Electrical Switching Devices: Types and Functions

Electrical Switching Devices and Components

Switching Device Definitions

Manual Switches

Manual Switches: A switching device with the capacity to interrupt or complete a circuit while under load.

Simple Switch

Switch: A switching device that opens and closes circuits without breaking them in a vacuum. Its primary function is to isolate a section of the power supply wiring to facilitate repairs and maintenance.

Circuit Breakers

Circuit Breaker: A switching device whose main function is to open a circuit under abnormal conditions (such as overload or short circuit). Note: They are often misused to manually disconnect loads.

Circuit breakers are also used as protection devices against indirect contact related to grounding. They shut down the system before a ground leakage current can become dangerous, especially if it flows through a human body during direct contact.

Thermal Relays

Thermal Relay: These protective devices operate based on temperature. Their action relies on the expansion of a bimetallic strip, which dilates to open or close a circuit.

Contactors

Contactor: A remote control switch that returns to its resting position when the driving force is removed. Its main use is for opening and closing circuits related to electric motors.

Elements of a Contactor

The contactor comprises several key elements:

• Electromagnet: Consists of a magnetic circuit and a coil.
• Primary Contacts: Elements responsible for establishing and securing the current flow.
• Auxiliary Contacts: These elements are part of the auxiliary circuit, used for signaling, interlocking, and feedback control.
• Chassis: The structure upon which the contactor's components are mounted.

Key Personnel (Contact Points) Properties

Key Personnel (Contact Points): These are the parts subjected to the hardest work. They are responsible for closing the power circuit or facilitating the connection between the source and the receiver. To perform this task effectively, they must meet specific mechanical and electrical properties:

1. High electrical and thermal conductivity.
2. Low contact resistance.
3. Resistance to being welded or glued shut.
4. Good resistance to erosion caused by electric arcs.
5. High hardness and strong mechanical strength.
6. A low tendency to form electrically resistant acids or sulfides.