Don't touch that dial... with maintenance of vintage molded case breakers. or lack thereof, being the elephant in the room when it comes to the reliability of many AF Hazard analyses and spawning lengthy disclaimers...I am interested in you all's thoughts / experience with adjusting instantaneous trip settings on similarly untested/unmaintained molded case (MCCB) breakers (to improve coordination or reduce AF clearing time and lower IE).

I am thinking that if we shouldn't trust an unmaintained and untested breaker to follow the manf's published clearing times, then we shouldn't trust adjustments made to a 20 year old untested/unmaintained breaker settings...and need to proceed cautiously in recommending setting changes to unmaintained breakers.... Seems like a crap shoot.

Are the reliability of MCCB (thermal mag and electronic) trip setting adjustments well into a breaker's expected life hearty... or is the trip setting mechanism (particularly instantaneous) affected by age, lack of exercising etc?

Curious as to what you think.

I haven't encountered any issues changing instantaneous trip on older MCCB's in the field. Typically done when replacing buckets with spares which had been previously used on lower HP motors and trip setting had to be increased. Some of those were over 30 years old in which starter contacts had been replaced many times.

Bumping this question. I have had the same concern.

Too funny. Just noticed i was the OP/original poster.

Not an MCCB but, humorous a few decades later...

In the 90's I was raising the instantaneous of a first generation electronic trip breaker (not mentioning manufacturer) due to setting changes from a coordination study.

The circuit breaker tripped when RAISING the setting. It turns out there was a design glitch and when the setting was changed from one setting to the next it would drop to zero in between. OOPS*

*undocumented feature.

It was quickly resolved by the manufacturer.

We always put the disclaimer that breakers should be tested to ensure proper trip functions especially if the change is being made to reduce AFIE.

Thermal magnetic breakers are not known to experience aging issues with the calibration of their trip units. Their most common problem seems to be the migration of lubrication of the actual operating mechanism, which can be mitigated by simply cycling the breaker On and Off yearly.

Electronic trip molded case breakers have been known experience aging issues with the calibration of their trip units. These should be tested per their manufacturer's recommendations

Larger drawout style power circuit breakers require regular maintenance and testing.

Of course you will always be able to find examples of outlier situations.