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no image Monday, January 29, 2018 by Swati chouhan

Earthing cable calculation

What is the formula to calculate on size of Earthing cable used for Racks & power panels

Comments

  • by  P.N. Kaushika Hasith Jayantha (edited)

    In BS 7671 : 2008, under 543.1.3, following adiabatic equation has been provided for calculation of earth wire cross section area,


    S = sqrt (I*I*t)/k

    S = nominal cross sectional area of earth conductor in mm2

    I = value in amperes (rms for a.c.) of fault current for a fault of negligible impedance, which can flow through the associated protective device.

    t = is the operating time of the disconnecting device in seconds corresponding to the fault current I ampere

    k = this value depend on the cable construction and method of installation. Please use following links to select proper value.

    Table 1

    Table 2

    Table 3

    Table 4


    For further details, please refer Chapter 54 of BS 7678 and following link also may be helpful.

    Earthing

    Kaushika

  • by  P.N. Kaushika Hasith Jayantha (edited)

    In BS7678 : 2008, it has been given as adiabatic equation for calculation of cross sectional area of earth conductor as follows,

     

    S = sqrt(I*I*t)/k

     

    S = nominal cross section area of the earth conductor in mm2

    I = value in amperes (rms of a.c.) of fault current for a fault of negligible impedance, which can flow through the associated protective device.

    t = the opening time of disconnecting device in second corresponding to the fault current I amperes.

    K = this value is based on the construction of the conductor and usage of it. You can use following links to select suitable value.

    Table 1

    Table 2

    Table 3

    Table 4

    Table 5


     For further details please refer BS 7678 and following link also may be helpful.

    Earthing

    Kaushika

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