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Thread: 2017 MAIN OCP Label

  1. #1
    Join Date
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    2017 MAIN OCP Label

    Curious on your take of 2017, 110.16 B 3 labelingrequirement.

    Are we simply stating bolted 3-P current value ? andcorresponding clearing time ?

    They are using term….”Available Fault Current” which is NOTdefined.

    Should we assume BOLTED, or Arcing fault values or BOTH ?
    Should we go even farther and list clearing times for BOTHin maintenance mode also ?

  2. #2
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    NFPA 70E 2018 Edition has a Definition of Fault Current, Available.

    Fault Current, Available. The largest amount of current capable
    of being delivered at a point on the system during a shortcircuit
    condition.
    There is a proposal to add this definition to the 2020 NEC. (I was part of the Task Group on this proposal)

    So to comply with the marking requirements of 2017 NEC 110.16(B)

    You would need to calculate the available fault current. One way to do this is use an available fault current calculator such as the Free APP by Eaton/Bussman.

    Chris

  3. #3
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    Pretty good article on this in the IAEI (inspectors association) magazine.

    https://iaeimagazine.org/magazine/20...-2017-110-16b/
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  4. #4
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    Thanks to you both....
    Article link spells out exactly what they are looking for.

  5. #5
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    Rutland, VT, USA
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    Quote Originally Posted by raider1 View Post
    NFPA 70E 2018 Edition has a Definition of Fault Current, Available.



    There is a proposal to add this definition to the 2020 NEC. (I was part of the Task Group on this proposal)

    So to comply with the marking requirements of 2017 NEC 110.16(B)

    You would need to calculate the available fault current. One way to do this is use an available fault current calculator such as the Free APP by Eaton/Bussman.

    Chris
    The only way to get the available fault current is from the utility. They will provide the available fault current at the point of connection to their system. If it is a padmount transformer, this would be at the fuse cutouts at the riser pole. For a pole mount cluster, this would be the fuses at the transformer primary. However, the code is requiring the available fault current at the service overcurrent device. The system will have to modeled from the utility point to the service overcurrent device to determine the fault current at that point. This will take into account the impedance of the transformer and conductors, both primary and secondary. So the transformer impedance is needed as well as the conductor impedance. Once the available fault current is calculated at the service overcurrent device then the time current curve for the overcurrent device is needed to determine the clearing time of the overcurrent device (also required on the label).

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