How to Distinguish between Normally Open and Normally Closed Contacts of a Contactor

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The following are several methods for distinguishing between normally open and normally closed contacts of a contactor:

Distinguish According to the Definition

- **Normally Open Contacts**: When the contactor is not energized, the contacts are in an open state, that is, the circuit is in an open state. When the contactor is energized, the coil generates a magnetic field, attracting the contacts to close and realizing the connection of the circuit.

- **Normally Closed Contacts**: When the contactor is not energized, the contacts are in a closed state, that is, the circuit is in a connected state. When the contactor is energized, the coil generates a magnetic field, causing the contacts to open and realizing the disconnection of the circuit.

Distinguish by Symbols

- **Normally Open Contacts**: They are usually represented by a contact symbol without a small circle. In an electrical schematic diagram, a normally open contact is represented by a rectangle with a small dot. The small dot represents that the contact is open when not energized.

- **Normally Closed Contacts**: They are usually represented by a contact symbol with a small circle and a dot inside the circle. In an electrical schematic diagram, a normally closed contact is represented by a rectangle without a small dot, indicating that the contact is closed when not energized.

Distinguish from the Structural Appearance Observe the contact part of the contactor. The moving contact and the stationary contact of a normally open contact are separated when not energized, and there is an obvious gap between them. While the moving contact and the stationary contact of a normally closed contact are in contact with each other when not energized, showing a closed state.

Distinguish According to Functions and Application Scenarios

- **Normally Open Contacts**: They are often used to control the on-off of circuits and realize functions such as starting or stopping equipment. For example, in a motor starting circuit, a normally open contact can be used to connect the power supply of the motor to make the motor start running. When the contactor is energized, the normally open contact closes, the circuit is conducted, and the equipment starts to work.

- **Normally Closed Contacts**: They are often used in scenarios such as safety protection and emergency shutdown. For example, in the case of equipment failure or abnormal conditions, a normally closed contact can quickly cut off the power supply to protect the safety of equipment and personnel. When the contactor is energized, the normally closed contact opens and cuts off the relevant circuit.