Otis Singleton
In electrical engineering, NO and NC are terms used to describe the states of a contactor when the voltage in an electrical system is off. NO stands for normally open, which means that the wire connected to this contact will normally be open or off, and the current will not flow when the relay is deactivated. NC, on the other hand, stands for normally closed, which means that the contactor will close a circuit in the event of a voltage drop or power failure. These terms are essential for designing circuits and writing PLC programs that control various functions, providing the foundation for building logic by allowing users to specify how a system behaves under different conditions.
| Characteristics | Values |
|---|---|
| Full Form | NO: Normally Open |
| NC: Normally Closed | |
| Description | When the relay coil is not energised, the switch contact in the NO system is open or disconnected. |
| When the relay coil is not energised, the switch contact in the NC system is closed or connected. | |
| Use Cases | NO is used in electrical systems where, for safety reasons, you want to be sure that the contactor opens when the power is cut in the system in case of a power failure. |
| NC is used when you want to be sure that the contactor closes a circuit in the event of a voltage drop, such as a power failure, to drain the system of energy to earth. | |
| NO and NC are used for any mechanical switch, not just electrically-actuated ones. They are also used with switches, in addition to relays, with the same meanings. |
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What You'll Learn
- Normally Open (NO) and Normally Closed (NC) are electrical engineering terms
- NO and NC are used for any mechanical switch, including toggle switches
- NO and NC are essential for designing circuits and writing PLC programs
- NO and NC contacts work in opposite ways: when one is working, the other is off
- NO is used for safety, while NC is used to drain the system of energy
Normally Open (NO) and Normally Closed (NC) are electrical engineering terms
Normally Open (NO) and Normally Closed (NC) are terms used in electrical engineering to describe the state of a contactor when the voltage in an electrical system is off. In an electrical relay system, there are two types of contacts: Normally Open (NO) and Normally Closed (NC). This is because the current path can either be open or closed.
Normally Open (NO) contacts are used in electrical systems where, for safety reasons, it is important to ensure that the contactor opens when the power is cut or in the event of a power failure. When the relay is activated, the circuit is connected, and the current flows. When the relay is inactive, the circuit is disconnected, and the current does not flow.
Normally Closed (NC) contacts are used when it is necessary to ensure that the contactor closes a circuit in the event of a voltage drop or power failure, allowing the system to be drained of energy. When the relay is activated, the circuit is disconnected. When the relay is inactive, the circuit is connected.
Both NO and NC contacts are essential for designing circuits and writing PLC programs that control various functions. They provide the foundation for building logic by allowing for the specification of system behaviour under different conditions.
It is important to note that NO and NC can be used with switches in addition to relays, and they have the same meanings in the context of mechanical switches.
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NO and NC are used for any mechanical switch, including toggle switches
NO and NC are terms used in electrical engineering, especially when designing circuits and writing PLC programs that control various functions. They are used to describe the state of a contactor when the voltage in the system is off.
NO stands for "Normally Open", which means that the switch contact is open or disconnected when the relay coil is not energised. This is commonly used in electrical systems where, for safety reasons, it is important to ensure that the contactor opens when the power is cut or in the case of a power failure.
NC stands for "Normally Closed", which means that the switch contact is closed or connected when the relay coil is not energised. This is used when it is necessary to ensure that the contactor closes a circuit in the event of a voltage drop or power failure, allowing the system to be drained of energy.
Both NO and NC are used for any mechanical switch, including toggle switches, and they can be used in combination with each other. For example, a Single Pole Single Throw relay will only have a normally open contact, but a Single Pole Double Throw relay will have both. When a current flows through the relay coil, the magnetic field it creates pulls the switch over, opening the NC contact and closing the NO one.
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NO and NC are essential for designing circuits and writing PLC programs
In electrical engineering, NO and NC stand for "normally open" and "normally closed", respectively. These terms refer to the state of a contactor when the voltage in an electrical system is off. Normally open (NO) contacts are used in electrical systems where safety is a priority, ensuring that the contactor opens when the power is cut or in the event of a power failure. On the other hand, normally closed (NC) contacts are used when it is essential to close the circuit during a voltage drop or power failure to drain the system of energy.
