Solar Plant Earthing Design Calculator

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Design a complete solar PV plant earthing system to IEEE Std 80: earth-grid conductor thermal sizing, grid geometry, earth-pit and rod quantity, Schwarz grid/rod/mutual resistance, grid current, GPR, tolerable and attainable touch, mesh and step voltage, plus transformer body, transformer neutral and equipment earthing.

Inputs

A — Project details

Project name

Plant capacity (MW AC)

DC capacity (MWp)

Plant type

System type

Evacuation / system voltage (kV)

System frequency (Hz)

Number of inverter stations

Number of transformers

Number of MV panels / switchgear sections

B — Soil data

Soil resistivity must be a measured or clearly stated design value. A uniform-soil calculation is approximate when the site is layered.

Soil model

Soil resistivity ρ (design value) (Ω·m)

Measured value used for the grid calculation. Must be greater than zero.

Surface-layer resistivity ρs (Ω·m)

Crushed rock / gravel surfacing. Enter 0 only if there is genuinely no surface layer.

Surface-layer thickness hs (m)

Grid burial depth h (m)

Seasonal / dry-condition resistivity (Ω·m)

Optional. If entered and higher than ρ, the design is also screened against it.

Soil-test reference

C — Fault data

Grid current is IG = If × Sf × Df. The full fault current is not used as grid current when a valid division factor is given.

System fault current If (kA)

Maximum earth-fault current (kA)

Used for conductor thermal sizing when higher than the split grid current.

Fault type

Fault duration tc (thermal) (s)

Shock duration ts (safety) (s)

Body shock duration used for tolerable touch and step voltage. Often shorter than tc.

Breaker interruption time (s)

Protection relay operating time (s)

Fault-current division factor Sf

Portion of the fault current returning through the earth grid. IG = If × Sf.

Decrement factor Df

Asymmetry allowance. 1.0 disables it.

X/R ratio

Future fault-current margin (%)

D — Earth grid geometry

Grid length Lx (m)

Grid width Ly (m)

Grid conductor spacing D (m)

Additional interconnection conductor length (m)

Peripheral conductor included

Internal mesh included

E — Solar array / MMS earthing

Earth-pit quantity is calculated from the array perimeter, the spacing criterion and the equipment connection points — never assumed.

Array field length (m)

Array field width (m)

Number of MMS / table blocks

Bonding conductor per MMS block (m)

Average run to bond one table row into the array grid.

Maximum spacing between earth connections (m)

Project design criterion — not an IEEE 80 equation.

Array perimeter grid material

Array perimeter grid depth (m)

F — Earth electrode / earth pits

Electrode type

Electrode diameter (mm)

Electrode length (m)

Electrode / rod quantity in the grid

Electrode spacing (m)

Soil enhancement treatment

G — Main earth grid conductor sizing

Main grid conductor material

Conductor sizing method

Initial / ambient conductor temperature (°C)

Maximum allowable conductor temperature (°C)

Leave 0 to use the IEEE 80 material fusing / limit temperature.

Design margin on conductor area (%)

Main grid conductor size

H — Transformer earthing

Body (equipment) earthing and neutral (system) earthing are calculated and reported separately.

Transformer rating (MVA)

Transformer earth-fault current (kA)

Transformer fault duration (s)

Transformer body earthing material

Transformer body conductor size

Transformer neutral earthing material

Transformer neutral conductor size

Body earth connections per transformer

Neutral earth connections per transformer

Transformer-to-grid connection length (m)

I — Inverter / MV panel / equipment earthing

RMU / VCB units

Lightning arrester sets

CT / PT units

Cable tray run length (m)

Boundary fence length (m)

Number of gates

Maximum fence earth-connection spacing (m)

J — Design criteria & optimisation

Project grid-resistance criterion (Ω)

Project / AHJ criterion only. It is never used on its own to declare the design safe.

Body weight assumption (kg)

IEEE 80 tolerable-voltage body criterion: 50 kg (0.116) or 70 kg (0.157).

Auto-optimise earthing design

How to use this calculator: Solar Plant Earthing Design Calculator

1Confirm that the Solar Plant Earthing Design Calculator matches the quantity or design check you need.
2Enter Plant capacity, DC capacity, and Evacuation / system voltage using the units printed beside each field.
3Select the applicable Plant type, System type, and Soil model options; these choices change the calculation method or factors.
4Calculate, then follow the substituted equations in the worked example and compare the result with any stated limit.
5Read the assumptions, warnings and cited references before using the result for a financial, medical or engineering decision.

Input guide and example values

Use values from the same measurement basis and time period. Conditional fields appear only when the related option is selected.

