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

[triden]

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

 

[mgb_phys]

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.

 

[stewartcs]

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

 

[russ_watters]

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.

 

[dlgoff]

Electrical power transmission networks are protected and controlled by high-voltage breakers.

http://en.wikipedia.org/wiki/Circuit_breakers#High-voltage_circuit_breakers"