Alternate investment methods: Calculate Numbers of Pipe Earthing

Earthing is very important aspect for both Domestic and industrial applications. But there is always need to know how many earthings are required for connecting the system , below and above that mark could not serve the required purpose.

Below is given the formula for calculating no. of earthings required for the system.

The Earth Resistance of Single Rod or Pipe electrode is calculated as per BS 7430:
R=ρ/2×3.14xL (loge (8xL/d)-1)
Where ρ=Resistivity of Soil (Ω Meter),
L=Length of Electrode (Meter),
D=Diameter of Electrode (Meter)
Example:
Calculate Isolated Earthing Rod Resistance. The Earthing Rod is 4 Meter Long and having 12.2mm Diameter, Soil Resistivity 500 Ω Meter.
R=500/ (2×3.14×4) x (Loge (8×4/0.0125)-1) =156.19 Ω.
The Earth Resistance of Single Rod or Pipe electrode is calculated as per IS 3040:
R=100xρ/2×3.14xL (loge(4xL/d))
Where ρ=Resistivity of Soil (Ω Meter),
L=Length of Electrode (cm),
D=Diameter of Electrode (cm)
Example:
Calculate Number of CI Earthing Pipe of 100mm diameter, 3 Meter length. System has Fault current 50KA for 1 Sec and Soil Resistivity is 72.44 Ω-Meters.

Current Density At The Surface of Earth Electrode (As per IS 3043):
Max. Allowable Current Density I = 7.57×1000/(√ρxt) A/m2
Max. Allowable Current Density = 7.57×1000/(√72.44X1)=889.419 A/m2
Surface area of one 100mm dia. 3 meter Pipe= 2 x 3.14 x r x L=2 x 3.14 x 0.05 x3 = 0.942 m2
Max. current dissipated by one Earthing Pipe = Current Density x Surface area of electrode
Max. current dissipated by one Earthing Pipe = 889.419x 0.942 = 837.83 A say 838 Amps
Number of Earthing Pipe required =Fault Current / Max.current dissipated by one Earthing Pipe.
Number of Earthing Pipe required= 50000/838 =59.66 Say 60 No’s.
Total Number of Earthing Pipe required = 60 No’s.
Resistance of Earthing Pipe (Isolated) R=100xρ/2×3.14xLx(loge (4XL/d))
Resistance of Earthing Pipe (Isolated) R=100×72.44/2×3.14x300x(loge (4X300/10))=7.99 Ω/Pipe
Overall resistance of 60 No of Earthing Pipe=7.99/60=0.133 Ω.