Input	Example value	Why it matters
Project name	Solar PV Plant	Optional input; leave the supplied default only when it matches your case.
Plant capacity	6 MW AC	Optional input; leave the supplied default only when it matches your case.
DC capacity	7.5 MWp	Optional input; leave the supplied default only when it matches your case.
Plant type	Ground-mounted	Select the option that matches the real installation or scenario.
System type	MV (1–36 kV)	Select the option that matches the real installation or scenario.
Evacuation / system voltage	33 kV	Measured or known evacuation / system voltage used by the calculation engine.
System frequency	50 Hz	Measured or known system frequency used by the calculation engine.
Number of inverter stations	4	Measured or known number of inverter stations used by the calculation engine.
Number of transformers	2	Measured or known number of transformers used by the calculation engine.
Number of MV panels / switchgear sections	3	Measured or known number of mv panels / switchgear sections used by the calculation engine.
Soil model	Uniform soil	Select the option that matches the real installation or scenario.
Soil resistivity ρ (design value)	10 Ω·m	Measured value used for the grid calculation. Must be greater than zero.
Surface-layer resistivity ρs	3000 Ω·m	Crushed rock / gravel surfacing. Enter 0 only if there is genuinely no surface layer.
Surface-layer thickness hs	0.1 m	Measured or known surface-layer thickness hs used by the calculation engine.
Grid burial depth h	0.6 m	Measured or known grid burial depth h used by the calculation engine.
Seasonal / dry-condition resistivity	0 Ω·m	Optional. If entered and higher than ρ, the design is also screened against it.
Soil-test reference	Wenner 4-pin test	Select the option that matches the real installation or scenario.
System fault current If	25 kA	Measured or known system fault current if used by the calculation engine.
Maximum earth-fault current	25 kA	Used for conductor thermal sizing when higher than the split grid current.
Fault type	Single line-to-ground	Select the option that matches the real installation or scenario.
Fault duration tc (thermal)	1 s	Measured or known fault duration tc (thermal) used by the calculation engine.
Shock duration ts (safety)	0.5 s	Body shock duration used for tolerable touch and step voltage. Often shorter than tc.
Breaker interruption time	0.06 s	Optional input; leave the supplied default only when it matches your case.
Protection relay operating time	0.3 s	Optional input; leave the supplied default only when it matches your case.
Fault-current division factor Sf	0.7	Portion of the fault current returning through the earth grid. IG = If × Sf.
Decrement factor Df	1	Asymmetry allowance. 1.0 disables it.
X/R ratio	10	Optional input; leave the supplied default only when it matches your case.
Future fault-current margin	0 %	Optional input; leave the supplied default only when it matches your case.
Grid length Lx	70 m	Measured or known grid length lx used by the calculation engine.
Grid width Ly	50 m	Measured or known grid width ly used by the calculation engine.
Grid conductor spacing D	5 m	Measured or known grid conductor spacing d used by the calculation engine.
Additional interconnection conductor length	0 m	Optional input; leave the supplied default only when it matches your case.
Peripheral conductor included	Yes — closed peripheral loop	Select the option that matches the real installation or scenario.
Internal mesh included	Yes — internal mesh conductors	Select the option that matches the real installation or scenario.
Array field length	300 m	Measured or known array field length used by the calculation engine.
Array field width	200 m	Measured or known array field width used by the calculation engine.
Number of MMS / table blocks	60	Measured or known number of mms / table blocks used by the calculation engine.
Bonding conductor per MMS block	12 m	Average run to bond one table row into the array grid.
Maximum spacing between earth connections	30 m	Project design criterion — not an IEEE 80 equation.
Array perimeter grid material	GI flat	Select the option that matches the real installation or scenario.
Array perimeter grid depth	0.6 m	Measured or known array perimeter grid depth used by the calculation engine.
Electrode type	GI pipe electrode	Select the option that matches the real installation or scenario.
Electrode diameter	40 mm	Measured or known electrode diameter used by the calculation engine.
Electrode length	3 m	Measured or known electrode length used by the calculation engine.
Electrode / rod quantity in the grid	12	Measured or known electrode / rod quantity in the grid used by the calculation engine.
Electrode spacing	6 m	Measured or known electrode spacing used by the calculation engine.
Soil enhancement treatment	None — natural backfill	Select the option that matches the real installation or scenario.
Main grid conductor material	GI / zinc-coated steel	Select the option that matches the real installation or scenario.
Conductor sizing method	IEEE 80 thermal equation (eq. 37)	Select the option that matches the real installation or scenario.
Initial / ambient conductor temperature	40 °C	Measured or known initial / ambient conductor temperature used by the calculation engine.
Maximum allowable conductor temperature	0 °C	Leave 0 to use the IEEE 80 material fusing / limit temperature.
Design margin on conductor area	30 %	Measured or known design margin on conductor area used by the calculation engine.
Main grid conductor size	Auto — smallest standard size that passes	Select the option that matches the real installation or scenario.
Transformer rating	6.5 MVA	Optional input; leave the supplied default only when it matches your case.
Transformer earth-fault current	25 kA	Measured or known transformer earth-fault current used by the calculation engine.
Transformer fault duration	1 s	Measured or known transformer fault duration used by the calculation engine.
Transformer body earthing material	GI flat	Select the option that matches the real installation or scenario.
Transformer body conductor size	Auto — smallest standard size that passes	Select the option that matches the real installation or scenario.
Transformer neutral earthing material	Copper flat	Select the option that matches the real installation or scenario.
Transformer neutral conductor size	Auto — smallest standard size that passes	Select the option that matches the real installation or scenario.
Body earth connections per transformer	2	Measured or known body earth connections per transformer used by the calculation engine.
Neutral earth connections per transformer	2	Measured or known neutral earth connections per transformer used by the calculation engine.
Transformer-to-grid connection length	10 m	Optional input; leave the supplied default only when it matches your case.
RMU / VCB units	2	Optional input; leave the supplied default only when it matches your case.
Lightning arrester sets	3	Optional input; leave the supplied default only when it matches your case.
CT / PT units	6	Optional input; leave the supplied default only when it matches your case.
Cable tray run length	400 m	Optional input; leave the supplied default only when it matches your case.
Boundary fence length	1000 m	Optional input; leave the supplied default only when it matches your case.
Number of gates	2	Optional input; leave the supplied default only when it matches your case.
Maximum fence earth-connection spacing	50 m	Optional input; leave the supplied default only when it matches your case.
Project grid-resistance criterion	1 Ω	Project / AHJ criterion only. It is never used on its own to declare the design safe.
Body weight assumption	50 kg	IEEE 80 tolerable-voltage body criterion: 50 kg (0.116) or 70 kg (0.157).
Auto-optimise earthing design	No — evaluate my configuration as entered	Select the option that matches the real installation or scenario.

Formula inputs & variables for Solar Plant Earthing Design Calculator

These are the named quantities used by this calculator. When the source formula does not define a mathematical symbol, OneCalcApp keeps the real input label instead of inventing one.

