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Thread: Main Breaker failure?

  1. #21
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    From earlier description of OP, it seemed like he had a 4 pole breaker.

    Quote Originally Posted by Robrilo View Post
    ~All (4) terminals of the main breaker appeared to be in good visual condition showing no sign of loose connection nor heating.
    Quote Originally Posted by kwired View Post
    Some might look like a 4 pole unit, but are listed as a 2 pole unit.
    They are not connected to the neutral conductor either.
    If breaker did not operate due to any current in the neutral, then perhaps an arc flash event inside the breaker might have caused the explosion.

  2. #22
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    Quote Originally Posted by Sahib View Post
    From earlier description of OP, it seemed like he had a 4 pole breaker.





    If breaker did not operate due to any current in the neutral, then perhaps an arc flash event inside the breaker might have caused the explosion.
    All 4 terminals of the breaker would be two line side terminals and two load side terminals.

    I still find it hard to believe a high voltage surge would destroy the main breaker and nothing else.

    I think there is greater chance something went wrong in that breaker that resulted in excessive heating - very likely took some time to occur, as in months or years even. It eventually turned into "glowing connection" which is where most of the mess left behind came from. It finally resulted in line to line fault and that ultimately took out the transformer.

    Even if local distribution is only 2.4 kV - see a lot of that in small communities here, it still causes damages elsewhere in the house whenever I have followed up on an incidental contact sending 2.4 kV to the house.

    If it were 34.5 kV, or higher that made incidental contact - I have seen results of that as well - it causes damage in more then just one house - every time, will even jump over to shield on communications cables and find damages on other facilities that came through the phone lines.

  3. #23
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    Quote Originally Posted by kwired View Post
    All 4 terminals of the breaker would be two line side terminals and two load side terminals.

    I still find it hard to believe a high voltage surge would destroy the main breaker and nothing else.

    I think there is greater chance something went wrong in that breaker that resulted in excessive heating - very likely took some time to occur, as in months or years even. It eventually turned into "glowing connection" which is where most of the mess left behind came from. It finally resulted in line to line fault and that ultimately took out the transformer.

    Even if local distribution is only 2.4 kV - see a lot of that in small communities here, it still causes damages elsewhere in the house whenever I have followed up on an incidental contact sending 2.4 kV to the house.

    If it were 34.5 kV, or higher that made incidental contact - I have seen results of that as well - it causes damage in more then just one house - every time, will even jump over to shield on communications cables and find damages on other facilities that came through the phone lines.
    Considering the 50kva pole pigs here are fed from 19,920V fused at 50-75A, I dont think even a bolted fault on the secondary would wipe the xfmr before wires/breakers burned in two. 19,920/240 x 75 = 6225A secondary side, doubt a fault at a residential service could even pop the primary fuse. ofc if the same xfmr was fed from 2400v, I could see the fuse going - op never responded back if it was the xfmr or primary fuse being replaced... i dont see the POCO getting a service truck to a neighborhood, identifying the xfmr is bad, and replacing said xfmr in 3 hours in the middle of the night.

    I do like your idea of the fault originating at the breaker caused it to burn but afaik all newer ones have a minimum 10kAIC rating and shouldnt blow apart with any fault current less than 10kA.

    Anyone who can calculate maximum fault current available at a panel fed from a 50kva pole-mount xfmr with say 200' of 4/0 AL between the two?

    eta: just realized that the original post doesnt really say if the breaker burned up or blew apart, but i wouldnt expect either to lunch a transformer
    Electricians do it until it Hertz!

  4. #24
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    "Electricity is really just organized lightning." George Carlin


    Derek

  5. #25
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    Quote Originally Posted by JFletcher View Post
    Considering the 50kva pole pigs here are fed from 19,920V fused at 50-75A, I dont think even a bolted fault on the secondary would wipe the xfmr before wires/breakers burned in two. 19,920/240 x 75 = 6225A secondary side, doubt a fault at a residential service could even pop the primary fuse. ofc if the same xfmr was fed from 2400v, I could see the fuse going - op never responded back if it was the xfmr or primary fuse being replaced... i dont see the POCO getting a service truck to a neighborhood, identifying the xfmr is bad, and replacing said xfmr in 3 hours in the middle of the night.

    I do like your idea of the fault originating at the breaker caused it to burn but afaik all newer ones have a minimum 10kAIC rating and shouldnt blow apart with any fault current less than 10kA.

