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Short circuit withstand of a panel

    • 129 posts
    July 23, 2019 2:15 PM PDT

    Hi everyone,

    I am just looking for a solution to determine the short circuit withstand of a panel.

    There are two points: 

    1. Three phase short circuit Ik"

    2. asymmetric peak short ciruit ip

     

    As per my point of view the short circuit withstand of a panel should be based on ip not Ik" since ip is a peak value. following is an example.

    I appreciate any explanation on this. 

     

     

    • 15 posts
    July 23, 2019 2:37 PM PDT

    The panel is rated by the mfg. The rating to determine should be the max short circuit calculation. The max short calculation should determine

    if the panel is rated properly. Which ever is greater, Ip or Ik , determines if the panel is adequate for the fault current.

    • 200 posts
    July 26, 2019 4:39 AM PDT
    Thanks for the suggestion of this topic, Hameed.

    Is this an urgent matter? If you can wait a bit longer, a reply has being prepared but it takes some time, currently it is 20% to 30% done. If you already rated the panel, it is not necessary to go further in this time consuming reply. Or we can discuss this in private, the partial reply can be sent.

    However, the use of Ip is not advised, a peak of a current for a very short time, to rate entire equipment. Ip, is a value to be used as a "Preventive" Flag on Protective Devices, it has a so short duration, less than a 50Hz or 60Hz cycle (or half cycle for that matter), that is "energetically" negligible, no other use than a preventive sign that a short circuit event could or will happen, a Protective Device setting only. The use of such value to rate entire equipment would increase the Cost excessively.

    If it is an urgent matter let's discuss this in private and then the conclusions we can post here later. Please, let me know.
    This post was edited by Alex de Moura at July 26, 2019 4:48 AM PDT
    • 129 posts
    July 26, 2019 11:32 AM PDT

    Thanks Alex I agree with you but the largest value of the short-circuit current is the peak short-circuit current. Ip has to be calculated to determine the making capacity of the required circuit breakers and to define the electrodynamic forces that the installation as a whole must be capable of withstanding. 


    This post was edited by Hameedullah Ekhlas at July 26, 2019 11:32 AM PDT
    • 17 posts
    July 26, 2019 1:51 PM PDT
    Try the Schneider publication:
    Cahier technique no. 158
    Calculation of short-circuit current
    If you can not find it in the Internet I can send you by email.
    • 17 posts
    July 26, 2019 1:51 PM PDT
    Try the Schneider publication:
    Cahier technique no. 158
    Calculation of short-circuit current
    If you can not find it in the Internet I can send you by email.
    • 200 posts
    July 26, 2019 3:18 PM PDT
    Juan thanks for your advice, SCHNEIDER Cahier 158, is the paper the 2nd image Hameed posted came from. As Hameed said "Ip has to be calculated to determine the making capacity of the required circuit breakers and to define the electrodynamic forces", however I disagree that Ip must be used to rate any equipment except a Protection device setting. It is a preventive setting only, it is too short to cause anything on any equipment. It is a preventive setting, it is a flag for Protective Devices trip preventively. It MUST be calculated for protection only but not to rate any other operational equipment.
    • 62 posts
    July 27, 2019 1:39 AM PDT

    I agree with Hameed. It should be considered but this is done by manufacturer company who build the switchboards.

    You need to provide the manufacturer company only 3 phase short circuit in each point, they will design the switchboards and they will also consider the electrodynamics forces.

    Attached is an example from Eaton

     

     

    • 22 posts
    July 28, 2019 5:16 PM PDT