Variable / input	Unit	Meaning in this calculation
Project name	—	Optional input; leave the supplied default only when it matches your case.
Plant capacity	MW AC	Optional input; leave the supplied default only when it matches your case.
DC capacity	MWp	Optional input; leave the supplied default only when it matches your case.
Plant type	—	Select the option that matches the real installation or scenario.
System type	—	Select the option that matches the real installation or scenario.
Evacuation / system voltage	kV	Measured or known evacuation / system voltage used by the calculation engine.
System frequency	Hz	Measured or known system frequency used by the calculation engine.
Number of inverter stations	—	Measured or known number of inverter stations used by the calculation engine.

How the Solar Plant Earthing Design Calculator works

The Solar Plant Earthing Design Calculator uses Project name, Plant capacity, DC capacity, Plant type, System type, Evacuation / system voltage, System frequency, Number of inverter stations, Number of transformers, Number of MV panels / switchgear sections, Soil model, Soil resistivity ρ (design value), Surface-layer resistivity ρs, Surface-layer thickness hs, Grid burial depth h, Seasonal / dry-condition resistivity, Soil-test reference, System fault current If, Maximum earth-fault current, Fault type, Fault duration tc (thermal), Shock duration ts (safety), Breaker interruption time, Protection relay operating time, Fault-current division factor Sf, Decrement factor Df, X/R ratio, Future fault-current margin, Grid length Lx, Grid width Ly, Grid conductor spacing D, Additional interconnection conductor length, Peripheral conductor included, Internal mesh included, Array field length, Array field width, Number of MMS / table blocks, Bonding conductor per MMS block, Maximum spacing between earth connections, Array perimeter grid material, Array perimeter grid depth, Electrode type, Electrode diameter, Electrode length, Electrode / rod quantity in the grid, Electrode spacing, Soil enhancement treatment, Main grid conductor material, Conductor sizing method, Initial / ambient conductor temperature, Maximum allowable conductor temperature, Design margin on conductor area, Main grid conductor size, Transformer rating, Transformer earth-fault current, Transformer fault duration, Transformer body earthing material, Transformer body conductor size, Transformer neutral earthing material, Transformer neutral conductor size, Body earth connections per transformer, Neutral earth connections per transformer, Transformer-to-grid connection length, RMU / VCB units, Lightning arrester sets, CT / PT units, Cable tray run length, Boundary fence length, Number of gates, Maximum fence earth-connection spacing, Project grid-resistance criterion, Body weight assumption, and Auto-optimise earthing design to calculate Overall earthing design status, Main grid conductor — required area, Main grid conductor — selected, Total buried grid conductor length, Grid conductor spacing, Array perimeter conductor length, Total array earthing conductor, Earth pits required, Electrodes in the grid model, System fault current If, Fault-current division factor Sf, Grid current IG, Grid resistance Rg, Ground potential rise (GPR), Tolerable touch voltage, Attainable mesh (touch) voltage, Tolerable step voltage, Attainable step voltage, Transformer body earthing conductor, Transformer neutral earthing conductor, and Equipment earthing connection points. Its engine applies A = I / √[ (TCAP·10⁻⁴ / (tc·αr·ρr)) · ln((K₀+Tm)/(K₀+Ta)) ] (IEEE 80 eq. 37); the worked values below come from that same live calculation rather than a separately typed example.

With Project name Solar PV Plant, Plant capacity 6 MW AC, DC capacity 7.5 MWp, Plant type Ground-mounted, System type MV (1–36 kV), Evacuation / system voltage 33 kV, System frequency 50 Hz, Number of inverter stations 4, Number of transformers 2, Number of MV panels / switchgear sections 3, Soil model Uniform soil, Soil resistivity ρ (design value) 10 Ω·m, Surface-layer resistivity ρs 3000 Ω·m, Surface-layer thickness hs 0.1 m, Grid burial depth h 0.6 m, Seasonal / dry-condition resistivity 0 Ω·m, Soil-test reference Wenner 4-pin test, System fault current If 25 kA, Maximum earth-fault current 25 kA, Fault type Single line-to-ground, Fault duration tc (thermal) 1 s, Shock duration ts (safety) 0.5 s, Breaker interruption time 0.06 s, Protection relay operating time 0.3 s, Fault-current division factor Sf 0.7, Decrement factor Df 1, X/R ratio 10, Future fault-current margin 0 %, Grid length Lx 70 m, Grid width Ly 50 m, Grid conductor spacing D 5 m, Additional interconnection conductor length 0 m, Peripheral conductor included Yes — closed peripheral loop, Internal mesh included Yes — internal mesh conductors, Array field length 300 m, Array field width 200 m, Number of MMS / table blocks 60, Bonding conductor per MMS block 12 m, Maximum spacing between earth connections 30 m, Array perimeter grid material GI flat, Array perimeter grid depth 0.6 m, Electrode type GI pipe electrode, Electrode diameter 40 mm, Electrode length 3 m, Electrode / rod quantity in the grid 12, Electrode spacing 6 m, Soil enhancement treatment None — natural backfill, Main grid conductor material GI / zinc-coated steel, Conductor sizing method IEEE 80 thermal equation (eq. 37), Initial / ambient conductor temperature 40 °C, Maximum allowable conductor temperature 0 °C, Design margin on conductor area 30 %, Main grid conductor size Auto — smallest standard size that passes, Transformer rating 6.5 MVA, Transformer earth-fault current 25 kA, Transformer fault duration 1 s, Transformer body earthing material GI flat, Transformer body conductor size Auto — smallest standard size that passes, Transformer neutral earthing material Copper flat, Transformer neutral conductor size Auto — smallest standard size that passes, Body earth connections per transformer 2, Neutral earth connections per transformer 2, Transformer-to-grid connection length 10 m, RMU / VCB units 2, Lightning arrester sets 3, CT / PT units 6, Cable tray run length 400 m, Boundary fence length 1000 m, Number of gates 2, Maximum fence earth-connection spacing 50 m, Project grid-resistance criterion 1 Ω, Body weight assumption 50 kg, and Auto-optimise earthing design No — evaluate my configuration as entered, the main worked-example result is Overall earthing design status = REVIEW.

How each Solar Plant Earthing Design Calculator input is used

Project name

The Solar Plant Earthing Design Calculator worked example uses Project name = Solar PV Plant. This value is passed directly into the calculation.

