Calculate Numbers of Plate/Pipe/Strip Earthings (Part-3)

Calculate Min. Cross Section area of Earthing Conductor:

  • Cross Section Area of Earthing Conductor As per IS 3043
  • Cross Section Area of Earthing Conductor (A) =(If x√t) / K

  • Where t= Fault current Time (Second).
  • K= Material Constant.
  • Example:
  • Calculate Cross Section Area of GI Earthing Conductor for System has 50KA Fault Current for 1 second. Corrosion will be 1.0 % Per Year and No of Year for Replacement is 20 Years.
  • Cross Section Area of Earthing Conductor (A) =(If x√t) / K
  • Here If=50000 Amp
  • T= 1Second
  • K=80 (Material Constant, For GI=80, copper K=205, Aluminium K=126).
  • Cross Section Area of Earthing Conductor (A) =(50000×1)/80
  • Cross Section Area of GI Earthing Conductor (A)=625 Sq.mm
  • Allowance for Corrosion = 1.0 % Per Year & Number of Year before replacement say = 20 Years
  • Total allowance = 20 x 1.0% = 20%
  • Safety factor = 1.5
  • Required Earthing Conductor size = Cross sectional area x Total allowance x Safety factor
  • Required Earthing Conductor size = 1125 Sq.mm say 1200 Sq.mm
  • Hence, Considered 1Nox12x100 mm GI Strip or 2Nox6 x 100 mm GI Strips

 Thumb Rule for Calculate Number of Earthing Rod:

  • The approximate earth resistance of the Rod/Pipe electrodes can be calculated by
  • Earth Resistance of the Rod/Pipe electrodes R= K x ρ/L

  • Where ρ = Resistivity of earth in Ohm-Meter
  • L= Length of the electrode in Meter.
  • d= Diameter of the electrode in Meter.
  • K=0.75 if 25< L/d < 100.
  • K=1 if 100 < L/d < 600
  • K=1.2 o/L if 600 < L/d < 300
  • Number of Electrode if find out by Equation of R(d) =(1.5/N) x R

  • Where R(d) = Desired earth resistance
  • R= Resistance of single electrode
  • N= No. of electrodes installed in parallel at a distance of 3 to 4 Meter interval.
  • Example:
  • Calculate Earthing Pipe Resistance and Number of Electrode for  getting Earthing Resistance of 1 Ω ,Soil Resistivity of ρ=40, Length=2.5 Meter, Diameter of Pipe= 38 mm.
  • Here L/d = 2.5/0.038=65.78 so K=0.75
  • The Earth Resistance of the Pipe electrodes R= K x ρ/L =0.75×65.78=12 Ω
  • One electrode the earth resistance is 12 Ω.
  • To get Earth resistance of 1 Ω  the total Number of electrodes required =(1.5×12)/1 =18 No

 Calculating Resistance & Number of Earthing Rod:

  • Reference: As per EHV Transmission Line Reference Book page: 290 and Electrical Transmission & Distribution Reference Book Westinghouse Electric Corporation, Section-I Page: 570-590.
  • Earthing Resistance of Single Rods: R = ρx[ln (2L/a)-1]/(2×3.14xL)

  • Earthing Resistance of Parallel Rods: R = ρx[ln (2L/A]/ (2×3.14xL)

  • Where L= length of rod in ground Meter,
  • a= radius of rod Meter
  • ρ = ground resistivity, ohm- Meter
  • A= √(axS)
  • S= Rod separation Meter

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 Factor affects on Ground resistance:

  •  The NEC code requires a minimum ground electrode length of 2.5 meters (8.0 feet) to be in contact with the soil.  But, there are some factor that affect the ground resistance of a ground system:
  • Length / Depth of the ground electrode: double the length, reduce ground resistance by up to 40%.
  • Diameter of the ground electrode: double the diameter, lower ground resistance by only 10%.
  • Number of ground electrodes: for increased effectiveness, space additional electrodes at least equal to the depth of the ground electrodes.
  • Ground system design: single ground rod to ground plate.

