In a new building, during storms, the Shunt Trip breakers in the building all trip. What can be causing this? Is Transient Voltage a possiblity? Are these shunt trip breakers so sensitive that a transient voltage could cause them to trip? And can you set the sensitivity of a shunt trip breaker? I understand how a shunt trip breaker works, but I am not clear on the inner workings of the breaker and how it integrates with the shunt trip device inside the breaker. Also, most of the breakers are not controlled by an EPO, but rather a refrigerant leak monitor for the chiller room. Others are controlled by an EPO, but seem to trip much less.
Shunt Trip Sensitivity
- Thread starter ESMD
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- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
The Shunt Trip does not alter the functioning of the breaker, all it does is mechanically hit the breaker's normal trip mechanism, the same as if it were the thermal trip or the magnetic trip elements. It just does so only when it gets a "signal" to do so from an external source.
So sure, from that standpoint, a big enough "transient" on that external source would energize the coils and they would trip the breakers. I'd be hunting for a different source of trouble however, transients that big would likely be doing other obvious damage. I'd be looking for a crossed wire somewhere, or some kind of glitch in the EPO or Refrigerant leak system that is wired to the Shunt Trip Coils. You could attach a recorder to the coil circuits and see what other kinds of events are happening when the circuit gets energize, that's usually a great way to find things like that.
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
You might try temorarily disconnecting the trip conductor of one (or more), and see if that breaker(s) stops tripping,
There is the common shunt trip which uses a solenoid to strike the trip bar and then there is the flux transfer shunt trip which is held in place with a magnet compressing a spring and released to trip the breaker with very low lever AC current messes up the magnets ability to hold the tripping mechanism in place. The spring is allowed to decompress causing the mechanism to hit the trip bar.
It is unlikely that a standard shunt trip would trip in the manor that you describe but I could see a flux transfer shunt trip tripping from a voltage transient because they are much more sensitive.
My suggestion would be to identify the type of shunt trip that you have.
One thing that may solve a nuisance tripping problem is to load the circuit with a small resistor in parallel with the circuit. The resistor would bleed off any unwanted voltage that may occur is rare occasions but would not affect the shut trips operation when it is legitimately energized. But a word of caution would be that you probably want to remove the voltage from the trip circuit immediately after a trip because you may end up frying the resistor.
Remember that with a flux transfer shunt trip the only needs to be enough current to weaken the magnet's flux which allows the spring to expand allowing the mechanism to extent and hit the trip bar of the breaker.
It is unlikely that a standard shunt trip would trip in the manor that you describe but I could see a flux transfer shunt trip tripping from a voltage transient because they are much more sensitive.
My suggestion would be to identify the type of shunt trip that you have.
One thing that may solve a nuisance tripping problem is to load the circuit with a small resistor in parallel with the circuit. The resistor would bleed off any unwanted voltage that may occur is rare occasions but would not affect the shut trips operation when it is legitimately energized. But a word of caution would be that you probably want to remove the voltage from the trip circuit immediately after a trip because you may end up frying the resistor.
Remember that with a flux transfer shunt trip the only needs to be enough current to weaken the magnet's flux which allows the spring to expand allowing the mechanism to extent and hit the trip bar of the breaker.
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
These are usually used with a control device that 'creates a trip signal, such as a Ground Fault system. Rarely, if ever, are flux transfer devices used with a standard contact and voltage source. But it does pay to know what you actually have.
weressl
Esteemed Member
To follow your idea, ground faults are set at a much lower level than phase currents, especially in resistance grounded systems and if there is no appreciable time delay, surge traveling to ground could trip the GFP/Solenoid.
My point was that if you did consider the voltage required to activate a common solenoid operated shunt trip where would one get enough stray, inducted, or other voltage backed by enough current to cause a shunt trip to function. That's why I pointed out the flux transfer shunt trip which would be much more susceptible to such a phenomenon.
Typically, a Cutler-Hammer 120vac rated ST for an F, J, and K frame breakers require any where for 84-120va to operate. They are able to function at minimum voltage of 60vac with 100-120va.
Remember that shunt trips do have an integral cut off switch build in to the circuit which immediately opens the circuit removing power from the shunt trip after it is activated.
As such it can operate over a wide voltage range without sustaining any damage from the higher voltages within their operating range.
But when you consider the va required to activate the shunt trip where could that power come from to cause the ST to nuisance trip?
Typically, a Cutler-Hammer 120vac rated ST for an F, J, and K frame breakers require any where for 84-120va to operate. They are able to function at minimum voltage of 60vac with 100-120va.
Remember that shunt trips do have an integral cut off switch build in to the circuit which immediately opens the circuit removing power from the shunt trip after it is activated.
As such it can operate over a wide voltage range without sustaining any damage from the higher voltages within their operating range.
But when you consider the va required to activate the shunt trip where could that power come from to cause the ST to nuisance trip?
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