Plant capacity

The Solar Plant Earthing Design Calculator worked example uses Plant capacity = 6 MW AC. This value is passed directly into the calculation, with an allowed minimum 0.

DC capacity

The Solar Plant Earthing Design Calculator worked example uses DC capacity = 7.5 MWp. This value is passed directly into the calculation, with an allowed minimum 0.

Plant type

The Solar Plant Earthing Design Calculator worked example selects “Ground-mounted”. Available choices include Ground-mounted, Rooftop / large commercial, and Hybrid / other. This selection may change the method or factor used by the engine, so choose the option that matches the real case.

System type

The Solar Plant Earthing Design Calculator worked example selects “MV (1–36 kV)”. Available choices include LV (≤ 1 kV), MV (1–36 kV), and HV (> 36 kV). This selection may change the method or factor used by the engine, so choose the option that matches the real case.

Evacuation / system voltage

The Solar Plant Earthing Design Calculator worked example uses Evacuation / system voltage = 33 kV. This value is passed directly into the calculation, with an allowed minimum 0.4.

System frequency

The Solar Plant Earthing Design Calculator worked example uses System frequency = 50 Hz. This value is passed directly into the calculation, with an allowed minimum 40 and maximum 70.

Number of inverter stations

The Solar Plant Earthing Design Calculator worked example uses Number of inverter stations = 4. This value is passed directly into the calculation, with an allowed minimum 0.

Number of transformers

The Solar Plant Earthing Design Calculator worked example uses Number of transformers = 2. This value is passed directly into the calculation, with an allowed minimum 0.

Number of MV panels / switchgear sections

The Solar Plant Earthing Design Calculator worked example uses Number of MV panels / switchgear sections = 3. This value is passed directly into the calculation, with an allowed minimum 0.

Soil model

The Solar Plant Earthing Design Calculator worked example selects “Uniform soil”. Available choices include Uniform soil, Two-layer soil, and Multilayer soil. This selection may change the method or factor used by the engine, so choose the option that matches the real case.

Soil resistivity ρ (design value)

The Solar Plant Earthing Design Calculator worked example uses Soil resistivity ρ (design value) = 10 Ω·m. This value is passed directly into the calculation, with an allowed minimum 0.1. Measured value used for the grid calculation. Must be greater than zero.

Surface-layer resistivity ρs

The Solar Plant Earthing Design Calculator worked example uses Surface-layer resistivity ρs = 3000 Ω·m. This value is passed directly into the calculation, with an allowed minimum 0. Crushed rock / gravel surfacing. Enter 0 only if there is genuinely no surface layer.

Surface-layer thickness hs

The Solar Plant Earthing Design Calculator worked example uses Surface-layer thickness hs = 0.1 m. This value is passed directly into the calculation, with an allowed minimum 0 and maximum 1.

Grid burial depth h

The Solar Plant Earthing Design Calculator worked example uses Grid burial depth h = 0.6 m. This value is passed directly into the calculation, with an allowed minimum 0.1 and maximum 3.

Seasonal / dry-condition resistivity

The Solar Plant Earthing Design Calculator worked example uses Seasonal / dry-condition resistivity = 0 Ω·m. This value is passed directly into the calculation, with an allowed minimum 0. Optional. If entered and higher than ρ, the design is also screened against it.

Soil-test reference

The Solar Plant Earthing Design Calculator worked example selects “Wenner 4-pin test”. Available choices include Wenner 4-pin test, Schlumberger test, and Assumed / not yet measured. This selection may change the method or factor used by the engine, so choose the option that matches the real case.

System fault current If

The Solar Plant Earthing Design Calculator worked example uses System fault current If = 25 kA. This value is passed directly into the calculation, with an allowed minimum 0.01.

Maximum earth-fault current

The Solar Plant Earthing Design Calculator worked example uses Maximum earth-fault current = 25 kA. This value is passed directly into the calculation, with an allowed minimum 0.01. Used for conductor thermal sizing when higher than the split grid current.

Fault type

The Solar Plant Earthing Design Calculator worked example selects “Single line-to-ground”. Available choices include Single line-to-ground, Double line-to-ground, and Other / as per system study. This selection may change the method or factor used by the engine, so choose the option that matches the real case.

Fault duration tc (thermal)

The Solar Plant Earthing Design Calculator worked example uses Fault duration tc (thermal) = 1 s. This value is passed directly into the calculation, with an allowed minimum 0.05 and maximum 10.

Shock duration ts (safety)

The Solar Plant Earthing Design Calculator worked example uses Shock duration ts (safety) = 0.5 s. This value is passed directly into the calculation, with an allowed minimum 0.05 and maximum 3. Body shock duration used for tolerable touch and step voltage. Often shorter than tc.

Breaker interruption time

The Solar Plant Earthing Design Calculator worked example uses Breaker interruption time = 0.06 s. This value is passed directly into the calculation, with an allowed minimum 0.

Protection relay operating time

The Solar Plant Earthing Design Calculator worked example uses Protection relay operating time = 0.3 s. This value is passed directly into the calculation, with an allowed minimum 0.

Fault-current division factor Sf

The Solar Plant Earthing Design Calculator worked example uses Fault-current division factor Sf = 0.7. This value is passed directly into the calculation, with an allowed minimum 0.01 and maximum 1. Portion of the fault current returning through the earth grid. IG = If × Sf.

Decrement factor Df

The Solar Plant Earthing Design Calculator worked example uses Decrement factor Df = 1. This value is passed directly into the calculation, with an allowed minimum 1 and maximum 1.6. Asymmetry allowance. 1.0 disables it.

X/R ratio

The Solar Plant Earthing Design Calculator worked example uses X/R ratio = 10. This value is passed directly into the calculation, with an allowed minimum 0.

Future fault-current margin

The Solar Plant Earthing Design Calculator worked example uses Future fault-current margin = 0 %. This value is passed directly into the calculation, with an allowed minimum 0 and maximum 100.

