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  1. #1
    Richard Stanley's Avatar
    Richard Stanley Guest

    Default How hot is too hot?

    This is in reference to some info posted on another bb regarding the temperature differential of circuit breakers in panels. The info stated that the NFPA 70B indicated that a temp diff of 27f required service/attention/repair etc. The subject of the thread was relevant to thermal imaging. I have never been able to get a definitive answer as to how hot is too hot. The poster did not have the specific text. He said he got the info from a camera manufacturer. '70B is for maintenance. I do not have the specific section. Does any one have that publication? If so, could you post the referenced material or the reference?

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  2. #2
    Join Date
    Mar 2007
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    Default Re: How hot is too hot?

    I don't have 70B, but I found this ( Electric Analysis ) and it contains this (bold is mine): "NOTE: The above criteria is subjective and has been determined by past field experience for maintenance scheduling."

    Jerry Peck, Construction / Litigation Consultant
    Construction Litigation Consultants, LLC ( www.ConstructionLitigationConsultants.com )
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  3. #3
    Richard Stanley's Avatar
    Richard Stanley Guest

    Default Re: How hot is too hot?

    Thanks Jerry.
    This is the text from the other bb. (Its the new infrared bb by Kevin Richardson)
    Infrared Thermal Imaging (ITI) Message Board - Index
    "The most common Delta-T criteria used by thermographers is NFPA-70B. This Standard sets forth the guidelines for both Delta-T and recommended actions based on those Delta-Ts. With a Delta-T of 7.3 deg to 14.4 deg, it's considered to be in the Alert category and action is suggested to be taken during the next scheduled maintenance. The next level, 14.5 deg to 27.0 deg falls in the Severe category. This is considered the second stage and should be repaired before the next scheduled maintenance and in a timely manner. The final stage, which is considered Critical, is a connection that has a Delta-T greater than 27.0 deg. This is considered the Acute Stage and should be repaired immediately."

    Still another post refers to UL criteria and max of 54F.

    I'm beginning to think that what I thought was a smart-ass answer by an electrician in an IR class was best - "if it is melted or burned - it is too hot."

    Last edited by Richard Stanley; 12-21-2007 at 06:01 AM. Reason: add info

  4. #4
    Peter Plein's Avatar
    Peter Plein Guest

    Default Re: How hot is too hot?

    This is a question always asked by newbie thermographic inspectors, usually the non electrician type. I believe most of the standard quoted refer to the temperature of an electrical connection not the face of the breaker ( the original question ). Many inexperienced themographers post great looking IR photos of "hot" breakers as examples of the kind of problems their "high tech equipment" can find. In most cases defective breakers present heat signatures down on the line side of the case not the face. I have seen Square D QO breakers with a 35f degree rise when loaded to 70-80 %. Voltage drop measuments prove there is nothing wrong. Trying to do electrical inspections with only a go-nogo list of parameters and limited electrical knowlege spells trouble, especially in the commercial world.


  5. #5
    Peter Plein's Avatar
    Peter Plein Guest

    Default Re: How hot is too hot?

    Just some examples. One is a problem the other is not

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