Switch

Understanding Switches in Electrical Engineering

In electrical engineering, a switch is an essential component that acts like a gatekeeper for electricity. It’s the silent hero behind countless electronic gadgets and systems, allowing or blocking current flow with its simple yet powerful design.

The Common Electromechanical Switch

Imagine a switch as a door to your house; it either lets you in (closed) or keeps you out (open). The most common type of switch is an electromechanical device, consisting of one or more sets of movable electrical contacts. These contacts connect and disconnect from external circuits, much like how a key turns a lock.

Types and Configurations

Switches come in many flavors, each designed for specific tasks. From toggle switches to rotary switches, mercury switches, push-button switches, reversing switches, relays, and circuit breakers, the variety is vast. Each type has its unique configuration, making it perfect for different applications.

Pole and Throw

When discussing switch contact variations, terms like ‘pole’ and ‘throw’ come into play. A pole refers to the number of electrically separate switches controlled by a single physical actuator. Throws indicate how many positions or states each pole can have. For instance, an SPST (Single-Pole Single-Throw) switch has one set of contacts that can be either open or closed.

Changeover Switches

In a changeover switch, the contacts remain in one state unless actuated. These switches are classified as normally open (NO) or normally closed (NC). A changeover switch combines both types, offering more flexibility and functionality.

Switching Power: The Challenges

When it comes to switching power, things get a bit tricky. Contact bounce is a common issue where the rapidly pulsed electric current occurs due to the elasticity of metal contacts. To combat this, various methods like mercury-wetted contacts or low-pass filtering are employed.

Contact Resistance and Arcing

Practical switches have limitations such as contact resistance and finite switching time. When opening a switch, an electric arc can form, causing potential damage to the switch and generating electromagnetic interference. Fast-moving mechanisms and quenching methods help mitigate these issues.

Switches in AC vs DC Circuits

The behavior of switches differs between AC (Alternating Current) and DC (Direct Current) circuits. In AC service, the current passing through zero makes it harder to sustain an arc on opening. This is why manufacturers rate switches with lower voltage or current ratings when used in DC circuits.

Power Switches: Types and Considerations

Power switches come in various types such as momentary, regular on-off, and dual-action. They are designed to handle the transitional state and operating currents for power switching. Additionally, switches for inductive loads require special ratings to manage spark and electromagnetic interference.

Actuators: The Moving Parts

The actuator is the moving part that applies force to the contacts. It can be a toggle, dolly, rocker, or push-button mechanism. These actuators ensure smooth transitions between states, making the switch user-friendly and reliable.

Biased Switches: Maintaining Position

Biased switches maintain their position once operated. They contain mechanisms to spring into another position when released. Examples include momentary push-button switches, which are either normally open (push-to-make) or normally closed (push-to-break).

Rotary Switches: Multiple Positions and Levels

A rotary switch operates with a twisting motion of an operating handle. It can control multiple circuits simultaneously and often includes detents to hold positions when released. The design allows for multiple poles, providing flexibility in applications.

Knife Switches: A Historical Perspective

Knife switches are simple yet robust devices used in various applications. They consist of a flat metal blade hinged at one end and an insulating handle. When closed, current flows through the blade and fixed contact. These switches can be made in different sizes to carry varying amperages.

DPDT Switches: Dual-Pole Double-Throw

A DPDT (Double-Pole Double-Throw) switch has six connections but some variations are internally wired for polarity reversal with four terminals. These crossover switches can be used as intermediate switches in multiway switching systems, offering versatile control options.

Light Switches: Controlling Your Space

Light switches are ubiquitous fixtures that control lighting and other circuits. By using multiple-pole switches, you can achieve multiway switching control from two or more locations. Slide switches offer a simple yet effective way to toggle between states.

Solid State Switches: The Future of Switching

The term ‘switch’ has expanded beyond its mechanical roots to include solid-state electronics that perform switching functions electronically by active devices. These modern switches are faster, more reliable, and offer a wide range of applications in digital circuits.

In conclusion, switches are the unsung heroes of electrical engineering. From simple toggle and rotary switches to complex relays and circuit breakers, they play a crucial role in controlling and managing electricity. As technology advances, so too do our understanding and applications of these versatile components.