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Thread: What happened here?

  1. #11
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    Quote Originally Posted by Jraef View Post
    but following the rule that heat rises
    My understanding is that hot air rises (convection), but heat transfer via conduction or radiation doesn't care about up or down. So is the upshot that in these forensic analyses, the heat flow via convection is usually a sufficiently large portion of the total heat flow that the damage will follow the rule "heat rises"?

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  2. #12
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    Quote Originally Posted by rhamblin View Post
    it would appear to be a loose connection on the B phase and as it loosened up it got warm. This runs a 40 HP pump. . The copper wire actually got so hot that it appears to have melted (separated just outside of the lug). The overload, I'm told never tripped and was never reset. Any thoughts are appreciated.
    The extreme heat at B phase terminal of CB might have changed its resistance and so current flow to the pump motor and so there might be voltage unbalance/single phasing to the pump motor. If the pump motor had any unbalance protection, it might have tripped.

  3. #13
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    Quote Originally Posted by Sahib View Post
    The extreme heat at B phase terminal of CB might have changed its resistance and so current flow to the pump motor and so there might be voltage unbalance/single phasing to the pump motor. If the pump motor had any unbalance protection, it might have tripped.
    That solid state OL relay has phase loss protection, but not phase current imbalance for levels above 20% of the setting (meaning it detects a phase loss when one phase is less than 20% of the set amount after the first 3 seconds). A slight imbalance increases the heat in the motor, but would not damage the OL relay terminal like that.
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  4. #14
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    Quote Originally Posted by wwhitney View Post
    My understanding is that hot air rises (convection), but heat transfer via conduction or radiation doesn't care about up or down. So is the upshot that in these forensic analyses, the heat flow via convection is usually a sufficiently large portion of the total heat flow that the damage will follow the rule "heat rises"?

    Cheers, Wayne
    I heard an interesting talk on the radio the other day by a forensic fire investigator about forest fires. He said that the burned area in a forest fire is usually roughly triangular in shape with the point of ignition at one of the triangle's vertices.

  5. #15
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    Quote Originally Posted by ggunn View Post
    I heard an interesting talk on the radio the other day by a forensic fire investigator about forest fires. He said that the burned area in a forest fire is usually roughly triangular in shape with the point of ignition at one of the triangle's vertices.
    I heard that too, very interesting. I immediately thought about wind, ANY wind, being the reason for the spread to be angular, but triangular? That implies that at some point, the progression of the fire proceeded in a straight line opposite the starting point.
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  6. #16
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    Quote Originally Posted by Jraef View Post
    I heard that too, very interesting. I immediately thought about wind, ANY wind, being the reason for the spread to be angular, but triangular? That implies that at some point, the progression of the fire proceeded in a straight line opposite the starting point.
    He said burn area... not burn path.
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  7. #17
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    And some would be perfectly happy to call a sector of a circle triangular.....

  8. #18
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    Quote Originally Posted by wwhitney View Post
    My understanding is that hot air rises (convection), but heat transfer via conduction or radiation doesn't care about up or down. So is the upshot that in these forensic analyses, the heat flow via convection is usually a sufficiently large portion of the total heat flow that the damage will follow the rule "heat rises"?

    Cheers, Wayne
    Actually, conduction also transfers heat [more] upward. Just nowhere near as much as it does with gaseous elements.
    I will have achieved my life's goal if I die with a smile on my face.

  9. #19
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    Quote Originally Posted by Smart $ View Post
    Actually, conduction also transfers heat [more] upward. Just nowhere near as much as it does with gaseous elements.
    Replace it with convection.
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  10. #20
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    Quote Originally Posted by Smart $ View Post
    Actually, conduction also transfers heat [more] upward. Just nowhere near as much as it does with gaseous elements.
    I do not see the physics or thermodynamics to support that.

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