Shunt trip

Status
Not open for further replies.
A shunt trip operates much like a lighting contactor in reverse. But instead of energizing a coil to engage contacts, a shunt trip engages a circuit to open the overcurrent or switching device.
 
A shunt trip CB is an electro-mechanical device that opens either when voltage is applied or removed from the shunt coil. Think of it as a CB operating normally with the ability to be opened by using the mechanical coil within the breaker. This allows the breaker to open from a remote source typically an EPO, F/A pre-action or an Ansul system.
 
A shunt trip (ST) is a simple solenoid. Apply power to the coil the plunger extends, hits the trip bar in the breaker and the breaker trips. Most common shunt trips also have a cut-off switch that is N/C and is an integral part of the ST assembly when the shunt trip has not been activated. When power is applied to the ST, the plunger extends and hits the trip bar, either the trip mechanism or one of the moving contacts itself with either push a button on the N/C contact or move a lever that pushes that button which immediately opens that contact and removes power from the shunt trip coil.
Because the ST coil draws a significant amount of current it is omerative that the power be removed from it immediately after it is actived to prevent the coil from being fried.
The other type of tripping devide is an under voltage release (UVR) which must be energized before the breaker is closed and when the breaker is closed. Remove the power from the UVR and the breaker trips instantly.
The is a 3rd method of tripping a breaker remotely and that's with a flux transfer shunt trip which would take a much lengthier explanation as to how it operates and why it would be used.
 
Something to think about with a shunt trip is that they are not failsafe. Meaning if used for life safety applications they do not fail in the tripped state. As others have said, you have to supply power from another circuit to trip the breaker.

Many times these are used to comply with codes to shut down underhood appliances when an ansul type system goes off. The problem is is that if you turn off the the breaker that supplies the control circuit, now your under hood appliances don't trip. I work with one AHJ that will not allow shunt trip breakers for under hood equipment shutdown.
 
I work with one AHJ that will not allow shunt trip breakers for under hood equipment shutdown.
Click to expand...

What gives him the right to do this, what about a fuse or CB for a switchboards GFP protection, how does he stop workers from shutting off this vital level of protection. One can not account for all levels of incompetence.
 
I much prefer to use an Undervoltage Release mechanism instead of a Shunt Trip mechanism. That way if power is lost, the breaker trips. I am uncomfortable with not being able to trip the breaker because of a power loss, broken wire, open fuse, hungry rat, out of control forklift, etc etc.
 
kc8dxx said:
I much prefer to use an Undervoltage Release mechanism instead of a Shunt Trip mechanism. That way if power is lost, the breaker trips. I am uncomfortable with not being able to trip the breaker because of a power loss, broken wire, open fuse, hungry rat, out of control forklift, etc etc.
Click to expand...

I'm not sure you would want to do that with an elevator though. (Thats the most common application I see for shunt trip breakers.)

Steve
 
steve66 said:
I'm not sure you would want to do that with an elevator though. (Thats the most common application I see for shunt trip breakers.)

Steve
Click to expand...

Steve, I'm curious (I never worked on an elevator), how is a shunt trip used in an elevator circuit/control?

I've mostly seen them (shunt trips) in kitchens and gas stations for E-stops (I don't like them for the same reason you responed to).
 
sceepe said:
I work with one AHJ that will not allow shunt trip breakers for under hood equipment shutdown.
Click to expand...
brian john said:
What gives him the right to do this
Click to expand...

Selecting series or shunt EPO is an area that has many shades of gray, but generally, for worker protection where there is a reasonable likelihood of the dangerous event occuring, series beats shunt every time, simply on the basis that it fails safe.

In my book, that inspector has made a good call. He may not have the "right", but long may he continue.
 
dbuckley said:
In my book, that inspector has made a good call. He may not have the "right", but long may he continue.
Click to expand...

I think I have run into this guy before - or one of his apostels. Only had to swap two breakers and all the NC/NO's, but if it were too many more CB's I might have questioned it more.
 
Lou,
Steve, I'm curious (I never worked on an elevator), how is a shunt trip used in an elevator circuit/control
Click to expand...
The shunt trip signal comes from the fire alarm master controller, however you can not tie this signal directly to the shunt trip device, since most shunt trip devices require more amperage to trip, than the shunt trip signal can deliver. The end result is you will burn out the shunt trip module within the fire alarm controller.
 
davidr43229 said:
The shunt trip signal comes from the fire alarm master controller, ..
Click to expand...

So can I infur the fire alarm system shuts down the power to the elevators? Then someone has to reset them (shunt trip breakers) manually?

What if there are people actually using the elevator? Are there battery backups to power the elevator to the nearest floor? Are the people just stuck between floors? What if the fire fighters wanted to recall an elevator?

I feel like a 6-year old asking "why?".
 
So can I infur the fire alarm system shuts down the power to the elevators? Then someone has to reset them (shunt trip breakers) manually?

What if there are people actually using the elevator? Are there battery backups to power the elevator to the nearest floor? Are the people just stuck between floors? What if the fire fighters wanted to recall an elevator
Click to expand...
The Shunt trip signal is sent only after a heat or smoke detectors hit a certain threshold and the elevator hits a home floor recall.
This type of device if not allowed in Michigan and other states, where they have fire rated doors, for a min of 2-3 hours for fire fighters to use.
In the case of firemen, when the shunt trip actuates, they have to use the stairs.
Sorry it took me so long to reply.
 
As previously described shunt trips trip the breaker in a similar fashion as if they tripped automatically. They have to be reset and closed. However, if the ST circuit happens to be still energized the breaker will immediately trip again when the breaker is closed again and the cut-off switch in series with the ST circuit closes.
The undervoltage release, on the otherhand, trips the breaker when power is taken away from it. Hoowever, it must be energize before any attempt is made to reset and close the breaker.
Another means of tri[pping a breaker is with a flux transfer shunt trip used in combination with a capacitive trip device. The flux transfer shunt trip takes very little energy to release it and the capacive trip devide is a capacitor which stores power for a brief period of time. If control power is lost the capacitive trip device store enough energy that can be used and discharged into the flux transfer shunt trip with is somple contact closure.
The flux transfer shunt trip can be relatched by simply resetting and closing the breaker without control power present.
 
Status
Not open for further replies.
Top