Shunt Trip Breakers

[BurnetteHoods]

Hello, Ill start by saying i am NOT an electrician. I do own a small business installing commercial kitchen exhaust systems and fire suppression systems. I assist the electrician on site normally in wiring the Fire system and alarms.
I recently heard of a shunt trip breaker.
In the past, and on most jobs, electricians will run the power to outlets behind the hood through a contactor. The contactor stays on ALL THE TIME until my fire system is tripped. The the contactor is released from a micro switch and the power shuts off. So the contactor stays pulled in 24/7. I've thought this cant be good for a contactor. But again...im no electrician.
So would a Shunt Trip Breaker eliminate the need for a contactor? How does a Shunt Trip Breaker work exactly? Can someone explain it in "non-electrician terms" for me? LOL. Could the breaker be wired to a N.C. Micro Switch and then activate when the switch is opened and shut of multiple outlets?

 

[James]

often a shunt trip is an add on unit to a normal breaker, sometimes it is a combined unit.
for small size breakers that are not in the 100’s or 1000’s of amps ratings it is often a fairly simple solenoid that when you apply power to it, will Simpley nudge the breaker to the off or tripped position.
after this has happened, the breaker has to be reset by hand.

I doubt that it is suitable for use as an emergency power off cause it is not fail safe. I.e. if the coil failed, nothing would happen when you tried to trip it remotely.

in comparison, a contactor is considered fail safe by design because if it fails, a spring turns it off and it will stay off until repaired.

 

[Julie.]

Hello, Ill start by saying i am NOT an electrician. I do own a small business installing commercial kitchen exhaust systems and fire suppression systems. I assist the electrician on site normally in wiring the Fire system and alarms.
I recently heard of a shunt trip breaker.
In the past, and on most jobs, electricians will run the power to outlets behind the hood through a contactor. The contactor stays on ALL THE TIME until my fire system is tripped. The the contactor is released from a micro switch and the power shuts off. So the contactor stays pulled in 24/7. I've thought this cant be good for a contactor. But again...im no electrician.
So would a Shunt Trip Breaker eliminate the need for a contactor? How does a Shunt Trip Breaker work exactly? Can someone explain it in "non-electrician terms" for me? LOL. Could the breaker be wired to a N.C. Micro Switch and then activate when the switch is opened and shut of multiple outlets?

As long as the contactor is designed for full time operations, there is no problem with it's use like this - many things are energised 100% of the time, for example your electricity meter, central heating timers etc.

A breaker with Shunt trip operates as follows, the breaker/switch works like any standard switch, when it's closed it is held mechanically by the mechanism itself.
However, there is an additional mechanism which has a solenoid - if power is applied to this solenoid coil it causes the internal mechanism to trip - just like say pressing the "off" lever on the switch.

This coil is known as a Shunt trip coil.

BUT it needs some form of power to operate, and in some circumstances you may not be able to rely on the main supply - for example if the system is short-circuited the voltage goes to zero, so you cannot use this and you either need a battery supply for the protection circuit (overcurrent relay, and Shunt trip coil), or use some other device for the actual protection.

(There are some other ways of doing it involving fuses and special transformers known as current transformers etc)

However if you want to use the Shunt Trip for other actions such as the one you describe - the breaker replaces the contactor, and your control circuit provides a voltage to the trip coil in order to trip the breaker (only to trip) rather than supplying voltage to close (always on) then this is suitable.

However, this is usually not-desirable as the fans will come back on automatically when supply returns in Normal operation and is not regarded as fail-safe since you have to actively stop it.

Rather than the existing case where it automatically stops if the supply to the fire system fails, or the wires of the control circuit are cut.

With a shunt trip if the connection to the coil is forgotten or cut, nothing happens when its supposed to!