Trystan Casey
Electrical contactors are a crucial component in electrical engineering, used to control the flow of electricity to various electrical circuits. They are used to switch power to a circuit repeatedly and are designed to perform this task over thousands of cycles. Contactors are almost always set up in a 'normally open' (NO) configuration, which means that the circuit will only be established while the electromagnet in the contactor is receiving current. In this setup, there is no direct connection between the PLC and the motor, allowing the user to turn on and off a high-voltage electric motor indirectly and safely.
Characteristics and Values of NO (Normally Open) on an Electrical Contactor
| Characteristics | Values |
|---|---|
| State when voltage is off | Open |
| Usage | Safety reasons, to ensure the contactor opens when the power is cut |
| Application | Electrical systems |
| Coil | Low voltage |
| Connection to PLC | Indirect |
| Circuit | Established when the electromagnet in the contactor is receiving current |
| Contacts | Three |
| Contact Type | Auxiliary, feedback, spring-loaded, power |
| Contact Material | Alloys of tungsten, molybdenum, copper, silver with cadmium oxide |
| Contact Operation | Open or close |
| Contact Protection | Bifurcated contacts, contact wipe |
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What You'll Learn
NO means 'normally open'
An electrical contactor is a crucial component in electrical engineering, used to control the flow of electricity to various electrical circuits. It is designed to manage the power supply to a load, such as a motor or lighting system. Contactors are used in a wide range of situations where there is a need to switch power to a circuit repeatedly. They are typically used for higher power applications than relays, allowing low voltages and currents to switch or power cycle a higher voltage/current circuit on and off.
NO, in this context, stands for 'Normally Open'. This describes the state of a contactor when the voltage in the system is off. In a normally open configuration, the circuit will only be established while the electromagnet in the contactor is receiving current. When the contactor is energised by pressing a 'start' button, the normally open contact between terminals 13 and 14 closes, creating a pathway for the current to flow.
Contactors with a normally open configuration are often used in electrical systems where, for safety reasons, you want to ensure that the contactor opens when the power is cut in the system in case of a power failure. This configuration is also useful when there is a need to switch power to a circuit frequently or rapidly.
The three core components of an electrical contactor device are the coil, the contacts, and the device enclosure. The coil, or electromagnet, is the key component. When the coil is energised, a magnetic field is created, which attracts the moving core of the contactor. The contacts are the components that carry power across the circuit being switched. The contactor enclosure insulates and protects the contactor's key components.
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NO contacts establish a circuit when activated
An electrical contactor is a crucial component in electrical engineering. It is a type of switch that can turn on and off a large amount of current with a small control signal. Contactors are used to control electric motors, lighting, heating, capacitor banks, thermal evaporators, and other electrical loads. They are also used to switch power to a circuit repeatedly.
NO, or Normally Open, describes the state of a contactor when the voltage in the system is off. When the contactor is designed as normally open, exciting the coil with voltage will push the contacts together, establish the circuit, and allow power to flow around the circuit. This is how most contactors are designed. When the coil is energised, an electromagnetic field is created, which causes the contacts to be closed. This is how a circuit is established.
The contacts are the components of the device that carry power across the circuit being switched. They are the current-carrying part of the contactor and are typically made of metal. Each type of contact performs a specific function in transferring current and voltage. Contacts can be spring-loaded, which interrupts an electrical circuit if the contactor is powered off.
The coil, or electromagnet, is the key component of a contactor. When the coil is energised, it creates a magnetic field, which attracts the moving core of the contactor. The force developed by the electromagnet holds the moving and fixed contacts together. When the contactor coil is de-energised, gravity or a spring returns the electromagnet core to its initial position and opens the contacts.
NO contacts are 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.
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NO contacts are used for safety
NO, or Normally Open, refers to the state of a contactor when the system is off. In this state, the circuit is interrupted and power cannot flow. When the coil is energised, the contacts are pushed together, establishing the circuit and allowing power to flow.
In contrast, NC, or Normally Closed, refers to a contactor that completes the circuit when de-energised. This type of contactor is often used when it is necessary to drain the system of energy in the event of a power failure.
Contactors are used to control high-power circuits and electrical devices such as motors, fans, pumps, lighting, heating, capacitor banks, and thermal evaporators. They are designed to handle a large amount of current with a small control signal, allowing low voltages and currents to switch a far higher voltage/current circuit on and off.
Contactors are a crucial component in electrical engineering, providing a level of safety by isolating high-power circuits. They also increase the safety and reliability of the system by preventing electric shocks, short circuits, and overloads.
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NC contacts are the opposite of NO
Electrical contactors are used in a wide range of situations where there is a need to switch power to a circuit repeatedly. They are designed to perform this task over many thousands of cycles. Contactors are typically used for higher power applications than relays, allowing low voltages and currents to switch or power cycle a higher voltage/current circuit on and off.
The three core components of any electrical contactor device are the coil, the contacts, and the device enclosure. The coil, or electromagnet, is the key component. When the coil is energised, an electromagnetic field is created, which causes the armature within the contactor to move in a certain way regarding the electrical contacts. The contacts are the components that carry power across the circuit being switched. The contactor enclosure is the housing that surrounds the coil and contacts, helping to insulate the contactor's key components.
NO and NC contactors are the two types of electrical contactors. NO stands for Normally Open, and NC stands for Normally Closed. This describes the state of a contactor when the voltage in the system is off. A Normally Open (NO) contactor has an open circuit, and no current flows through it. In contrast, a Normally Closed (NC) contactor lets the current flow through the closed circuit in its normal state. In their energised state, they work in the opposite way: the Normally Open (NO) contacts let the current flow through the circuit, while the Normally Closed (NC) contactor stops the current from flowing through the circuit.
NO and NC contactors are available in one unit, and they can be distinguished based on colour. The NC contactor’s plastic cap or label is marked red or pink, as is done with push buttons and emergency stops. This is done intentionally to avoid damage and incidents.
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NC contacts are used to drain energy
An electrical contactor is a device used to switch power to a circuit repeatedly. It is used in situations where power loads need to be turned on and off frequently or rapidly, and for higher power applications than relays. Electrical contacts come in two different states: normally closed (NC) and normally open (NO).
NO contacts, on the other hand, are mostly used in electrical systems where, for safety reasons, you want to be sure that the contactor opens when the power is cut. In a NO contactor, the circuit is established while the contactor is energised and receiving current. When the contactor is de-energised, the contacts are open, and the circuit is off.
It's important to know the difference between NC and NO contacts to determine the correct choice for a specific application. For example, NO contacts are often used in lighting occupancy sensors, equipment cooling systems, and pilot lights. In contrast, NC contacts are used in applications where it is essential to maintain a closed circuit until a voltage drop occurs.
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Frequently asked questions
NO stands for Normally Open. This describes the state of a contactor when the voltage in the system is off.
In a Normally Open configuration, the circuit will only be established while the electromagnet in the contactor is receiving current. When the current stops, the contacts will open, and the circuit will be off.
Normally Open contactors are used in electrical systems where, for safety reasons, you want to ensure that the contactor opens when the power is cut in the system, for example, in the case of a power failure.
When the coil of a Normally Open contactor is energised, the contacts are pushed together, establishing the circuit and allowing power to flow. When the coil is de-energised, the contacts will open, and the circuit will be interrupted.
You can connect an auxiliary or feedback contact to the PLC input to notify you when the contactor is broken. When the contactor is working properly, the feedback contact will be closed, and a signal will be sent to the PLC input.
