Calculate Earthing Strip Size for Electrical Equipment’s in Power Distribution Network
December 30, 2024 5 Comments
EXAMPLE:
Calculate Earthing Strip / Cable Size for Electrical Equipment’s / Panels in Power Distribution Networks.
- At RMU
- At Transformer
- At D.G Set
- At Main Distribution Panel
- At Sub Panel-1
- At Sub Panel-2
CALCULATION:
(1) Earthing Strip Size at RMU:
- Shot circuit capacity at RMU is 18.37 KA for 1 Second.
- Corrosion in Strip is 1% per year
- Earthing Strip shall be replaced after 25 Years.
- Safety Factor for Strip is 1.5
- Earthing Strip Material is GI
Calculation
- As per IS: 3043, clause 17.2.2.1:
- Cross section area of Earthing Strip (A) =(Isc x√t)/k
- Where Isc= Shot circuit current capacity in Ampere.
- t= Time for Shot circuit current in Second.
- K= Material Constant
| Bare Conductor Material with No Risk of Fire or Danger to any Other Touching or Surrounding Material | ||
| TABLE 11A (IS:3043) | ||
| Material | K value (1 second) | K value (2 second) |
| Steel | 80 | 46 |
| Aluminum | 126 | 73 |
| Copper | 205 | 118 |
- Cross section area of Earthing Strip (A) = (Isc x√t)/k
- Cross section area of Earthing Strip (A) = (18.37×1000 x√1)/80
- Cross section area of Earthing Strip (A) = 229.69 Sq.mm
- Allowable corrosion =1% per Year
- No of Year for replacement = 25 Year
- Allowable corrosion in 25 Years = 229.69x1x25% =57.40 Sq.mm
- Allowable Safety Factor = 229.69×1.5%=3.44 Sq.mm
- Required Earthing Strip size = Cross sectional area + Total Corrosion allowance + Safety factor
- Required Earthing Strip size=229.69+57.40+3.44 Sq.mm
- Required Earthing Strip size=290.47 Sq.mm
- Proposed GI Earthing Strip shall be 50×6 mm = 300 Sq.mm.
- Here Proposed Earthing Strip Size > Required Earthing Strip Size
- Proposed Earthing Strip is OK
(2) Earthing Strip Size at Transformer:
- Shot circuit capacity at Transformer is 25.32 KA for 1 Second.
- Corrosion in Strip is 1% per year
- Earthing Strip shall be replaced after 25 Years.
- Safety Factor for Strip is 1.5
- Earthing Strip Material for Transformer Neutral is Copper
- Earthing Strip Material for Transformer Body is GI
Calculation
- For Neutral
- As per IS: 3043, clause 17.2.2.1:
- Cross section area of Earthing Strip (A) =(Isc x√t)/k
- Where Isc= Shot circuit current capacity in Ampere.
- t= Time for Shot circuit current in Second.
- K= Material Constant
| Bare Conductor Material with No Risk of Fire or Danger to any Other Touching or Surrounding Material | ||
| TABLE 11A (IS:3043) | ||
| Material | K value (1 second) | K value (2 second) |
| Steel | 80 | 46 |
| Aluminum | 126 | 73 |
| Copper | 205 | 118 |
- Cross section area of Earthing Strip (A) = (Isc x√t)/k
- Cross section area of Earthing Strip (A) = (25.32×1000 x√1)/205
- Cross section area of Earthing Strip (A) = 125.51 Sq.mm
- Allowable corrosion =1% per Year
- No of Year for replacement = 25 Year
- Allowable corrosion in 25 Years = 125.51 x1x25% =30.87 Sq.mm
- Allowable Safety Factor = 125.51 x1.5%=1.85 Sq.mm
- Required Earthing Strip size = Cross sectional area + Total Corrosion allowance + Safety factor
- Required Earthing Strip size=125.51+30.87+1.85 Sq.mm
- Required Earthing Strip size=156.24 Sq.mm
- Proposed Cu Earthing Strip shall be 32×6 mm = 192 Sq.mm.
- Here Proposed Earthing Strip Size > Required Earthing Strip Size
- Proposed Earthing Strip is OK
- For Body
- As per IS: 3043, clause 17.2.2.1:
- Cross section area of Earthing Strip (A) =(Isc x√t)/k
- Where Isc= Shot circuit current capacity in Ampere.
- t= Time for Shot circuit current in Second.
