The Earth electrodes should be designed to withstand the fault current without any physical damages. The fault current carrying capacity of a material mainly depends on cross sectional area of that particular material. In this article, we shall discuss about the current carrying capacity of pipes and strips of different dimensions and different materials as specified by IS 3043:2018.
In general, the amount of electric current flowing per unit cross sectional area of a material is called current density of a material. The current density of the earth electrode can also be calculated by the formula specified in IS 3043,
S = Cross sectional area, in mm²
I = value of fault current, in Amps
t = operating time of disconnecting device, in sec
k = factor dependent on the material of the protective conductor, the insulation and other
parts, and the initial and final temperatures.
For the specific cross sectional area, the current density can be calculated from the above
formula. These values are applicable only for disconnection times not exceeding 5 sec.
Cross sectional area of pipe,
R -> Outer diameter of the pipe = D/2 r -> Inner diameter of the pipe = (D – 2T)/ 2 (Where T is the thickness of pipe)
Current carrying capacity of Class A, B and C Steel for t = 1s:
Initial temperature: 40 ͦC, Final temperature: 500 ͦ C
R.M.S current density k for steel at given temperature= 80 A/ mm²
Note: These values are specified in IS 3043.
Current carrying capacity of Copper pipe for t = 1s:
Initial temperature: 40 ͦC, Final temperature: 395 ͦC R.M.S current density k for copper at given temperature= 205 A/ mm²
Fault current carrying capacity of Copper & Steel strip for t = 1s:
From the above calculations based on IS3043:2018, we can conclude that the fault current
carrying capacity mainly depends on cross-sectional area and the material of the electrode.
From the above calculations, we can find that
1) Current carrying capacity of 48mm dia. pipe is not same for all the classes and it depends on the class of the pipe.
2) Current carrying capacity of strips of different materials (Copper and Steel) having same cross sectional area (300Sq.mm) won’t be same.