I would say they are a design decision.
I can not think of any section in the NEC that directly requires a shunt trip breaker.
This section is a good example.
645.10 Disconnecting Means.
A means shall be provided to disconnect power to all electronic equipment in the information technology equipment room. There shall also be a similar means to disconnect the power to all dedicated HVAC systems serving the room and cause all required fire/smoke dampers to close. The control for these disconnecting means shall be grouped and identified and shall be readily accessible at the principal exit doors. A single means to control both the electronic equipment and HVAC systems shall be permitted. Where a pushbutton is used as a means to disconnect power, pushing the button in shall disconnect the power.
They do not tell us how to accomplish this but a shunt trip breaker is a common method.
Instead of buying and installing a contactor all you need to do is order a shunt trip kit for the main breaker(s) feeding the space.
I have not seen that application controlled by a computer but they are often controlled by Fire Alarm Systems.
Other areas I have used shunt trips.
1)Commercial Kitchen Equipment, there are codes (Fire?) that require the kitchen equipment under the exhaust hood to be shut down if the fire suppression system is activated.
2)In my area there is still a city that requires buildings to have an outside disconnecting means, they will accept a button outside to trip the main inside.
3)Elevators, we where using shunt trips on elevator feeders to kill the power when a heat detector tripped this was separate and in addition to elevator recall by lobby smoke detectors.
4)Ground fault protection of 277 volt heat trace circuits. We use a 277 volt shunt trip breaker with an external CT donut to provide the required protection.
5)I have not done this but they could certainly be used for load shedding when a generator comes on line that does not have the capacity to run the total load.
In all these cases I believe we could use contactors instead of shunt trip breakers.
But a shunt trip kit in any size is a lot less costly than the cost of a 100, 200, 400 amp 600 volt contactor and installation.
That has been my experience, I am sure others have used them in more applications.
