Electrical Switches

SKU: C-589Duration: 17 Minutes

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Language:  English

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Course Details


Training Time: 17 minutes

Compatibility: Desktop, Tablet, Phone

Based on: Industry Standards and Best Practices

Languages: English

Switches are an inherently simple technology that we encounter constantly as we move through a day. An electrical switch is a device used to start or stop the flow of electrical current in a circuit. This is accomplished by using some type of actuating force to either bring together or separate a pair of electrical conductors called contacts.

Learning Objectives

  • Describe the purpose of a switch
  • Describe the difference between maintained and momentary switches
  • List the two major categories of switch actuation
  • Explain the term "normally open"
  • Describe "poles" and "throws"
  • Define a limit switch
  • Describe a mercury switch
  • Describe a relay

Key Questions

The following key questions are answered in this module:

What is the difference between a maintained and a momentary switch?
In a maintained switch, the state of the switch is held after each actuation. This describes the typical light wall switch. A momentary switch changes state only for the duration of actuation and then returns to its normal state. This describes the action of doorbell switch.

How can a switch be actuated?
Switches can be actuated by hand, or by any number of external physical forces such as a moving part, or a change in pressure, temperature, liquid level, light level, or position.

What are switch poles and throws?
Poles can be thought of as the number of input terminals to a switch, with throws being the number of output terminals.

What is one advantage common to mercury and reed switches?
In both mercury and reed switches the actual contact action occurs in a sealed (often glass) tube. This means that these types of switches can be safely used in hazardous environments, and both have very long service lives.

What are two classes of switches that not only control the flow of electricity, but are also actuated by electricity?
Electromechanical relays use electricity to create a magnetic field that operates a set of switch contacts. Solid-state devices such as transistors and silicon-controlled rectifiers have the same functionality, but rely on the properties of doped semiconductors to do the actual switching.

Sample Video Transcript

Below is a transcript of the video sample provided for this module:

Limit switches are triggered by the position of a machine part that contacts and actuates the switch. There is a sub-group of conditionally actuated switches that respond to physical conditions such as temperature, pressure, magnetic fields, liquid level, gravity or light. These switches rely on some type of transformational mechanism to sense a condition and convert that into a switch actuation. The transformational mechanism is often integrated into the switch. For example, a bimetallic strip consists of two strips of dissimilar metals bonded together that bend as the temperature changes. The bending motion can be combined with a switch to turn a furnace on and off, thereby creating a thermostat that can be used to control the temperature of a house. A change in pressure in a compressed air tank can be move a piston or diaphragm that can, in turn, operate a switch to turn a compressor on and off to maintain a given air pressure range in the tank.

Additional Resources

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