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 Post subject: adjusting Inst. setting on untested/unmainained MCCB's.
PostPosted: Sun Jun 27, 2021 6:48 am 

Joined: Tue Nov 04, 2014 5:53 am
Posts: 16
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.


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 Post subject: Re: adjusting Inst. setting on untested/unmainained MCCB's.
PostPosted: Mon Jun 28, 2021 8:08 am 
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Joined: Mon Jun 11, 2018 12:02 pm
Posts: 15
Location: Slave Lake, Alberta
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.


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