- K= Material Constant
| Bare Conductor Material with No Risk of Fire or Danger to any Other Touching or Surrounding Material | ||
| TABLE 11A (IS:3043) | ||
| Material | K value (1 second) | K value (2 second) |
| Steel | 80 | 46 |
| Aluminum | 126 | 73 |
| Copper | 205 | 118 |
- Cross section area of Earthing Strip (A) = (Isc x√t)/k
- Cross section area of Earthing Strip (A) = (25.32 x1000 x√1)/80
- Cross section area of Earthing Strip (A) = 316.5 Sq.mm
- Allowable corrosion =1% per Year
- No of Year for replacement = 25 Year
- Allowable corrosion in 25 Years = 316.5 x1x25% =79.12 Sq.mm
- Allowable Safety Factor = 316.5 x1.5%=4.74 Sq.mm
- Required Earthing Strip size = Cross sectional area + Total Corrosion allowance + Safety factor
- Required Earthing Strip size=316.5+79.12+4.74 Sq.mm
- Required Earthing Strip size=400.37 Sq.mm
- Proposed GI Earthing Strip shall be 75×6 mm = 450 Sq.mm.
- Here Proposed Earthing Strip Size > Required Earthing Strip Size
- Proposed Earthing Strip is OK
(3) Earthing Cable Size at D.G Set:
- Shot circuit capacity at D.G Set is 10KA for 1 Second.
- Corrosion in Strip is 1% per year
- Earthing Strip shall be replaced after 25 Years.
- Safety Factor for Strip is 1.5
- Earthing Wire Material is Copper, XLPE Insulated
Calculation
- As per IS: 3043, clause 17.2.2.1:
- Cross section area of Earthing Strip (A) =(Isc x√t)/k
- Where Isc= Shot circuit current capacity in Ampere.
- t= Time for Shot circuit current in Second.
- K= Material Constant
| Insulated Protective Conductors Not Incorporated in Cables or Bare Conductors Touching Other Insulated Cables | ||
| TABLE 11B (IS:3043) | ||
| Material | K value (1 second) | K value (3 second) |
| Copper , PVC Insulated | 136 | 79 |
| Copper, Rubber Insulated | 150 | 92 |
| Copper, XLPE Insulated | 170 | 98 |
| Aluminum, PVC Insulated | 90 | 52 |
| Aluminum, Rubber Insulated | 106 | 61 |
| Aluminum, XLPE Insulated | 112 | 65 |
| Steel, PVC Insulated | 49 | 28 |
| Steel, Rubber Insulated | 58 | 33 |
| Steel, XLPE Insulated | 62 | 36 |
- Cross section area of Earthing Strip (A) = (Isc x√t)/k
- Cross section area of Earthing Strip (A) = (10×1000 x√1)/170
- Cross section area of Earthing Strip (A) = 58.82 Sq.mm
- Allowable corrosion =1% per Year
- No of Year for replacement = 25 Year
- Allowable corrosion in 25 Years = 58.82x1x25% =14.70 Sq.mm
- Allowable Safety Factor = 58.82 x1.5%=0.88 Sq.mm
- Required Earthing Strip size = Cross sectional area + Total Corrosion allowance + Safety factor
- Required Earthing Strip size=58.82+14.7+0.88 Sq.mm
- Required Earthing Strip size=74.41 Sq.mm
- Proposed Earthing Single Core Copper, XLPE Cable=95 Sq.mm
- Here Proposed Earthing Cable Size > Required Earthing Cable Size
- Proposed Earthing Cable is OK
(4) Earthing Strip Size at Main Panel :
- Shot circuit capacity at Main Panel is 21 KA for 1 Second.
- Corrosion in Strip is 1% per year
- Earthing Strip shall be replaced after 25 Years.
- Safety Factor for Strip is 1.5
- Earthing Strip Material is GI
Calculation
- As per IS: 3043, clause 17.2.2.1:
- Cross section area of Earthing Strip (A) =(Isc x√t)/k
- Where Isc= Shot circuit current capacity in Ampere.
- t= Time for Shot circuit current in Second.
- K= Material Constant
| Bare Conductor Material with No Risk of Fire or Danger to any Other Touching or Surrounding Material | ||
| TABLE 11A (IS:3043) | ||
| Material | K value (1 second) | K value (2 second) |
| Steel | 80 | 46 |
| Aluminum | 126 | 73 |
| Copper | 205 | 118 |
- Cross section area of Earthing Strip (A) = (Isc x√t)/k
- Cross section area of Earthing Strip (A) = (21 x1000 x√1)/80
- Cross section area of Earthing Strip (A) = 262.5 Sq.mm
- Allowable corrosion =1% per Year
- No of Year for replacement = 25 Year
- Allowable corrosion in 25 Years = 262.5 x1x25% =65.62 Sq.mm
- Allowable Safety Factor = 262.5 x1.5%=3.93 Sq.mm
- Required Earthing Strip size = Cross sectional area + Total Corrosion allowance + Safety factor
- Required Earthing Strip size=262.5+65.62+3.93 Sq.mm
- Required Earthing Strip size=332.06 Sq.mm
- Proposed GI Earthing Strip shall be 75×6 mm = 450 Sq.mm.
- Here Proposed Earthing Strip Size > Required Earthing Strip Size
- Proposed Earthing Strip is OK
(5) Earthing Strip Size at Sub Panel-1 :
- Shot circuit capacity at Sub Panel-1 is 11 KA for 1 Second.
