Formula for calculating earthing cable size for racks & power panels?

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

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)/kS = nominal cross sectional area of earth conductor in mm2I = 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 amperek = 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

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