I forgot, smaller size breakers you have to buy as shunt trip breakers, larger frame size breakers you can often buy the shunt trip as an accessory.

If you do field install the shunt unit I recommend doing it in a clean and swept area, there are a lot of small screws, springs and small pieces to get lost when you open up breakers. [Linked Image]

Bob Badger
Construction & Maintenance Electrician
Massachusetts