NO and NC are integral to the design of circuits and the writing of PLC (Programmable Logic Controller) programs. PLCs are industrial digital computers used for controlling manufacturing processes, such as assembly lines and robotic devices, where reliability, programming ease, and process fault diagnosis are crucial. Understanding the behaviour of NO and NC contacts under different conditions is essential for building logic into these systems.
For example, in a relay system, NO and NC contacts are the only types available because the current path can either be open or closed. A relay may have both a normally open contact and a normally closed contact. When the relay is activated by a power supply, the internal circuitry is triggered, causing the normally open contact to close and allowing current to flow. Simultaneously, the normally closed contact opens, disrupting the previously closed circuit.
The behaviour of NO and NC contacts can be manipulated to achieve specific outcomes. For instance, in package door latches, momentarily powering the coil can open the NC contact and close the NO contact. However, sustaining a constant voltage across the coil is not advisable as it can reduce the coil's lifetime.
In summary, NO and NC contacts are fundamental to circuit design and PLC programming, providing the basis for creating logic and specifying system behaviour under various conditions. Their ability to control the flow of current makes them essential components in electrical engineering and automation.
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NO and NC contacts work in opposite ways: when one is working, the other is off
In electrical engineering, NO and NC contacts are essential terms used in designing circuits and writing PLC programs that control various functions. They are part of a relay, which is a type of electrically-actuated mechanical switch. The terms refer to the state of a contactor when the voltage in the system is off.
NO stands for "Normally Open", which means that the switch contact is open or disconnected when the relay coil is not energised. This type of contact is used in electrical systems where safety is a concern, as it ensures that the contactor opens when the power is cut. When the relay is activated, the contact closes, and the current can flow.
NC stands for "Normally Closed", which means that the switch contact is closed or connected when the relay coil is not energised. This type of contact is used when it is important to ensure that the contactor closes a circuit in the event of a voltage drop or power failure, allowing the system to be drained of energy. When the relay is activated, the contact opens, and the current is interrupted.
As NO and NC contacts are always part of the same relay, they work in opposite ways. When one is working and the current is flowing, the other is off and the circuit is interrupted. For example, when the relay is energised and the NO contact is closed, allowing current to flow, the NC contact is open and the circuit is disconnected. Conversely, when the relay is not energised and the NC contact is closed, the NO contact is open.
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NO is used for safety, while NC is used to drain the system of energy
In electrical engineering, NO and NC stand for 'normally open' and 'normally closed', respectively. These terms describe the state of a contactor when the voltage in the system is off. In an electrical relay system, these are the two types of contacts available, as the current path can either be open or closed.
A normally open contact will be off when the relay is deactivated, and the current will not flow. When the relay is activated, the internal circuitry of the relay is triggered, which closes the contact and allows the current to flow through. Normally open contacts are typically used in electrical systems for safety reasons, to ensure that the contactor opens when the power is cut in the event of a power failure.
On the other hand, normally closed contacts connect the circuit when the relay is inactive. When the relay is activated, the circuit is disconnected. Normally closed contacts are used when it is important to ensure that the contactor closes a circuit in the event of a voltage drop, such as a power failure, to drain the system of energy to earth.
Both NO and NC contacts are essential for designing circuits and writing PLC programs that control various functions. They provide the foundation for building logic by allowing for the specification of system behaviour under different conditions.
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Frequently asked questions
NO and NC stand for Normally Open and Normally Closed.
Normally open (NO) contacts connect the circuit when the relay is activated. The circuit is disconnected when the relay is inactive. Normally closed (NC) contacts disconnect the circuit when the relay is activated. The circuit is connected when the relay is inactive.
Understanding NO and NC is essential for designing circuits and writing PLC programs that control various functions. They are the foundation for building logic by allowing you to specify how the system behaves under different conditions.
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