Electric Switch

What is a Switch?

Electrical component that can break an electrical circuit, a switch is an electrical component that can disconnect or connect the conducting path in an electrical circuit, interrupting the electric current or diverting it from one conductor to another.

A switch may be operated manually, for example, a light switch or a keyboard button, or may function as a sensing element to sense the position of a machine part, liquid level, pressure, or temperature, such as a thermostat. Many specialized forms exist, such as the toggle switch rotary switch mercury switch push-button reversing switch relay circuit breaker. A switch is an electrical switching apparatus used to make or break an electrical connection, typically completing or breaking contact with at least two electrically conductive paths. The term "contactor" refers specifically to devices which complete or break an electrical circuit, whereas the broader term "electromagnet" includes both types of devices.

The most familiar form of switch is a manually operated electromechanical device with one or more sets of electrical contacts, which are connected to external circuits. A switch may be directly manipulated by a human as a control signal to a system, such as a computer keyboard button, or to control power flow in a circuit, such as a light switch. A switch that is operated by another electrical circuit is called a relay. Practical switches fall short of this ideal; as the result of roughness and oxide films, they exhibit contact resistance, limits on the current and voltage they can handle, finite switching time, etc. Switching devices have been known since ancient times. In modern electronics, there are many different kinds of electronic components that perform similar functions. These include transistors, diodes, resistors, capacitors, inductors, integrated circuits, vacuum tubes, relays, mechanical switches, optical switches, semiconductor junctions, thermionic valves, photocells, piezoelectric crystals, electrochemical cells, and so forth.


In the simplest case, a switch has two conductive pieces, often metal, called contacts, connected to an external circuit, that touch to complete the circuit, and separate to open the circuit. Contact materials are also chosen on the basis of electrical conductivity, hardness, mechanical strength, low cost and low toxicity. Sometimes the contacts are plated noble metals, for their excellent conductivity and resistance to corrosion. The term “contact” refers to one or more parts which make physical connection with another part by touching it. In switches, contacts can be made of various types of materials including: copper, brass, silver-plated steel, gold-plated steel, nickel, stainless steel, aluminum, carbon fiber composite, graphite, molybdenum, tungsten carbide, titanium nitride, silicon carbide, diamond, glass, ceramic, polymers, etc.

Contact terminology

When the contacts are separated by an insulating air gap, they are said to be "open", and no current can flow between them at normal voltages. A contactor is a device consisting of many pairs of metal plates arranged so that they touch each other under certain conditions but do not otherwise make direct connection. This allows control over the connections made through it. Contactor devices are often referred to as relays because they resemble small mechanical relays. They were originally developed for industrial uses, particularly switching large currents; modern versions are designed for household and commercial usage.

Contact bounce

Snapshot of switch bounce on an oscilloscope. Contact bounce is a common problem with mechanical switches and relays, which arises as the result of electrical contact resistance phenomena at interfaces. The effects of contact bounce can be eliminated by use of mercury-wetted contacts, but these are now infrequently used because of the hazards of mercury. Bounce in SPDT switch contacts signals can be filtered out using a SR flip-flop Schmitt trigger. Hammond organ, multiple wires are pressed together under the piano keys of the manuals. A typical example of contact bounce occurs when two metal parts come into physical contact. If they do not touch perfectly flatly, there will always be some amount of force required to make good contact. This means that if you press down hard on your finger against a piece of paper, it takes some effort to get through the paper without leaving any marks behind. Similarly, pressing a button requires some pressure to overcome the friction caused by imperfections in the materials involved.

Arcs and quenching

When the power being switched is sufficiently large, the electron flow across opening switch contacts is sufficient to ionize the air molecules across the tiny gap between the contacts as the switch is opened, forming a gas plasma, also known as an electric arc. For example, the switch contacts may operate in a vacuum, immersed in mineral oil, or in sulfur hexafluoride In AC power service, the current periodically passes through zero; this effect makes it harder to sustain an arc on opening. An electrical circuit that has been interrupted must remain isolated from any source of energy that could cause re-ignition of the arc. This includes not only direct sources such as lightning but also indirect ones like static electricity built up during handling of the equipment. To avoid these problems, all switching devices should include some means to interrupt the arc once formed. There are two basic types: mechanical and magnetic.

Power switching

A power supply or DC/DC converter uses one or more electronic devices called "switches" that are used for controlling electrical energy flow from an input source to an output device such as a light bulb. The most common type of switch used in electronics today is the transistor. Transistors can either conduct electricity directly by allowing electrons to move freely across their terminals, or they can control the amount of current flowing into another component by turning it completely off or fully on.

Incandescent loads

The term “incandescent” refers to any type of light source with a tungsten filament inside it. The most common types are: 1. Incandescents—a general name used by many manufacturers for all lamps using filaments made from tungsten or other refractory metals. These include halogen bulbs, compact fluorescent lights, metal halide lamps, etc.

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