 The GI Earthing Conductor sizes for various Equipments:      

No Equipments Earth Strip Size

1

HT switchgear, structures, cable trays & fence, rails, gate and steel column

55 X 6 mm (GI)

2

Lighting Arrestor

25 X 3 mm (Copper)

3

PLC Panel

25 X 3 mm (Copper)

4

DG & Transformer Neutral

50X6 mm (Copper)

5

Transformer Body

50X6 mm (GI)

6

Control & Relay Panel

25 X 6 mm (GI)

7

Lighting Panel & Local Panel

25 X 6 mm (GI)

8

Distribution Board

25 X 6 mm (GI)

9

Motor up to 5.5 kw

4 mm2 (GI)

10

Motor 5.5 kw to 55 kw

25 X 6 mm (GI)

11

Motor 22 kw to 55 kw

40 X 6 mm (GI)

12

Motor Above 55 kw

55 X 6 mm (GI)

 Selection of Earthing System:

Installations/       Isc Capacity

IR Value Required

Soil Type/ Resistivity

Earth System

House hold earthing/3kA 8 ohm Normal Soil/ up to 50 ohm-meter Single Electrode
Sandy Soil/ between 50 to 2000 ohm- meter Single Electrode
Rocky Soil/ More than 2000 ohm- meter Multiple Electrodes
Commercial premises,Office / 5kA 2 ohm Normal Soil/ up to 50 ohm-meter Single Electrode
Sandy Soil/ between 50 to 2000 ohm- meter Multiple Electrodes
Rocky Soil/ More than 2000 ohm- meter Multiple Electrodes
Transformers, substationearthing, LT line equipment/ 15kA less than 1 ohm Normal Soil/ up to 50 ohm-meter Single Electrode
Sandy Soil/ between 50 to 2000 ohm- meter Multiple Electrodes
Rocky Soil/ More than 2000 ohm- meter Multiple Electrodes
LA, High current Equipment./ 50kA less than 1 ohm Normal Soil/ up to 50 ohm-meter Single Electrode
Sandy Soil/ between 50 to 2000 ohm- meter Multiple Electrodes
Rocky Soil/ More than 2000 ohm- meter Multiple Electrodes
PRS, UTS, RTUs, Data processing centre etc./5KA less than 0.5 ohm Normal Soil/ up to 50 ohm-meter Single Electrode
Sandy Soil/ between 50 to 2000 ohm- meter Multiple Electrodes
Rocky Soil/ More than 2000 ohm- meter Multiple Electrodes

 Size of Earthing Conductor:

  • Ref IS 3043 &Handbook on BS 7671: The Lee Wiring Regulations by Trevor E. Marks.

Size of Earthing Conductor

Area of Phase Conductor S (mm2) Area of Earthing conductor (mm2) When It is Same Material as Phase Conductor Area of Earthing conductor (mm2) When It is Not Same Material as Phase Conductor
S < 16 mm2 S SX(k1/k2)
16 mm2<S< 35 mm2 16 mm2 16X(k1/k2)
S > 35 mm2 S/2 SX(k1/2k2)
K1 is value of Phase conductor,k2 is value of earthing conductor
Value of K for GI=80, Alu=126,Cu=205 for 1 Sec

 Standard Earthing Strip/Plate/Pipe/wire Weight:

GI Earthing Strip:

Size (mm2) Weight
20 x 3 500 gm Per meter
25 x 3 600 gm Per meter
25 x 6 1/200 Kg Per meter
32 x 6 1/600 Kg Per meter
40 x 6 2 Kg Per meter
50 x 6 2/400 Kg Per meter
65 x 10 5/200 Kg Per meter
75 x 12 7/200 Kg Per meter

 GI Earthing Plate:

Plate Weight
600 x 600 x 3 mm 10 Kg App.
600 x 600 x 4 mm 12 Kg App.
600 x 600 x 5 mm 15 Kg App.
600 x 600 x 6 mm 18 Kg App.
600 x 600 x 12 mm 36 Kg App.
1200 x 1200 x 6 mm 70 Kg App.
1200 x 1200 x 12 mm 140 Kg App.

