Questionable Breakers?

Status
Not open for further replies.

under8ed

Senior Member
Two recently encountered events with breakers are worth sharing. A thermal scan performed by a contractor found a very hot phase on a newer, very respectable brand breaker. It is a large frame style, believe it to be a 400 amp. We were able to shut down the system & check terminations, but no problems were identified. When we put all back online, the problem had disappeared. I speculated that the breaker contacts may not have seated perfectly as it was likely only cycled on one time since installation. About a week later, production maintenance called us on a panel that had lost a phase since the 3 phase loads dropped. After finding the feed intact, I realized the voltage was dropping through the panel main breaker. Remembering the former event, and knowing this was also a recent installation, same respectable brand, & had only been cycled on once at the time of energizing. Sure enough, when I switched it off & on a couple of times; the problem was gone. Both breakers are being monitored, and are deemed questionable. I am curious if anyone else has run across similar problems; and if not, it may be helpful to share this.
 

Cow

Senior Member
Location
Eastern Oregon
Occupation
Electrician
I haven't come across anything like that, but why not tell use what kind of breaker so we know what to look out for?
 

JRW 70

Senior Member
Location
Eastern Central Missouri
Occupation
Testing and Engineer
Intermittent Breakers

Intermittent Breakers

Yes, I have had "good" breakers not set properly. If this is not
an old installation see if the manuf. will assist. A 400A frame
should not be considered a disposable item in my opinion.
Best of luck in finding a mutually agreeable solution.

Jimmie
 

Jraef

Moderator, OTD
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
NFPA 70B recommends that MCCBs (Molded Case Circuit Breakers) should be exercised, meaning turned off and on a couple of times, once every 6 months or so. The contacts build up an oxidation layer or film which eventually can lead to increased resistance, then heat. When the contacts open and close, they are designed to "wipe" across each other to help remove any film buildup.

Nobody does it of course, but it is recommended. That at least explains why it goes away. Before the advent of low cost thermal scanners, hardly anyone knew it was happening and the breakers survived for years without noticeable damage. Now more people can see what's really going on.
 

under8ed

Senior Member
I haven't come across anything like that, but why not tell use what kind of breaker so we know what to look out for?

I really didn't want to bad mouth our favored brand, I think many electricians feel that Square D is the "Klein" of electrical equipment. Now that I have been educated on the fact that we have not been following the recommended practices of "exercising" the devices: I feel better about naming the brand.
 

Galt

Senior Member
Location
Wis.
Occupation
master electrician and refrigeration service tech.
Probably not it but in the past few years we have had trouble with Japanese beatles crawling into breakers and causing similar problems.
 

qcroanoke

Sometimes I don't know if I'm the boxer or the bag
Location
Roanoke, VA.
Occupation
Sorta retired........
Nah, it's just Paul's left handed bass that causes the problem, that's why you don't see it happening more often, most other Japanese bass playing beatles use right handed basses.

And if they're left handed that just string it backwards like Hendrix.
 

templdl

Senior Member
Location
Wisconsin
But seriously as stated previously contacts do rub together when they close and if heating is experienced over and above the natural heating that is expected exercising a breaker should!d reduce or solve that issue.
Since the line end terminals are closer to the contacts that line side terminals of the contacts in question should also indicate heat. Also remember that if a breaker has a physically bimetalic trip unit the beast generated by those contacts should also heat the thermal elements and derate the breaker which may cause nuisance tripping.
BUT, remember the heat generated by the contacts in question can weaken the springs that hold the contacts closed which will cause the heating issue to escalate.
As such one should seriously consider replacing the breaker.
 
Status
Not open for further replies.
Top