- Corrosion in Strip is 1% per year
- Earthing Strip shall be replaced after 25 Years.
- Safety Factor for Strip is 1.5
- Earthing Strip Material is GI
Calculation
- As per IS: 3043, clause 17.2.2.1:
- Cross section area of Earthing Strip (A) =(Isc x√t)/k
- Where Isc= Shot circuit current capacity in Ampere.
- t= Time for Shot circuit current in Second.
- K= Material Constant
| Bare Conductor Material with No Risk of Fire or Danger to any Other Touching or Surrounding Material | ||
| TABLE 11A (IS:3043) | ||
| Material | K value (1 second) | K value (2 second) |
| Steel | 80 | 46 |
| Aluminum | 126 | 73 |
| Copper | 205 | 118 |
- Cross section area of Earthing Strip (A) = (Isc x√t)/k
- Cross section area of Earthing Strip (A) = (11 x1000 x√1)/80
- Cross section area of Earthing Strip (A) = 137.5 Sq.mm
- Allowable corrosion =1% per Year
- No of Year for replacement = 25 Year
- Allowable corrosion in 25 Years = 137.5 x1x25% =34.37 Sq.mm
- Allowable Safety Factor = 137.5 x1.5%=2.06 Sq.mm
- Required Earthing Strip size = Cross sectional area + Total Corrosion allowance + Safety factor
- Required Earthing Strip size=137.5+34.37+2.06 Sq.mm
- Required Earthing Strip size=173.93 Sq.mm
- Proposed GI Earthing Strip shall be 32×6 mm = 192 Sq.mm.
- Here Proposed Earthing Strip Size > Required Earthing Strip Size
- Proposed Earthing Strip is OK
(5) Earthing Strip Size at Sub Panel-2 :
- Shot circuit capacity at Sub Panel-2 is 6 KA for 1 Second.
- Corrosion in Strip is 1% per year
- Earthing Strip shall be replaced after 25 Years.
- Safety Factor for Strip is 1.5
- Earthing Strip Material is GI
Calculation
- As per IS: 3043, clause 17.2.2.1:
- Cross section area of Earthing Strip (A) =(Isc x√t)/k
- Where Isc= Shot circuit current capacity in Ampere.
- t= Time for Shot circuit current in Second.
- K= Material Constant
| Bare Conductor Material with No Risk of Fire or Danger to any Other Touching or Surrounding Material | ||
| TABLE 11A (IS:3043) | ||
| Material | K value (1 second) | K value (2 second) |
| Steel | 80 | 46 |
| Aluminum | 126 | 73 |
| Copper | 205 | 118 |
- Cross section area of Earthing Strip (A) = (Isc x√t)/k
- Cross section area of Earthing Strip (A) = (6 x1000 x√1)/80
- Cross section area of Earthing Strip (A) = 75.0 Sq.mm
- Allowable corrosion =1% per Year
- No of Year for replacement = 25 Year
- Allowable corrosion in 25 Years = 75 x1x25% =18.75 Sq.mm
- Allowable Safety Factor = 75 x1.5%=1.12 Sq.mm
- Required Earthing Strip size = Cross sectional area + Total Corrosion allowance + Safety factor
- Required Earthing Strip size=75+18.75+1.12 Sq.mm
- Required Earthing Strip size=94.87 Sq.mm
- Proposed GI Earthing Strip shall be 25×6 mm = 150 Sq.mm.
- Here Proposed Earthing Strip Size > Required Earthing Strip Size
- Proposed Earthing Strip is OK
CONCLUSION:
- At RMU=GI Earthing Strip: 50x6MM
- At Transformer Neutral=CU Earthing Strip: 32x6MM
- At Transformer Body=GI Earthing Strip: 75x6MM
- At D.G Set=CU, XLPE Earthing Cable: 1Cx95 SQ.MM
- At Main Distribution Panel=GI Earthing Strip: 75x6MM
- At Sub Panel=1=GI Earthing Strip: 32x6MM
- At Sub Panel-2=GI Earthing Strip: 25x6MM.
JIGNESH PARMAR
thank you very mach MATE
my neighbour shifting transformer from front side of the building to backside of his building that is adjacent to my house pad mount oil transformer without safety clearence and not maintaining safe distance from my house.
Sir,
Do these calculations also stand for 33KV substation?
Dear sir,
Your shared knowlege is commendable and useful , but i want to know regarding the short circuit current calculation for 100KVA gas generator , becuase on its name plane Xd reactance /percentage impedance is not mentioned . please help
Thank you for your descriptive information Sir. I will be grateful if you could please send me details in a table format containing copper, Aluminium, and GI MS starting from 100kva to 1000kva for 11kv voltage class.
My name is Shashidhar C from Bangalore email transpowerteam@gmail.com