    Anyone who can calculate maximum fault current available at a panel fed from a 50kva pole-mount xfmr with say 200' of 4/0 AL between the two?

    eta: just realized that the original post doesnt really say if the breaker burned up or blew apart, but i wouldnt expect either to lunch a transformer
    Probably went like this.....customer calls about loud bag and no power, on call crew replaces blown primary fuse, which immediately blows again (maybe with some fireworks). Crew grabs another transformer from the yard and replaces the questionable one. New fuse holds, all is well except customer still has no power. Electrician is called during all of this.... I can see that taking under three hours.

    Maybe not, but it makes for a good story.

  6. #26
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    Quote Originally Posted by JFletcher View Post

    I do like your idea of the fault originating at the breaker caused it to burn but afaik all newer ones have a minimum 10kAIC rating and shouldnt blow apart with any fault current less than 10kA.

    Anyone who can calculate maximum fault current available at a panel fed from a 50kva pole-mount xfmr with say 200' of 4/0 AL between the two?

    eta: just realized that the original post doesnt really say if the breaker burned up or blew apart, but i wouldnt expect either to lunch a transformer
    My theoretical story of what might of happened wasn't a sudden fault on an otherwise good condition breaker blowing it up, it was a breaker that possibly has some age, developed a resistance on some internal component which heated things up and continued to deteriorate things. By the time any sort of high current fault developed things were weakened. "Shouldn't blow up" on a 10 kA fault only applies to something in good condition.

    Quote Originally Posted by meternerd View Post
    Probably went like this.....customer calls about loud bag and no power, on call crew replaces blown primary fuse, which immediately blows again (maybe with some fireworks). Crew grabs another transformer from the yard and replaces the questionable one. New fuse holds, all is well except customer still has no power. Electrician is called during all of this.... I can see that taking under three hours.

    Maybe not, but it makes for a good story.
    How fast this might get fixed also depends some on how big of a system the POCO operates, how far from the shop the problem area is, and how many lineman respond to the call. Might just be one guy show up initially in some cases, until they find out what the problem is. Certain tasks may require at least one additional trained person be present before they can be performed.

  7. #27
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    I can't believe a residence would present enough of a load to cause even a compromised breaker to fail in that way. Breakers don't blow up with probably 20 amps on them. It's also beyond the realm of possibility that this had nothing to do with the POCO event.

    I believe that this was a high voltage event even though you say that you haven't found anything damaged. Yet.


    -Hal

  8. #28
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    Quote Originally Posted by hbiss View Post
    I can't believe a residence would present enough of a load to cause even a compromised breaker to fail in that way. Breakers don't blow up with probably 20 amps on them. It's also beyond the realm of possibility that this had nothing to do with the POCO event.

    I believe that this was a high voltage event even though you say that you haven't found anything damaged. Yet.


    -Hal
    The scenario I was trying to describe doesn't need a high load. We more commonly see poor connection on a lug do what I was describing but if resistance develops within the breaker you can get the same thing - "glowing connection" doesn't need all that much current to happen. If it happens within breaker it is going to melt/burn plastic which may allow components secured by that plastic to move, all sorts of possible things can happen once this starts.


    Say you developed only .10 ohms resistance in a component, more likely in a joint between two components, and assume a current of 30 amps. Current will be higher at times and lower at times but just assume 30 for now. 30 amps across a .10 ohm resistance will give you 3 volts drop across that poor connection. 3 volts x 30 amps is 90 watts of heat that will be given up by that poor connection - that is a lot of heat if concentrated on a small area- soldering pencils can be only 15-25 watts

  9. #29
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    From the OP: Client reports a loud noise awoke them... components from the breaker strewn along the bottom of the cabinet.
    I agree with what you are saying but it just seems to be more than that. I know that a lot of this is anecdotal but the OP felt that the breaker exploded. What we didn't hear about is what the repair was (I assume at least a panel replacement) or see any pictures.

    -Hal

  10. #30
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    Quote Originally Posted by hbiss View Post
    I agree with what you are saying but it just seems to be more than that. I know that a lot of this is anecdotal but the OP felt that the breaker exploded. What we didn't hear about is what the repair was (I assume at least a panel replacement) or see any pictures.

    -Hal
    And it still might have exploded, after being weakened by other conditions and finally a fault developed that finished it off.

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