## 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.

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**Calculate Numbers of Pipe Earthing:**

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**Earthing Resistance & No of Rod for Isolated Earth Pit (Without Buried Earthing Strip):**

**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.**