 GI Earthing Pipe:

Pipe Weight
3 meter Long BISE 5 Kg App.
3 meter r Long BISE 9 Kg App.
4.5 meter (15′ Long BISE) 5 Kg App.
4.5 meter (15′ Long BISE) 9 Kg App.
4.5 meter (15′ Long BISE) 14 Kg App

 GI Earthing Wire:

Plate Weight
6 Swg 5 meter in 1 Kg
8 Swg 9 meter in 1 Kg
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About Jignesh.Parmar
Jignesh Parmar has completed M.Tech (Power System Control), B.E(Electrical) from Gujarat University. He has more than 14 years experience in Power Transmission-Power Distribution-Electrical energy theft detection-Electrical Maintenance-Electrical Projects(Planning-Designing-coordination-Execution). He is Presently associate with one of the leading business group as a Deputy Manager at Ahmedabad,India. He is Freelancer Programmer of Advance Excel and design useful Excel Sheets of Electrical Engineering as per IS,NEC,IEC,IEEE codes. He is technical Author for "Electrical Mirror" and "Electrical India" Magazines. He is Technical Blogger and Familiar with English, Hindi, Gujarati, French languages. He wants to Share his experience & knowledge and help technical enthusiasts to find suitable solutions and updating themselves on various Engineering Topics.

27 Responses to Calculate Numbers of Plate/Pipe/Strip Earthings (Part-3)

  1. Deepak Agrawal says:

    pls send something on capacitor power factor correction, by varying input voltage to capacitors, their KVAr can be changed, can we design such system, it could work as an APFC without switching ON/off of capacitors

  2. asadullah amiri says:

    Thank you very much from your help.

    Eng.Amiri

  3. narayan says:

    Thanks for sending electrical notes.

  4. Rahul says:

    Dear Sir,

    55 x 6 mm GI Strip is a standard size..?

    Regards

    Rahul

  5. sanjay says:

    Thanks for the information…..

  6. yogesh jadhav says:

    he is champ

  7. Mukesh aggarwal says:

    Send all electrical goods of industries rates with specifications
    Mukesh
    engineer electrical

  8. Vipin Gupta says:

    Great Information.

    keep it up.

  9. farhan says:

    mujey bi send kardey electrical i m student of electrical.mera last year chal raha hey agar notic to is id per send karday,.

  10. Noorudheen says:

    It was very useful information, from where I can get the K(materiel constant) value chart for GI Strips

  11. Rahul says:

    Dear Sir,

    Thank you for the valuable information.

    I have a query

    It seems like the equation for calculating the resistance of plate electrode and rod are different in IS 3043:1987 and BS 7430:1998

    Which is the right one..?

    Regards

    Rahul

  12. Vikas Singh says:

    First of all a zillion thanks for democratizing electrical knowledge for the world. I have shifted my career from electrical maintenance to designing and finding your articles very helpful. You have really upholded rig veda saying ‘Let knowledge come from every direction’
    Sir, regarding a project in Qatar I need the conductor size for COPPER for earthing non-current carrying metallic part like steel structures and process equipments like tanks, vessels, pipe rack, pipes, stairways, towers etc.
    If you can provide the data according to BS 7430 it will be best because I have to follow that standard in Qatar.

  13. Rajinder Prabhakar says:

    very use ful for estimating cost for quotating rates

  14. Karthick says:

    I am having two earth pits- Is it possible to combine the both earth pits and connect it for MCC Panel, 2*55 KW Motor, 0.37KW Motors. WIll it with stand

  15. ANANT D.LINGAYAT says:

    sir i required how to mtr to kg any gi and cu earthig size ,pls

  16. ravi says:

    sir,
    i want to know why cable or wires size are calculated in mm2.

  17. Prashant Lawand says:

    plz sir contact me my name is prashant lawand i am earthing electrode manufacturer in pune 9975977674

  18. harvinder Singh sethi says:

    Thanks Sir It is Very Much Informative.

  19. salah says:

    you mean Here If=50000 Amp is fault of system if you mean that what is relation between fault of system and earhtig?

  20. vamshi says:

    Number of Electrode if find out by Equation of R(d) =(1.5/N) x R
    how 65.78 value is taken in place of rho/l

  21. santosh says:

    how to do complete building electrification /house/commercial complex .plz send idea with real examples with estimatin and calculation

  22. Tp says:

    Sir
    Safety factor = 1.5
    But how ?

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