Grid length Lx

The Solar Plant Earthing Design Calculator worked example uses Grid length Lx = 70 m. This value is passed directly into the calculation, with an allowed minimum 1.

Grid width Ly

The Solar Plant Earthing Design Calculator worked example uses Grid width Ly = 50 m. This value is passed directly into the calculation, with an allowed minimum 1.

Grid conductor spacing D

The Solar Plant Earthing Design Calculator worked example uses Grid conductor spacing D = 5 m. This value is passed directly into the calculation, with an allowed minimum 0.5 and maximum 40.

Additional interconnection conductor length

The Solar Plant Earthing Design Calculator worked example uses Additional interconnection conductor length = 0 m. This value is passed directly into the calculation, with an allowed minimum 0.

Peripheral conductor included

The Solar Plant Earthing Design Calculator worked example selects “Yes — closed peripheral loop”. Available choices include Yes — closed peripheral loop and No. This selection may change the method or factor used by the engine, so choose the option that matches the real case.

Internal mesh included

The Solar Plant Earthing Design Calculator worked example selects “Yes — internal mesh conductors”. Available choices include Yes — internal mesh conductors and No. This selection may change the method or factor used by the engine, so choose the option that matches the real case.

Array field length

The Solar Plant Earthing Design Calculator worked example uses Array field length = 300 m. This value is passed directly into the calculation, with an allowed minimum 0.

Array field width

The Solar Plant Earthing Design Calculator worked example uses Array field width = 200 m. This value is passed directly into the calculation, with an allowed minimum 0.

Number of MMS / table blocks

The Solar Plant Earthing Design Calculator worked example uses Number of MMS / table blocks = 60. This value is passed directly into the calculation, with an allowed minimum 0.

Bonding conductor per MMS block

The Solar Plant Earthing Design Calculator worked example uses Bonding conductor per MMS block = 12 m. This value is passed directly into the calculation, with an allowed minimum 0. Average run to bond one table row into the array grid.

Maximum spacing between earth connections

The Solar Plant Earthing Design Calculator worked example uses Maximum spacing between earth connections = 30 m. This value is passed directly into the calculation, with an allowed minimum 2. Project design criterion — not an IEEE 80 equation.

Array perimeter grid material

The Solar Plant Earthing Design Calculator worked example selects “GI flat”. Available choices include GI flat, Copper flat, and Aluminium flat. This selection may change the method or factor used by the engine, so choose the option that matches the real case.

Array perimeter grid depth

The Solar Plant Earthing Design Calculator worked example uses Array perimeter grid depth = 0.6 m. This value is passed directly into the calculation, with an allowed minimum 0.1 and maximum 3.

Electrode type

The Solar Plant Earthing Design Calculator worked example selects “GI pipe electrode”. Available choices include GI pipe electrode, GI rod electrode, Copper / copper-bonded rod, and Chemical earth electrode. This selection may change the method or factor used by the engine, so choose the option that matches the real case.

Electrode diameter

The Solar Plant Earthing Design Calculator worked example uses Electrode diameter = 40 mm. This value is passed directly into the calculation, with an allowed minimum 5.

Electrode length

The Solar Plant Earthing Design Calculator worked example uses Electrode length = 3 m. This value is passed directly into the calculation, with an allowed minimum 0.5.

Electrode / rod quantity in the grid

The Solar Plant Earthing Design Calculator worked example uses Electrode / rod quantity in the grid = 12. This value is passed directly into the calculation, with an allowed minimum 0.

Electrode spacing

The Solar Plant Earthing Design Calculator worked example uses Electrode spacing = 6 m. This value is passed directly into the calculation, with an allowed minimum 0.5.

Soil enhancement treatment

The Solar Plant Earthing Design Calculator worked example selects “None — natural backfill”. Available choices include None — natural backfill, Bentonite backfill, and Chemical earthing compound. This selection may change the method or factor used by the engine, so choose the option that matches the real case.

Main grid conductor material

The Solar Plant Earthing Design Calculator worked example selects “GI / zinc-coated steel”. Available choices include GI / zinc-coated steel, Copper, Aluminium, and Steel (bare). This selection may change the method or factor used by the engine, so choose the option that matches the real case.

Conductor sizing method

The Solar Plant Earthing Design Calculator worked example selects “IEEE 80 thermal equation (eq. 37)”. Available choices include IEEE 80 thermal equation (eq. 37) and IS 3043 / CBIP k-factor: A = I√t / k. This selection may change the method or factor used by the engine, so choose the option that matches the real case.

Initial / ambient conductor temperature

The Solar Plant Earthing Design Calculator worked example uses Initial / ambient conductor temperature = 40 °C. This value is passed directly into the calculation, with an allowed minimum -10 and maximum 90.

Maximum allowable conductor temperature

The Solar Plant Earthing Design Calculator worked example uses Maximum allowable conductor temperature = 0 °C. This value is passed directly into the calculation, with an allowed minimum 0. Leave 0 to use the IEEE 80 material fusing / limit temperature.

Design margin on conductor area

The Solar Plant Earthing Design Calculator worked example uses Design margin on conductor area = 30 %. This value is passed directly into the calculation, with an allowed minimum 0 and maximum 100.

Main grid conductor size

The Solar Plant Earthing Design Calculator worked example selects “Auto — smallest standard size that passes”. Available choices include Auto — smallest standard size that passes, 25 × 3 mm (75 mm²), 25 × 6 mm (150 mm²), 32 × 6 mm (192 mm²), and 40 × 6 mm (240 mm²). This selection may change the method or factor used by the engine, so choose the option that matches the real case.

Transformer rating

The Solar Plant Earthing Design Calculator worked example uses Transformer rating = 6.5 MVA. This value is passed directly into the calculation, with an allowed minimum 0.

Transformer earth-fault current

The Solar Plant Earthing Design Calculator worked example uses Transformer earth-fault current = 25 kA. This value is passed directly into the calculation, with an allowed minimum 0.01.

