250 amp breaker

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iaov

iaov

Senior Member
Location
Rhinelander WI
Was called in to a small industrial plant where a 250A breaker tripped as the result of a phase to phase fault. I was told that this was the second time a fault had occured on this breaker and the client wants to relace the breaker. My question is "Is replacing this breaker necessary?" Will appreciate your opinions.
 
zog

zog

Senior Member
Location
Charlotte, NC
iaov said:
Was called in to a small industrial plant where a 250A breaker tripped as the result of a phase to phase fault. I was told that this was the second time a fault had occured on this breaker and the client wants to relace the breaker. My question is "Is replacing this breaker necessary?" Will appreciate your opinions.
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Sounds to me like the breaker is doing it job just fine. Have you (or anyone) tested it? Could be a faulty trip unit (I assume this has a digital trip unit since you stated the type of trip was known). Or maybe, just maybe there is a fault?!? Any testing done on the system?
 
iaov

iaov

Senior Member
Location
Rhinelander WI
I agree that the breaker did its job. It is a molded case breaker and I have never seen these tested. I didn't mention in my original post that the fault was spectacular. Well burned 3/0 conductors. All the magic smoke let out!! I reset a few 100A + breakers in my time in the paper industry and they seemed to be just fine. Another electrical contractor will have to foot the bill for this breaker (3K$). It was a goof on thier part but I have a certain amount sympathy for these guys. (Thier goofs recently have lead to a lot of buisiness for me lately!!):)
 
ericsherman37

ericsherman37

Senior Member
Location
Oregon Coast
Yeah I don't know what the recommendations are on replacing breakers after they clear a phase-to-phase fault (or two, for that matter). I imagine the manufacturer would encourage us to buy a new one every time one trips, right? :roll:
 
M

massfd

Member
If we are going to replace breakers after they clear a fault why did we ever get away from using fuses??
 
brian john

brian john

Senior Member
Location
Leesburg, VA
massfd said:
If we are going to replace breakers after they clear a fault why did we ever get away from using fuses??
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Because if this is a fault that operates at the top of the instantaneous rating (assuming adjustable instantaneous ) and the available fault current is at the limit for the CB IMO, the CB must be meggered and DLRO/Ductored/micro-ohmed.

Last week I failed 2 CB's after a close to a bolted fault condition, opened under a core drill accident.

I have the exact NEMA specs and will post them when I get in the office, there are visual signs that are included when replacement should be considered.

Circuit breakers are not necessarily reusable devices.
 
brian john

brian john

Senior Member
Location
Leesburg, VA
Two men ended up in the hospital one seriously injured when closing this CB after a fault. The feeder had shorted down stream, they fixed the problem and closed this CB.

CircuitBreakers.jpg


The intent should be all electricians should go home in the same shape they came to work in.
 
J

jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
PE (Retired) - Power Systems
Molded case breakers are tested to clear a fully rated (AIC) fault once. Well actually the test procedure is to close the breaker onto a maximum fault, open and clear the fault, and then be able to be closed again.

Calculate how much current was cleared by the breaker. But based on the conductor damage, I vote for simply replacing the breaker.
 
M

massfd

Member
That breaker looks like it was closed into a fault, why would it arc like that closing into an open or lightly loaded circuit
 
iaov

iaov

Senior Member
Location
Rhinelander WI
brian john said:
Two men ended up in the hospital one seriously injured when closing this CB after a fault. The feeder had shorted down stream, they fixed the problem and closed this CB.

CircuitBreakers.jpg


The intent should be all electricians should go home in the same shape they came to work in.
Click to expand...
Thanks for the pic . I'm going to play it safe and replace the breaker as the guy thats paying for it is not objecting. A few years back a guy I worked wiyh closed a 1200A breaker for a 2300 vt motor without knowing that the starter contacts were welded in. The results were spectacular!! Fortunatley he was standing off to the side with his back to the breaker when it blew. It singed the hair on one side of his head and I believe he required a change of under wear!:grin:
 
brian john

brian john

Senior Member
Location
Leesburg, VA
massfd said:
That breaker looks like it was closed into a fault, why would it arc like that closing into an open or lightly loaded circuit
Click to expand...

The damage was done (we surmise) from the first fault, carbon and metal fragments compromised the insulation integrity and upon closing the second time after the repair the CB faulted internally.
 
S

sparky 134

Senior Member
Location
Joliet, IL
A journeyman taught me a long time ago to stand to the side when closing a disconnect or c/b. Since copper turns molten around 35K F (I believe) I prefer to be out of the line of fire.
 
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