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Home / Technical Articles / Want to learn to analyze electrical schematics? Great! But first, you must understand these.

Switches and Contacts Essentials

This technical article delves into a diverse array of switches and components that are fundamental to the operation and control of electrical systems. Starting with the basics like TURN, PULL, and PUSH switches, we navigate through the intricacies of latching switches and emergency stop switches, exploring their applications and functionalities in various contexts.

Want to learn to analyze electrical schematics? Great! But first, you must understand these.
Want to learn to analyze electrical schematics? Great! But first, you must understand these. (photo credit: EEP)

As we progress, the article unfolds the concept of Passing Contacts and the unique characteristics of Normally-Open, Timed-Closed, and Normally-Open, Timed-Open Contacts, shedding light on their importance in specific control scenarios.

The transformative role of solenoids in converting electrical energy into mechanical motion is also explored, showcasing their versatility in modern control systems.

Furthermore, the article explores the practical aspects of Change over Contacts, Binary Inputs, and AC Sockets, providing insights into their applications and key features. The concept of Gang Operation of MCB or Circuit Breaker in Schematics is introduced, highlighting its significance in managing electrical circuits efficiently.

In the latter sections, the focus shifts to more advanced components such as CAM-operated change-over switches, Terminals with fuses, and Multi-pin connectors (male and female). The detailed exploration of the Harting Plug, a connector vital in gas-insulated substations, serves as a culmination of our journey through the realm of electrical switches and components.

Ok, so let’s dive into details!

Table of Contents:

  1. TURN Switch
  2. PULL Switch
  3. PUSH Switch
  4. Latching Switch
  5. Emergency Stop Switch
  6. Passing Contacts
  7. Normally-Open, Timed-Closed Contact
  8. Normally-Open, Timed-Open Contact
  9. Solenoids: Transforming Electrical Energy into Mechanical Motion
  10. Change-Over Contact
  11. Binary Inputs
  12. AC Socket
  13. Gang Operation of MCB or Circuit Breaker in Schematics
  14. CAM Operated Change Over Switch
  15. Terminal With Fuse
  16. Multi-Pin Connector Male and Female
  17. Harting Plug

1. TURN Switch

A TURN switch, also known as a rotary switch, is a type of switch that operates by rotating a control knob. It is commonly used to select between different positions or settings in a circuit. The switch typically has multiple contact points arranged in a circular or semi-circular pattern. As the knob is turned, the movable contact arm makes contact with different fixed contacts, thereby establishing or breaking electrical connections.

In a schematic diagram, a TURN switch is represented by a circle with an arrow indicating the rotational direction. The number of positions and the specific connections associated with each position are detailed in the schematic symbols.

Figure 1 – Representation of the turn switch contacts in schematics

Representation of the turn switch contacts in schematics
Figure 1 – Representation of the turn switch contacts in schematics

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2. PULL Switch

A PULL switch is a type of switch that is activated by pulling or tugging on a control mechanism. These switches are often used in devices where a direct and manual action is required to toggle the switch between its ON and OFF states. PULL switches are commonly found in applications like lamps, ceiling fans, or simple devices where a physical pull or tug is convenient for user interaction.

In a schematic diagram, a PULL switch is typically represented by a rectangle or another shape with an arrow or a line indicating the direction of the pull. The switch’s states (ON or OFF) and the associated circuit connections are specified within the symbol.

PULL switches might also have additional features, such as multiple positions or intermediate states, depending on the design and intended functionality.

Figure 2 – Pull button (left) and switch (right) with normally closed contact

Pull button (left) and switch (right) with normally closed contact
Figure 2 – Pull button (left) and switch (right) with normally closed contact

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3. PUSH Switch

A PUSH switch, also known as a momentary switch, is a type of switch that is designed to make or break a connection temporarily when pressure is applied to its actuator. Unlike toggle switches that have a latching mechanism, a PUSH switch returns to its original state when the force is released.

These switches are commonly used in applications where a brief and momentary action is required, such as in push-button controls, doorbells, or as the activation switch for electronic devices.

In a schematic diagram, a PUSH switch is typically represented by a rectangle or another shape with an arrow or line indicating the direction of the push. The symbol reflects its momentary nature, with the switch returning to its default position once the force is no longer applied.

PUSH switches can come in various configurations, including normally open (NO) or normally closed (NC), depending on whether the switch’s default state is open or closed, respectively.

The specific functionality of the switch in a circuit is detailed in the schematic symbol.

Figure 3 – Representation of push button with normally closed contact in schematics

Representation of push button with normally closed contact in schematics
Figure 3 – Representation of push button with normally closed contact in schematics

Figure 4 – Representation of push button with normally open contact in schematics

Representation of push button with normally open contact in schematics
Figure 4 – Representation of push button with normally open contact in schematics

Figure 5 – Push button with key and normally closed contact

Push button with key and normally closed contact
Figure 5 – Push button with key and normally closed contact

Figure 6 – NFPA Symbol representation of the push button with normally closed contact

NFPA Symbol representation of the push button with normally closed contact
Figure 6 – NFPA Symbol representation of the push button with normally closed contact

Figure 7 – NFPA Symbol representation of the normally open contact

NFPA Symbol representation of the normally open contact
Figure 7 – NFPA Symbol representation of the normally open contact

Figure 8 – NFPA Symbol representation of the normally closed contact

NFPA Symbol representation of the normally closed contact
Figure 8 – NFPA Symbol representation of the normally closed contact

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4. Latching Switch

A LATCH switch, also known as a toggle or flip-flop switch, is a type of switch that maintains its state (either ON or OFF) after being toggled until explicitly changed. Unlike momentary switches, which return to their default state when the force is released, latch switches retain their position until another action is taken.

These switches are commonly used in applications where a stable and persistent state is required, such as power controls in electronic devices, light switches, or any scenario where maintaining a specific state is crucial. In a schematic diagram, a LATCH switch is typically represented by a rectangle or another shape with a distinctive toggled arrow or line indicating its toggle action.

The symbol reflects the switch’s ability to “latch” into a position until the opposite action is applied. LATCH switches often have two stable states: one for ON and one for OFF. The switch can be toggled between these states through physical manipulation or electronic signals.

Variations of latch switches include those with momentary actions to set or reset the latch, and they may have multiple poles and throws to control multiple circuits simultaneously.

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Muhammad Kashif - Author at EEP-Electrical Engineering Portal

Muhammad Kashif

Muhammad Kashif Shamshad is an Electrical Engineer and has more than 17 years of experience in operation & maintenance, erection, testing project management, consultancy, supervision, and commissioning of Power Plant, GIS, and AIS high voltage substations ranging up to 500 kV HVAC & ±660kV HVDC more than ten years experience is with Siemens Saudi Arabia.
Profile: Muhammad Kashif

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