Transformer fault duration

The Solar Plant Earthing Design Calculator worked example uses Transformer fault duration = 1 s. This value is passed directly into the calculation, with an allowed minimum 0.05 and maximum 10.

Transformer body earthing material

The Solar Plant Earthing Design Calculator worked example selects “GI flat”. Available choices include GI flat and Copper flat. This selection may change the method or factor used by the engine, so choose the option that matches the real case.

Transformer body conductor size

Transformer neutral earthing material

The Solar Plant Earthing Design Calculator worked example selects “Copper flat”. Available choices include Copper flat and GI flat. This selection may change the method or factor used by the engine, so choose the option that matches the real case.

Transformer neutral conductor size

Body earth connections per transformer

The Solar Plant Earthing Design Calculator worked example uses Body earth connections per transformer = 2. This value is passed directly into the calculation, with an allowed minimum 0.

Neutral earth connections per transformer

The Solar Plant Earthing Design Calculator worked example uses Neutral earth connections per transformer = 2. This value is passed directly into the calculation, with an allowed minimum 0.

Transformer-to-grid connection length

The Solar Plant Earthing Design Calculator worked example uses Transformer-to-grid connection length = 10 m. This value is passed directly into the calculation, with an allowed minimum 0.

RMU / VCB units

The Solar Plant Earthing Design Calculator worked example uses RMU / VCB units = 2. This value is passed directly into the calculation, with an allowed minimum 0.

Lightning arrester sets

The Solar Plant Earthing Design Calculator worked example uses Lightning arrester sets = 3. This value is passed directly into the calculation, with an allowed minimum 0.

CT / PT units

The Solar Plant Earthing Design Calculator worked example uses CT / PT units = 6. This value is passed directly into the calculation, with an allowed minimum 0.

Cable tray run length

The Solar Plant Earthing Design Calculator worked example uses Cable tray run length = 400 m. This value is passed directly into the calculation, with an allowed minimum 0.

Boundary fence length

The Solar Plant Earthing Design Calculator worked example uses Boundary fence length = 1000 m. This value is passed directly into the calculation, with an allowed minimum 0.

Number of gates

The Solar Plant Earthing Design Calculator worked example uses Number of gates = 2. This value is passed directly into the calculation, with an allowed minimum 0.

Maximum fence earth-connection spacing

The Solar Plant Earthing Design Calculator worked example uses Maximum fence earth-connection spacing = 50 m. This value is passed directly into the calculation, with an allowed minimum 5.

Project grid-resistance criterion

The Solar Plant Earthing Design Calculator worked example uses Project grid-resistance criterion = 1 Ω. This value is passed directly into the calculation, with an allowed minimum 0.01. Project / AHJ criterion only. It is never used on its own to declare the design safe.

Body weight assumption

The Solar Plant Earthing Design Calculator worked example uses Body weight assumption = 50 kg. This value is passed directly into the calculation, with an allowed minimum 50 and maximum 70. IEEE 80 tolerable-voltage body criterion: 50 kg (0.116) or 70 kg (0.157).

Auto-optimise earthing design

The Solar Plant Earthing Design Calculator worked example selects “No — evaluate my configuration as entered”. Available choices include No — evaluate my configuration as entered and Yes — tighten spacing / add rods until the safety checks pass. This selection may change the method or factor used by the engine, so choose the option that matches the real case.

Solar Plant Earthing Design Calculator formulas and result interpretation

Formula 1: relationship used

In the Solar Plant Earthing Design Calculator, A = I / √[ (TCAP·10⁻⁴ / (tc·αr·ρr)) · ln((K₀+Tm)/(K₀+Ta)) ] (IEEE 80 eq. 37). The quantities in this relationship come from the named inputs or from an earlier calculation step shown in the worked example.

Formula 2: relationship used

In the Solar Plant Earthing Design Calculator, IG = If × Sf × Df. The quantities in this relationship come from the named inputs or from an earlier calculation step shown in the worked example.

Formula 3: relationship used

In the Solar Plant Earthing Design Calculator, Lc = n_A·Lx + n_B·Ly ; LM = Lc + [1.55 + 1.22(Lr/√(Lx²+Ly²))]·LR ; LS = 0.75Lc + 0.85LR. The quantities in this relationship come from the named inputs or from an earlier calculation step shown in the worked example.

Formula 4: relationship used

In the Solar Plant Earthing Design Calculator, R₁, R₂, Rm by Schwarz ; Rg = (R₁R₂ − Rm²)/(R₁ + R₂ − 2Rm). The quantities in this relationship come from the named inputs or from an earlier calculation step shown in the worked example.

Formula 5: relationship used

In the Solar Plant Earthing Design Calculator, GPR = IG × Rg. The quantities in this relationship come from the named inputs or from an earlier calculation step shown in the worked example.

Formula 6: relationship used

In the Solar Plant Earthing Design Calculator, Cs = 1 − 0.09(1 − ρ/ρs)/(2hs + 0.09). The quantities in this relationship come from the named inputs or from an earlier calculation step shown in the worked example.

Formula 7: relationship used

In the Solar Plant Earthing Design Calculator, E_touch = (1000 + 1.5·Cs·ρs)·0.116/√ts ; E_step = (1000 + 6·Cs·ρs)·0.116/√ts (50 kg). The quantities in this relationship come from the named inputs or from an earlier calculation step shown in the worked example.

Formula 8: relationship used

In the Solar Plant Earthing Design Calculator, Em = ρ·IG·Km·Ki / LM ; Es = ρ·IG·Ks·Ki / LS. The quantities in this relationship come from the named inputs or from an earlier calculation step shown in the worked example.

Overall earthing design status

For the displayed Solar Plant Earthing Design Calculator worked example, Overall earthing design status is REVIEW. mathematically complete — design criteria need confirmation Verify Project name, Plant capacity, and DC capacity and their units before relying on this output.

