Earthing Conductor size Calculation Formula & calculator

Earthing conductor size calculator:

Earthing conductor is used to carrying the electrical fault current to the ground. Here our earthing size calculator is used to calculate the exact required earthing conductor size in sqmm.

Enter the fault current in kilo Amps and fault clearing time in Sec. Then press the calculate button to get the required earth conductor size in Sqmm.

Choose Material:
Enter Fault Current in kilo Amps: kA
Enter Fault Clearing Times: Sec
Result Earth Conductor size: Sqmm

Earthing conductor size calculation Formula:

Earth conductor size PE(Sqmm) in sqmm is equal to the square root of maximum operating time t(S) in Seconds times of fault current square I(fault-A) divided by material constant k. Hence we can write the formula for finding earth conductor size as below,

 Earth conductor size PE(Sqmm) =  (I(Fault-A)2 x t(s)) / k

Material Material Constant (k)
GI 80
Copper 205
Aluminium 126
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But by considering Safety factor as 1.5,

Earth conductor size PE(Sqmm) =1.5 x  (I(Fault-A)2 x t(s)) / k

Here safety factor is your choice,


Let we calculate the required GI earth conductor size for 20kA Fault Current at 0.5 sec.

Use our formula,

Earth Conductor size = (200002 x 0.5) / 80

= 20000 x 0.707 / 80

= 176.8 Sqmm

Approximately 185Sqmm.

Generally, GI is availed in the busbar structure hence Or You can take any combination of conductor size such as 50×3.5 Sqmm or 25x8Sqmm etc.

However, the size of the conductor is above the resultant size.

Video Explanation for earth conductor size calculation


  1. according to your calculator the earthing conductor size for 50 KA Fault is about 250 mm2
    but when using Etap with the same values it give 150 mm2

  2. please tell me how to find fault current in case of industrial solar system,

    in some cases there is no transformer so how to find fault current.


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