## Calculate Size of Motor-Pump Calculate Motor-Pump size:

• Calculate Pump Hydraulic Power
• Calculate Motor-Pump Shaft Power
• Calculate Pump Size.
• Calculate Motor Size.

## 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 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 ## 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 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