Main grid conductor — required area

For the displayed Solar Plant Earthing Design Calculator worked example, Main grid conductor — required area is 476.89 mm². 366.84 mm² theoretical + 30% margin Verify Project name, Plant capacity, and DC capacity and their units before relying on this output.

Main grid conductor — selected

For the displayed Solar Plant Earthing Design Calculator worked example, Main grid conductor — selected is 50 × 10 mm (500 mm²) GI / zinc-coated steel. 4.8% spare over the required area Verify Project name, Plant capacity, and DC capacity and their units before relying on this output.

Total buried grid conductor length

For the displayed Solar Plant Earthing Design Calculator worked example, Total buried grid conductor length is 1,520 m. 11 runs × 70 m + 15 runs × 50 m Verify Project name, Plant capacity, and DC capacity and their units before relying on this output.

Grid conductor spacing

For the displayed Solar Plant Earthing Design Calculator worked example, Grid conductor spacing is 5 m. grid 70 × 50 m, area 3,500 m² Verify Project name, Plant capacity, and DC capacity and their units before relying on this output.

Array perimeter conductor length

For the displayed Solar Plant Earthing Design Calculator worked example, Array perimeter conductor length is 1,000 m. 50 × 10 mm (500 mm²) GI / zinc-coated steel Verify Project name, Plant capacity, and DC capacity and their units before relying on this output.

Total array earthing conductor

For the displayed Solar Plant Earthing Design Calculator worked example, Total array earthing conductor is 1,720 m. perimeter 1,000 m + 60 block bonds 720 m Verify Project name, Plant capacity, and DC capacity and their units before relying on this output.

Earth pits required

For the displayed Solar Plant Earthing Design Calculator worked example, Earth pits required is 95 Nos. calculated minimum 95, spacing achieved 13.05 m Verify Project name, Plant capacity, and DC capacity and their units before relying on this output.

Electrodes in the grid model

For the displayed Solar Plant Earthing Design Calculator worked example, Electrodes in the grid model is 12 × 40 mm dia × 3 m. total electrode length 36 m Verify Project name, Plant capacity, and DC capacity and their units before relying on this output.

System fault current If

For the displayed Solar Plant Earthing Design Calculator worked example, System fault current If is 25 kA. as entered Verify Project name, Plant capacity, and DC capacity and their units before relying on this output.

Fault-current division factor Sf

For the displayed Solar Plant Earthing Design Calculator worked example, Fault-current division factor Sf is 0.7. no decrement factor applied Verify Project name, Plant capacity, and DC capacity and their units before relying on this output.

Grid current IG

For the displayed Solar Plant Earthing Design Calculator worked example, Grid current IG is 17.5 kA. IG = 25 × 0.7 × 1 Verify Project name, Plant capacity, and DC capacity and their units before relying on this output.

Grid resistance Rg

For the displayed Solar Plant Earthing Design Calculator worked example, Grid resistance Rg is 0.0798 Ω. R₁ = 0.0799 Ω, R₂ = 0.2748 Ω, Rm = 0.0764 Ω Verify Project name, Plant capacity, and DC capacity and their units before relying on this output.

Ground potential rise (GPR)

For the displayed Solar Plant Earthing Design Calculator worked example, Ground potential rise (GPR) is 1,396.91 V. 1.397 kV Verify Project name, Plant capacity, and DC capacity and their units before relying on this output.

Tolerable touch voltage

For the displayed Solar Plant Earthing Design Calculator worked example, Tolerable touch voltage is 673.93 V. 50 kg body, ts = 0.5 s, Cs = 0.6907 Verify Project name, Plant capacity, and DC capacity and their units before relying on this output.

Attainable mesh (touch) voltage

For the displayed Solar Plant Earthing Design Calculator worked example, Attainable mesh (touch) voltage is 120.85 V. margin 553.08 V Verify Project name, Plant capacity, and DC capacity and their units before relying on this output.

Tolerable step voltage

For the displayed Solar Plant Earthing Design Calculator worked example, Tolerable step voltage is 2,203.57 V. 50 kg body, ts = 0.5 s Verify Project name, Plant capacity, and DC capacity and their units before relying on this output.

Attainable step voltage

For the displayed Solar Plant Earthing Design Calculator worked example, Attainable step voltage is 146 V. margin 2,057.57 V Verify Project name, Plant capacity, and DC capacity and their units before relying on this output.

Transformer body earthing conductor

For the displayed Solar Plant Earthing Design Calculator worked example, Transformer body earthing conductor is 50 × 10 mm (500 mm²) GI / zinc-coated steel. required 476.89 mm², 2 connections per transformer Verify Project name, Plant capacity, and DC capacity and their units before relying on this output.

Transformer neutral earthing conductor

For the displayed Solar Plant Earthing Design Calculator worked example, Transformer neutral earthing conductor is 25 × 6 mm (150 mm²) Copper (annealed soft-drawn). required 115.31 mm², 2 connections per transformer Verify Project name, Plant capacity, and DC capacity and their units before relying on this output.

Equipment earthing connection points

For the displayed Solar Plant Earthing Design Calculator worked example, Equipment earthing connection points is 73 Nos. 4 inverters, 3 MV panels, 2 transformers, fence and trays Verify Project name, Plant capacity, and DC capacity and their units before relying on this output.

