Otis Singleton
In electrical wiring, N/C stands for normally closed, which means that the switch contact is closed, and current can flow. On the other hand, N/O stands for normally open, which means that the switch contact is open, and the circuit is disconnected. These terms are used for any mechanical switch, not just electrically-actuated ones, and are also used with relays.
| Characteristics | Values |
|---|---|
| Full Form | Normally Closed |
| Circuit | Closed (current can flow) |
| Relay Coil | Closed when not energized |
| Relay | Part of a relay or relay-like components |
| Switch | Used for any mechanical switch |
| Schematic Diagram | N/C is used to indicate a closed switch |
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What You'll Learn
Normally Open (NO) means no current flows
The terms "normally open" and "normally closed" refer to the default states of contacts in a switch or relay. They describe whether the contacts are open or closed when there is no external influence. Understanding these terms is essential in electrical wiring and control automation.
Normally Open (NO) means that the switch will be in the open position, and no electricity flows unless an input signal is provided. In other words, a circuit with NO contacts will be open or disconnected when the relay is inactive. When the switch is actuated or activated, the contacts close, allowing current to flow through the circuit. For example, a doorbell requires you to push a button to close the circuit and ring the bell.
The use of NO contacts in a circuit can be a safety feature, ensuring that electricity will only flow as long as the operator or product is physically engaged. As soon as the input energy is removed, the circuit returns to the open position, and electricity ceases to flow. This characteristic of NO contacts is valuable in various applications, such as emergency stop buttons, where it is crucial to interrupt the flow of current immediately.
Understanding the behaviour of NO and NC contacts is crucial when designing electrical systems. In some cases, the wrong selection and design can lead to issues, such as damaging the bearings of an electric motor. Therefore, it is essential to carefully consider which instrument switches or discrete equipment to use in a process, choosing between NO and NC sensors and switches appropriately.
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Normally Closed (NC) means current can flow
In electrical wiring, NC stands for "normally closed". This is a term used to describe electrical contacts. Normally closed (NC) means that the contacts are closed, and current can flow. When a relay is inactive, the circuit is connected, and current can flow through it.
NC contacts are the opposite of NO contacts, which stand for "normally open". NO contacts are open or disconnected when the relay is off or inactive. In this case, the circuit is open, and current does not flow.
NC and NO contacts are used in relays and switches. A relay is a type of electrically-actuated mechanical switch. It uses an electromagnet to operate an armature, which in turn operates the switch mechanism. The switch mechanism can be a set of NC contacts, a set of NO contacts, or a combination of both.
In a Single Pole Single Throw (SPST) relay, there is only a normally open contact. A Single Pole Double Throw (SPDT) relay will have both a normally open and a normally closed contact. Other variations of relays also exist with multiple combinations of NC and NO contacts.
NC contacts are often used in emergency push buttons and stop push buttons. For example, in a factory setting, a low-level switch may be a Normally Closed switch. When the oil level in a tank drops below this switch, it sends a signal to a PLC (Programmable Logic Controller) to turn off the electric motor. This prevents damage to the bearings of an expensive electric motor.
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NO and NC are used for mechanical switches
In electrical wiring, N/O and N/C are acronyms for "Normally Open" and "Normally Closed", respectively. They are used to describe the two states of a mechanical switch. A Normally Open (NO) switch has open contacts when it is inactive, and a Normally Closed (NC) switch has closed contacts when it is inactive. These switches are often used in relays or relay-like components, such as solid-state relays or modules.
NO and NC switches are essential in various devices for safety and operational efficiency. For example, in an emergency stop button, an NC switch ensures that the machine stops when triggered, while a NO switch allows operations to start or continue when pressed, such as with a machine start button. The correct application of these switches is crucial for ensuring device safety and functionality across industries.
NO and NC switches are also used in combination in some applications, such as in an excavator's hydraulic arm control switch. In its normal state (NC), the switch keeps the hydraulic arm raised, maintaining a safe workspace. When the operator activates the switch to NO, the hydraulic arm lowers to engage with the ground or materials, enabling digging or lifting operations. The NC/NO function allows the operator to override standard operations for specialized tasks, optimizing the excavator's utility with a single control switch.
In addition to their use in relays and machinery, NO and NC switches are also commonly found in push-button form. These push buttons can be momentary, where the button reverts to its original state after release, or latching, where the button does not revert to its initial state upon release. Momentary push buttons are perfect for applications that require fast response times and precise control, such as industrial machinery and safety systems. Latching push buttons, on the other hand, are ideal for situations where continuous control is needed without the need to hold down the button, such as lighting controls and security systems.
The functionality of NO and NC switches is crucial in various electrical systems, providing both operational efficiency and safety measures. Understanding the difference between these two types of switches is essential for designing and maintaining reliable and safe electrical systems.
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NO and NC are relay connections
In electrical wiring, N/C stands for "normally closed", while N/O stands for "normally open". These terms refer to the default state of a relay's contacts when it is not energised.
The NO and NC connections are used in various relay setups, such as those for motor forward and reverse operation, light switching, and 3-way switching. Proper wiring techniques are crucial for effectively using these connections in relay setups. For NC contacts, the wiring should ensure that the circuit remains closed until the relay is activated. This typically involves connecting the load to the NC terminal and the common terminal. This configuration ensures that the circuit is complete and allows current to flow through the load when the relay is not energised.
For NO contacts, the wiring should keep the circuit open until the relay is activated. This involves connecting the load to the NO terminal and the common terminal. In this setup, the circuit remains open and prevents current flow when the relay is not energised. Regular maintenance and careful installation practices can significantly reduce problems and ensure reliable relay operation.
In summary, the NO and NC connections in a relay setup are essential for controlling the flow of current in a circuit. Proper wiring and maintenance techniques are crucial for ensuring the reliable operation and longevity of the relay and the overall system.
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NO and NC sensors and switches are used in industry
In electrical wiring, N.C. stands for "normally closed", which means that the switch contact is closed, i.e. connected, when the relay coil is not energised. N.O., on the other hand, stands for "normally open", which means that the switch contact is open, or disconnected, when the relay is inactive.
NC sensors, however, are crucial in emergency and safety applications. Emergency push buttons and stop push buttons typically use Normally Closed contacts. When activated, these contacts open the power circuit, immediately halting the process. In the event of cable damage, the circuit remains open, ensuring that the process is stopped. This is a safer option than risking a non-functional emergency circuit.
In real-world conditions, the selection of NO or NC sensors depends on the specific application and the type of equipment being used. For example, in a lubrication system for a 1MW electric motor, a Normally Closed switch is used as the low-level switch. When the oil level drops below the switch due to a leakage, the switch sends a 24-volt DC signal to the PLC, which then turns off the electric motor and sends an alarm to operators.
Additionally, NAMUR switches, which are based on milliampere signalling, are used in hazardous areas to limit voltage and current, preventing sparking during switching.
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Frequently asked questions
N/C stands for "Normally Closed" and is used to describe electrical contacts. It means that the switch contact is closed, i.e. the circuit is connected when the relay is inactive.
N/O stands for "Normally Open". In this case, the circuit is open (no current flows) and the switch contact is disconnected when the relay is inactive.
N/O and N/C are used to describe mechanical switches, including electrically-actuated ones. On a schematic diagram, N/O and N/C will not usually be labelled but will be represented by symbols.
A low-level oil switch in a 1MW electric motor can be a Normally Closed switch. When the oil level is below the switch, it sends a signal to a PLC, which turns off the electric motor and sends an alarm to operators.
