Utility causes a breaker to trip?

[ElectricPersonality]

*Multiple air handler circuit breakers tripped during a power disturbance when the supply voltage from the utility company dipped well below "normal".
*each circuit breaker is a fixed trip thermal magnetic breaker.
*each air handler is 3 phase.
*I don't believe any of the air handlers have phase failure protection.
*one of the breakers that tripped was a breaker that was integral with the air handler controller. It was used for motor overload protection so it was sized close to the running load amps.
*why would they trip on an undervoltage condition? I thought breakers trip only on short circuits and overcurrent conditions, not on voltage fluctuations? Could a voltage sag cause a current surge in order for the fans to try to maintain rated horsepower, and thus cause the circuit breaker to trip? I would expect the voltage sag would cause the motor contactors to drop out and cut power to the unit entirely.

*There was a report that power was lost to some nearby buildings (within a few miles), and that the utility company had a circuit that had faulted which caused the power loss. The building where the air handlers were located never lost power, just experienced some voltage swings (possibly due to the power company problems).

 

[zog]

They did not trip on UV, unless they have UV protection. And this is why you want to have UV protection.

Your loads are going to fraw the same amount of power regardless of voltage. When voltage drops, the motor (or whatever) will draw more current, tripping your breakers. .

 

[robbietan]

*Multiple air handler circuit breakers tripped during a power disturbance when the supply voltage from the utility company dipped well below "normal".
*each circuit breaker is a fixed trip thermal magnetic breaker.
*each air handler is 3 phase.
*I don't believe any of the air handlers have phase failure protection.
*one of the breakers that tripped was a breaker that was integral with the air handler controller. It was used for motor overload protection so it was sized close to the running load amps.
*why would they trip on an undervoltage condition? I thought breakers trip only on short circuits and overcurrent conditions, not on voltage fluctuations? Could a voltage sag cause a current surge in order for the fans to try to maintain rated horsepower, and thus cause the circuit breaker to trip? I would expect the voltage sag would cause the motor contactors to drop out and cut power to the unit entirely.

*There was a report that power was lost to some nearby buildings (within a few miles), and that the utility company had a circuit that had faulted which caused the power loss. The building where the air handlers were located never lost power, just experienced some voltage swings (possibly due to the power company problems).

it is always a good thing to have phase failure protection if you have 3 phase loads, especially motors

voltage sags can cause motor contactors to drop out and at the same time, trip overcurrent protection devices as well