insulation integrity

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johnnym

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Vermont
I was told recently by a master electrician that if a breaker trips do to a short circuit or ground fault, that the insulation integrity of the conductor supplying that circuit has been compromised and the conductor(s) should be replaced. Any thoughts? I believe the breaker (if it operates properly) should open the circuit before any conducter damage occors.


John
 

infinity

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New Jersey
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I agree with Bryan. If the OCPD is doing its job the insulation should be protected. Imagine having someone tell you to rewire a circuit every time the breaker tripped. Sounds rather foolish to me.
 

bphgravity

Senior Member
Location
Florida
I would think that small overloads (those that are small enough and not long enough to trip the breaker) would be more damaging to conductor insulation over the long run verses one or two short circuits or ground faults.

Perhaps a combination of both is even worse. Suppose you have #12 TW protected by a 20A breaker but is loaded to 35A periodically for several years. It is doubtful the overcurrent device would ever trip, perhaps stressing the insulation. Then you have a significant ground fault or short circuit event.

Perhaps then you might find some insulation damage. It is also likely some annealing of the terminations would show hot spots.
 

charlie b

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johnnym said:
I was told recently by a master electrician that if a breaker trips do to a short circuit or ground fault, that the insulation integrity of the conductor supplying that circuit has been compromised and the conductor(s) should be replaced. . . . I believe the breaker should open the circuit before any conducter damage occurs.
johnnym said:

You are right. The statement from the "master" sounds to me like a statement that a dishonest person might try to use on an unwary homeowner, in order to sell a repair job that does not need to be done.
 

don_resqcapt19

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Given that there is no UL requirement for a magnetic trip in a breaker there is the possiblity of conductor damage from a short circuit. I think that all of the common breakers do have magnetic trip, but the trip range is from 8 to 40 times the handle rating. The 40x trip can easily let enough current flow to exceed the I^2R damage curve of the conductor.
Don
 

bphgravity

Senior Member
Location
Florida
So Don, what does that mean?

Should we assume a worse case scenerio of 40X trip and design are circuits so as to not exceed I?R ratings? Is this what 110.10 is requiring?
 

charlie tuna

Senior Member
Location
Florida
you failed to mention -- this master electrician probibly had his life savings invested in the stock market----------- all in copper wire manufacturers!!!
 

ardy

Member
There are to many ways to test your conducters than to pull new in when your ocp opens. I've been in elect. maint. for almost 30yr. and have changed many fuses and reset many cicuit brks. and not had to pull new conducters.
 

johnnym

Member
Location
Vermont
Thanks for the input everyone. This is my first post and I didn't expect so many replies. It's good to know there's a place to go when you need help.

Did I mention that the master electrician I was referring to is my boss? He hates it when I prove him wrong.
 

zog

Senior Member
Location
Charlotte, NC
Well, replacing the conductors right off the bat is going overboard but he may be right about the conductor damage. A megger test will tell you if any damage has occured and in fact is required before re-energizing the circuit per OSHA 1910.342.
 

infinity

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zog said:
Well, replacing the conductors right off the bat is going overboard but he may be right about the conductor damage. A megger test will tell you if any damage has occured and in fact is required before re-energizing the circuit per OSHA 1910.342.


Could you post a link to OSHA 1910.342?
 

don_resqcapt19

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Illinois
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1910.334(b)(2) "Reclosing circuits after protective device operation." After a circuit is deenergized by a circuit protective device, the circuit protective device, the circuit may not be manually reenergized until it has been determined that the equipment and circuit can be safely energized. The repetitive manual reclosing of circuit breakers or reenergizing circuits through replaced fuses is prohibited.

Note: When it can be determined from the design of the circuit and the overcurrent devices involved that the automatic operation of a device was caused by an overload rather than a fault condition, no examination of the circuit or connected equipment is needed before the circuit is reenergized.
 

infinity

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don_resqcapt19 said:
1910.334(b)(2) "Reclosing circuits after protective device operation." After a circuit is deenergized by a circuit protective device, the circuit protective device, the circuit may not be manually reenergized until it has been determined that the equipment and circuit can be safely energized. The repetitive manual reclosing of circuit breakers or reenergizing circuits through replaced fuses is prohibited.

Note: When it can be determined from the design of the circuit and the overcurrent devices involved that the automatic operation of a device was caused by an overload rather than a fault condition, no examination of the circuit or connected equipment is needed before the circuit is reenergized.

Would you say that this requires you to megger a conductor as suggested by Zog?
 

bphgravity

Senior Member
Location
Florida
I just feel there are other reasonable methods that can be used as determined on a case-by-case basis. I do not feel a tripped breaker automatically concludes the circuit must have the insulation tested for integrity. Basic troubleshooting of the circuit and circuit components may reveal a problem or lead one to feel the circuit conductors should be tested further. Again however, not in all cases.

I worked at an agricultural facility for several years that had hundreds of motors. It was very evident when the motor failed resulting in an overload or ground-fault. It was also evident when the circuit conductors needed to be replaced. I just don't see any significant evidence of conductors failing rampantly around the national because the circuit was reenergized without an insulation test.

Is there anyone here that has NEVER reset a breaker before testing the circuit?
 

iwire

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Massachusetts
petersonra said:
I would ask if there is anyone here who has ever actually tested the circuit before reseting the breaker?

Darn few I imagine.

For me I will be honest, it depends on a lot of factors.

A 20 amp branch circuit supplying GP outlets?

Heck no, I am gonna go over and reset the breaker.

A 400 amp 480 volt feeder?

I will be doing some investigating before reseting but if I find an obvious fault not related to the conductors I will not be megging them.
 
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