Calculate Numbers of Plate/Pipe/Strip Earthings (Part-3)
April 1, 2013 42 Comments
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
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 |
JIGNESH PARMAR
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
Thank you very much from your help.
Eng.Amiri
Thanks for sending electrical notes.
Dear Sir,
55 x 6 mm GI Strip is a standard size..?
Regards
Rahul
Thanks for the information…..
he is champ
Send all electrical goods of industries rates with specifications
Mukesh
engineer electrical
Yes Sir,
Give me your Address!!!!!!!
Dear sir please Send me all electrical goods of industries latest rates with specifications
sir will you please reply how did you calculate:cross sec area x safety factor x total allowance to 1125 sq.mm=625×1.5×20%=1125 say 1200 sir please reply….
Dear sir please Send me all electrical goods of industries latest rates with specifications.
Thanks for sharing all your amazing information.
I really appreciate it very much. It has been very useful.
Great Information.
keep it up.
i have also the same doubt
mujey bi send kardey electrical i m student of electrical.mera last year chal raha hey agar notic to is id per send karday,.
It was very useful information, from where I can get the K(materiel constant) value chart for GI Strips
Already given in the explanation…”K=80 (Material Constant, For GI=80, copper K=205, Aluminium K=126).” !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
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
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.
very use ful for estimating cost for quotating rates
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
sir i required how to mtr to kg any gi and cu earthig size ,pls
sir,
i want to know why cable or wires size are calculated in mm2.
plz sir contact me my name is prashant lawand i am earthing electrode manufacturer in pune 9975977674
Thanks Sir It is Very Much Informative.
you mean Here If=50000 Amp is fault of system if you mean that what is relation between fault of system and earhtig?
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
how to do complete building electrification /house/commercial complex .plz send idea with real examples with estimatin and calculation
Sir
Safety factor = 1.5
But how ?
Mr. Parmar,
Can you help me about earting.34,5/400 1000kVA power system. can you calculation earthing impedance in AG side.
Dear Sir,
I chose 3 mtr, 100 mm dia, 3.6 mm thickness pipe electrode for soil resistivity of 1360 ohm-mtr. but my calc. for earth rod required are not matching by thumb rule, acc. to formulas iI calc it as 259 electrodes but by thumb rule it is coming as 34. I am not getting why are you replacing rho/L with L/d? please help…
Dear Sir
thank you from your calculation
Sir can you share dc earting calculation also.
can u tell 25x3mm GI Flat equivalent Cu size?
How to calculate?
Very good information….we have to consider once system KA at equipment in question…fault ka should be calculated for line or phase to earth fault, am I right?
25x3mm GI Flat how can select for Lightning protection calculation
kindly give format /suggestion…
information is best for execution purpose. Thanks.
Sir, Can we use 25×3 MM GI flat for earthing of 11 KV system.
Dear Sir,
65 x 10 mm GI Strip is a standard size..?
PLEASE SEND STANDARD SIZE CHART
Regards
JAYESH
Thank You; Vast knowledge gained refering this page
Hi sir good morning
please share
us the how to calculated earth mat
Is there a way to calculate different earthing connected to each other.
Ex. we added hollow square earthing to equilateral triangle to parallels rods with plates.
How could I calculate the total resistance of this combination ?
is there any earthing calculations on the dc side for a solar generation
plant for the solar module mounting structure .