Switching 3-Phase Circuits: How To, Relays & Push Buttons

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Discussion Overview

The discussion revolves around the methods for switching 3-phase circuits on and off, particularly in industrial settings. Participants explore the use of relays, contactors, and mechanical switches, as well as the implications of switching all three phases simultaneously.

Discussion Character

  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions whether it is possible to switch just one leg of a 3-phase circuit or if all three must be switched simultaneously.
  • Another participant asserts that all three phases need to be switched at once, noting that industrial applications typically use electronic switches rather than simple mechanical ones.
  • A third participant mentions the use of a 3-phase relay or contactor as a solution for switching, providing a link for further information.
  • One participant describes the existence of mechanically linked single pole switches that can be used to switch all three phases together, including the use of circuit breakers with a peg mechanism.
  • Another participant references high-voltage circuit breakers used in electrical power transmission networks as a method of control and protection.

Areas of Agreement / Disagreement

Participants express differing views on whether it is acceptable to switch only one phase of a 3-phase circuit, with some asserting the necessity of switching all three simultaneously. The discussion remains unresolved regarding the best practices for switching methods.

Contextual Notes

Some participants reference specific types of switches and circuit breakers, but there is no consensus on the optimal approach or the technical requirements for switching 3-phase circuits.

triden
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Hello,

How do you switch a 3-phase circuit on and off? Is it possible to put a relay on just one leg of the phase, or do you need to somehow switch all 3 at the same time? In industry, what do they use to switch 3-phase circuits, for instance, with a push button start/stop?

Christan
 
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You definitely need to switch all three at once.
since three phase is generally used with failry beefy supplies you tend to have a controller switching them from an electronic switch rather than a simple mechanical switch.
 
triden said:
Hello,

How do you switch a 3-phase circuit on and off? Is it possible to put a relay on just one leg of the phase, or do you need to somehow switch all 3 at the same time? In industry, what do they use to switch 3-phase circuits, for instance, with a push button start/stop?

Christan

A 3-phase relay or contactor: http://www.allaboutcircuits.com/vol_4/chpt_5/2.html

CS
 
You weren't very specific, triden, but there are plenty of switches out there that are simply three single pole switches mechanically linked together. Any ordinary circuit breaker can have a peg inserted between it and its neighbors to make such a switch, for example. Larger ones are specially made with 3 poles, but function the same. You can get relatively ordinary circuit breakers probably up to a few thousand amps at a few thousand volts. Grainger stocks them up to 1000A at 600V.
 
Last edited:

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