A fault on a branch circuit resulted in tripping the 1,200A feeder breaker, but the 200A branch circuit breaker did not trip. The 200A breaker was replaced with a new one.
One of the maintenance electricians suggested there might be a problem with the 1,200A breaker. Since the 200A one has already been pulled, testing it first won’t incur any downtime. So, he suggested sending the 200A breaker out for testing, to rule it out as the culprit.
Thus, the breaker was sent to a local electrical shop that just happened to own a breaker testing device. Various levels of overcurrent were used to test the breaker, and it opened each time. Should you send the shop the 1,200A breaker to see what it does?
The response to this situation indicates a breaker coordination study has not been performed. That’s a bigger issue than simply solving this one conflict.
Determine the time delay of each breaker. Then have that electrical shop test the 200A one against the specified time delay, not just whether the breaker trips. The 200A breaker might have responded slowly due to poor maintenance (e.g., improper cleaning and lubrication). What is the maintenance history of that breaker? If there isn’t any, that is also a bigger issue.
Check the bonding connections of that 200A circuit. And if you have either of the other two problems, contact a qualified firm for help.