to flow.

Figure no 3 NO circuit

• Main characteristics

• The default state is open which is off.
• To complete the circuit, it requires user activation
• Commonly used in applications where by default the system will be OFF, but the circuit can be activated using a switch.

• Applications

• Doorbell circuits: This means that the electric circuit is open until someone presses on the button to close the circuit in order for the bell to ring or sound.

• Customer Feedback: It is used in the apps, or surveys to decline offers, services. It may also used to provide a negative response to a question.

• Design variations of Normally Open switches

• Normally Open push button Switch: It is a type of switch that toggles between the ON and OFF positions with the default state being the OFF position.

• Momentary Close Push Switch: A switch that starts the flow of electricity through a circuit while it is pressed, and stops it when not pressed.

• Default Open Rotary Switch: Rotary switches are used to open and close electric connections. It has a rotating dial for ON and OFF. They are set to the OFF position when not in use.

4) What is a Normally Closed (NC) Switch?

A Normally Closed contact switch is normally in the ON position. This means that current flows through the circuit at all times unless some external force causes the switch to open the circuit, thus stopping current flow.

Figure no 4 NC circuit

• Key Characteristics

• Default state: Closed
• Need to break the circuit to activate the switch further.
• This configuration focuses on fail-safe or safety applications, as the circuit remains on by default. And turns off only when someone specifically acts to do so.

• Applications

• Emergency stop buttons function in a normally closed mode. A simple NC circuit shuts down or interrupts work immediately.

• When the refrigerator door shuts, a light switch ensures the light turns off. Opening the refrigerator door activates the switch, turning the light on.

• Design variations of Normally Closed switches

• Rotary Normally Closed Switch: A circular rotating switch in which closing controls operate in a sequence that includes a self-fastening rotary action.

• Key-Lock Normally Closed Switch: Close circuit switches that need a key to turn them.

5) Key Differences Between Normally Open and Normally Closed Switches

Understanding the differences between NO and NC switches is really important for selecting the right one for your application. Here’s a breakdown of their key differences:

6)  Applications of NO and NC Switches

• Applications of Normally Open Switches:

i) Push-to-Start Systems: Mostly applicable in motors and machines where some activation is required in order to start functioning.

ii) Alarm Systems: Applicable when an alarm goes off on a specific trigger condition (a button has to be pressed, for example).

iii) Control Panels: Applicable in industries for specific functions to be switched on manually.

• Applications of Normally Closed Switches:

i) Safety Circuits: Applicable in halting operations instantly in occasions of emergency.

ii) Automation Systems: In situations wherein there is the constant functioning of the processes until a particular event occurs that interrupts the circuit.

iii) Security Systems: Where breach sensitive places such as doors or windows are installed. The alert goes off the moment the circuit is interrupted.

7) Installation Considerations

• Installation Considerations for NO Switches:

a) Disconnect the power supply before installing a switch.

b) Connect the switch to the circuit that actuates the device.

c) Place it at spots where users need to press it to trigger alarms or start the system.

d) Wire it properly to prevent accidental activation.

Figure no 5 Installation considerations

• Installation Considerations for NC Switches:

a) The application should involve the circuits that would be required for continuous operations i.e. safety control circuits, and monitoring circuits.

b) The switch should be placed in the right position to help immediately in case of an emergency alarm.

c) Confirm that all wires are securely connected to avoid cut off any part of the circuit by mistake.

d) One more point to consider is the installation should be away from combustible or explosion-sensitive materials.    

8) Choosing the Right Switch for Your Needs

So yes, choosing a switch can definitely be a daunting task as there are so many available options. But when broken down to a few key aspects, it becomes the job easier whether it is a Normally Open Normally Closed switch. Here are recommendations;

! Default state requirements: This one is a bit self explanatory to most, do you need the circuit open (NO) or closed (NC) at power up. For instance, an NO switch is ideal for systems that operate on demand only and not in the standby mode, for instance, a door bell switch.

Conversely, there are applications for NC switches, which when powered on enables the system to run on constantly. And hence, these are applicable in case of safety monitoring systems.

! Safety: For applications where safety is an issue, the NC switches are normally used. These are such that all the systems are left working until it is turned off. And hence, used for situations like an emergency stop or for a fail safe mechanism.

! Ease of Use: Determine the manner in which the switch will be actuated. When a mechanical action is likely to be carried out repeatedly, it is important that the switch is conveniently located and is easy to operate. For control systems, the switch should be designed to blend in well with control mechanisms.

! Environmental Factors: Think about the environment where the switch is expected to be applied. Industrial areas may need switches that are water resistant, dust resistant, resistant to extreme hot or cold temperatures etc.

! Cost vs Performance: Even though there is always a need to balance with the budget, ensure that quality does not suffer. A good switch will ensure that there are minimal system upsets and will cut down maintenance costs over time.

To find out more information and explore great selection of switches, check out CDOE PushButton. They have ON and NC switches and NO and MC, that can be used for different needs. Moreover, CDOE Push Buttons are tasked with effective response of any type, whether it is alert, access control, or industrial uses.

Figure no 6 CDOE push buttons

These buttons have been manufactured while bearing in mind their usage across different commercial, residential and even industrial sites in tough environments. Their simplicity in use and sturdiness offers great opportunities for improvement of the safety and efficiency of the operations. From emergency stops and pushing doors to a number other uses, the Push Button of the CDOE has emerged as an effective and reliable solution ever.

9) Future trends

The market for switching technology is growing significantly and slowly switching from NO and NC switches to more advanced technology. The total switch revenue worldwide is expected to rise by US $2.10 billion from 2020 from a level of US $ 20 billion by the year 2030 representing a 4.8% annual growth rate.

Smaller non-mechanical switches that consume less power are also gaining a broader market in medical devices and also in wearable devices. In addition, switches which are rugged enough for extreme environments especially automotive and aerospace also have a booming market. There is also a demand for greener energy harvesting switches that work from the energy produced by their own motion.

10) FAQ

1. Do All Switches have NO/NC Contacts?

No, not all switches include NO contact or NC contact points. Lock out switches – multi position switches when exposed to multiple positions don’t work that way. However, toggle and push button switches do have NC and NO purposes, but it is not all usages.

2. Can normally open and normally closed contacts be interchanged?

With regards to such contacts it is almost always the case that they are not interchangeable without drastic alteration of the circuit. So, the switch you use should be in accord with the needs of the application.

3. How can you tell if a switch is normally open or normally closed?

To tell the difference between an NC and NO switch:

• Examine the specifications or labels provided by the manufacturer.
• A continuity test through a multimeter can also be used.
• An NC switch will show continuity in its relaxed state while NO will not.