Electrical switches are the brains of the electrical circuits— they control, operate, and synchronize the current flow! Switches come with two fundamental configurations.
First— Closed switch. Second— open switch. Each switch features a different design, operability, and applications. Therefore, engineers must sort out their installation based on the working mechanisms.
This guide is for you— we will dive deep into the switches and understand their differences.
What Is A Normally Closed Switch?
Normally, closed switches are those types of switches that have a closed circuit system, and positive and negative terminals meet in default state. Current flows when not activated and turns off when you activate them.
How does it work?
The working mechanism of a circuit depends on its closed or open configuration.
The working mechanism is straightforward.
- There is a contact between the positive and negative terminals of the circuit.
- Current flows normally in the default state.
- Activation of switches turns off the current flow.
Such switches are fail-safe because they open up in case of system failure and protect the users from accidents.
What Is A Normally Open Switch?
The name is enough to elaborate on the circuit presence of such a switch. A normally open switch has an open by default.
Since the circuit is open, there is no current flowing through the circuit normally. Therefore, we call them open switches. They are opposite to the normally closed switches.
How does It Work?
The working mechanism of the normal switch depends on whether you have activated it or not. Let’s understand when the switch is inactive.
In a normally open switch:
- There is no contact between the terminals.
- The circuit is open and doesn’t conduct electron flow.
- Current flows through the circuit only if you press the activation button.
Such switches hold a strong presence in the power buttons and initiation circuits.
Key Differences Between NC and NO Switches
NO and NC switches have a different circuit structure and the presence of electron flow. Let’s have a comprehensive debate on this aspect.
| Feature | Normally Closed (NC) Switch | Normally Open (NO) Switch |
| Default State | The circuit is closed (current flows) | The circuit is open (no current flows) |
| Activation Behavior | Opens circuit when activated | Closes circuit when activated |
| Power Consumption (Idle) | Consumes power | No power consumption |
| Safety Use | Ideal for safety and fail-safe systems | Not ideal for fail-safe; used for optional or triggered actions |
| Response Time | Immediate response in case of failure | May introduce delay due to activation requirement |
| Durability | Wears faster due to constant use | Longer lifespan due to less frequent activation |
| Common Applications | Emergency stop, limit switches, alarms, security systems | Doorbells, control panels, start buttons, relays |
| Multimeter Test (Idle) | Low resistance (closed path) | Infinite resistance (open path) |
| Control Over Operation | Less control; always conducting unless triggered | More control; conducts only when needed |
| Energy Efficiency | Less energy-efficient | More energy-efficient |
Default State Comparison
The default state is the actual presence of the circuit. We have already discussed the normal state of both switches. Let’s expand our painting here.
NC switches have some unique features in the default state. For example:
- Both terminals of the circuit are joined.
- Electrons flow between positive and negative electrodes, leading to current presence in such circuits.
- Activation of such a circuit bottlenecks the current effectively.
On the other hand, NO switches share some salient features in the default state.
- There is no contact between the electrodes. Therefore, the electron flow is not possible. The current doesn’t flow normally.
- The circuit is open.
- Closing the circuit requires an external force to join the opposite electrodes.
Behavior When Activated
Activation means the opposite action compared to the default state. NO and NC switches have an opposite 180-degree behavior.
NC switches normally have a closed circuit. Once you apply external force, the contact between the terminals breaks. As a result, electron flow stops and current stops. This is an active state of the NC switches. If you remove the force, the circuit again completes, and current flows through the circuit.
NO switches do exactly the opposite of the NC switches. Upon activation, the first phenomenon is the contact between positive and negative terminals. Current flows when such a switch is active.
Use Cases and Applications
Both switches have different mechanisms of action. As a result, they have unique applications.
NC is useful in:
- Emergency Stop Buttons.
- Limit Switches.
- Fail-safe Circuits.
- Security Systems, such as door sensors.
NO is a priority for:
- Momentary Push Buttons, such as doorbells and keyboards.
- Relay Control Inputs
- Start Buttons in industrial machinery
- Safety Devices.
Advantages and Disadvantages
Let’s break down both switches and discuss their pros and cons.
NC switches
The positive points are:
- Constant current flow in the default state allows continuous system monitoring until you apply force.
- Good for safety and fail-safe design, as the circuit opens when a failure occurs.
- It causes immediate action when the switch is triggered.
The drawbacks include:
- NC switches consume power in an idle state and can create more energy loss.
- Constant operations of circuit electrodes cut the life short. Such switches offer less durability due to continuous usage.
NO switches
The advantages include:
- No power consumption in the idle state so that you can save more energy.
- It is ideal for triggering circuits on demand as you have better control over whether and when to turn on the switch.
- NO switches offer reduced wear because they conduct and use circuits only when it is crucial.
The pitfalls are:
- It is unsuitable for applications needing constant monitoring, as an external force is necessary to operate it.
- NO often induces delay because you must apply the external force to the current flow. The system fails when you need a fast response.
Conclusion
Switches are the basic layers of the electronic circuits and serve as the gatekeepers. They provide critical safety during the system operations.
NCs are fail-safe, while the NO offers efficient control of the system. In emergency and safety operations, you should choose the NC, while NO is for general applications.
FAQs
1. Can a normally closed switch be used as a safety feature?
Yes, 100%. Normally, closed switches open the circuit when there is a loss of control or system failure. Therefore, they are a trump card in the critical system where failures can occur.
2. Can normally closed switches be used in high-voltage applications?
Yes. You can use the normally closed switches in high-voltage applications, but with several concerns:
- Voltage and current should match the application requirements.
- Safety measures should be taken beforehand.
- Use relays for a very high voltage.
3. Which is the more reliable switch: Closed or Open?
Reliability depends on the applications and conditions. For example, normally closed switches are ideal and reliable for safety applications, while general applications place more trust in the open switches. Both switches respond differently to dust and moisture. So, consider them accordingly for the given applications.
4. How do you test if a switch is NO or NC?
Testing a NO or NC switch is straightforward.
- Cut the power source.
- Get a multimeter to test the resistance.
- An NC switch shows lower resistance by default, while an NO switch shows infinite resistance by default.
- Actuate both switches, and you’ll see the inverse resistance (NO shows low resistance while NC shows endless resistance).
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