Solar Plant Earthing Design Calculator accuracy, checks and limitations

Solar Plant Earthing Design Calculator units check: confirm Project name, Plant capacity (MW AC), DC capacity (MWp), Plant type, System type, Evacuation / system voltage (kV), System frequency (Hz), Number of inverter stations, Number of transformers, Number of MV panels / switchgear sections, Soil model, Soil resistivity ρ (design value) (Ω·m), Surface-layer resistivity ρs (Ω·m), Surface-layer thickness hs (m), Grid burial depth h (m), Seasonal / dry-condition resistivity (Ω·m), Soil-test reference, System fault current If (kA), Maximum earth-fault current (kA), Fault type, Fault duration tc (thermal) (s), Shock duration ts (safety) (s), Breaker interruption time (s), Protection relay operating time (s), Fault-current division factor Sf, Decrement factor Df, X/R ratio, Future fault-current margin (%), Grid length Lx (m), Grid width Ly (m), Grid conductor spacing D (m), Additional interconnection conductor length (m), Peripheral conductor included, Internal mesh included, Array field length (m), Array field width (m), Number of MMS / table blocks, Bonding conductor per MMS block (m), Maximum spacing between earth connections (m), Array perimeter grid material, Array perimeter grid depth (m), Electrode type, Electrode diameter (mm), Electrode length (m), Electrode / rod quantity in the grid, Electrode spacing (m), Soil enhancement treatment, Main grid conductor material, Conductor sizing method, Initial / ambient conductor temperature (°C), Maximum allowable conductor temperature (°C), Design margin on conductor area (%), Main grid conductor size, Transformer rating (MVA), Transformer earth-fault current (kA), Transformer fault duration (s), Transformer body earthing material, Transformer body conductor size, Transformer neutral earthing material, Transformer neutral conductor size, Body earth connections per transformer, Neutral earth connections per transformer, Transformer-to-grid connection length (m), RMU / VCB units, Lightning arrester sets, CT / PT units, Cable tray run length (m), Boundary fence length (m), Number of gates, Maximum fence earth-connection spacing (m), Project grid-resistance criterion (Ω), Body weight assumption (kg), and Auto-optimise earthing design before calculating.
Solar Plant Earthing Design Calculator result check: compare Overall earthing design status, Main grid conductor — required area, Main grid conductor — selected, Total buried grid conductor length, Grid conductor spacing, Array perimeter conductor length, Total array earthing conductor, Earth pits required, Electrodes in the grid model, System fault current If, Fault-current division factor Sf, Grid current IG, Grid resistance Rg, Ground potential rise (GPR), Tolerable touch voltage, Attainable mesh (touch) voltage, Tolerable step voltage, Attainable step voltage, Transformer body earthing conductor, Transformer neutral earthing conductor, and Equipment earthing connection points with the substituted formula steps and the displayed rounding precision.
Solar Plant Earthing Design Calculator: Use this result for preliminary design and cross-checking. Confirm the applicable code edition, manufacturer data, site conditions and qualified-engineer approval before final design or installation.

Formula, derivation and worked example

A solar plant earthing design is not an earth-resistance calculation. The grid conductor must survive the fault thermally, the buried grid and its rods must produce a known resistance, the resulting ground potential rise must be assessed, and the attainable mesh (touch) and step voltages must be lower than the tolerable values a person can withstand for the shock duration. This calculator runs that full IEEE Std 80 chain for the main plant grid, then sizes the solar-array perimeter grid, earth pits, transformer body earthing, transformer neutral earthing and equipment bonding, and reports a single PASS / REVIEW / FAIL assessment based on every applicable check — never on grid resistance alone.

A = I / √[ (TCAP·10⁻⁴ / (tc·αr·ρr)) · ln((K₀+Tm)/(K₀+Ta)) ] (IEEE 80 eq. 37)

IG = If × Sf × Df

Lc = n_A·Lx + n_B·Ly ; LM = Lc + [1.55 + 1.22(Lr/√(Lx²+Ly²))]·LR ; LS = 0.75Lc + 0.85LR

R₁, R₂, Rm by Schwarz ; Rg = (R₁R₂ − Rm²)/(R₁ + R₂ − 2Rm)

GPR = IG × Rg

Cs = 1 − 0.09(1 − ρ/ρs)/(2hs + 0.09)

E_touch = (1000 + 1.5·Cs·ρs)·0.116/√ts ; E_step = (1000 + 6·Cs·ρs)·0.116/√ts (50 kg)

Em = ρ·IG·Km·Ki / LM ; Es = ρ·IG·Ks·Ki / LS

Substitution steps

1. Grid geometry
Lc = 11 × 70 + 15 × 50
= 1,520 m buried conductor
2. Grid area and perimeter
A = 70 × 50 ; Lp = 2(70 + 50)
= A = 3,500 m², Lp = 240 m, diagonal = 86.02 m
3. Conductor thermal sizing
A = 25 / √[(3.931·10⁻⁴ / (1 × 0.0032 × 20.1)) · ln((293+419)/(293+40))]
= 366.84 mm² required
4. Design margin applied
366.84 × (1 + 30%)
= 476.89 mm² → selected 50 × 10 mm (500 mm²)
5. Grid current
IG = 25 kA × 0.7 × 1
= 17.5 kA
6. Schwarz grid resistance R₁
R₁ = (ρ/πLc)[ln(2Lc/a′) + k₁Lc/√A − k₂], a′ = √(d·2h) = 0.2141 m, k₁ = 1.331, k₂ = 5.62
= 0.0799 Ω
7. Rod-bed resistance R₂
R₂ = (ρ/2πnLr)[ln(8Lr/d) − 1 + 2k₁Lr(√n − 1)²/√A], n = 12
= 0.2748 Ω (single rod 2.8632 Ω)
8. Mutual resistance Rm
Rm = (ρ/πLc)[ln(2Lc/Lr) + k₁Lc/√A − k₂ + 1]
= 0.0764 Ω
9. Combined grounding resistance Rg
Rg = (R₁R₂ − Rm²)/(R₁ + R₂ − 2Rm)
= 0.0798 Ω
10. Ground potential rise
GPR = 17,500 A × 0.0798 Ω
= 1,396.91 V = 1.397 kV
11. Surface-layer factor Cs
Cs = 1 − 0.09(1 − 10/3,000)/(2 × 0.1 + 0.09)
= 0.6907
12. Tolerable touch voltage
E_touch = (1000 + 1.5 × 0.6907 × 3,000) × 0.116/√0.5
= 673.93 V
13. Tolerable step voltage
E_step = (1000 + 6 × 0.6907 × 3,000) × 0.116/√0.5
= 2,203.57 V
14. Geometric factors
n = na·nb = 12.667 × 1.007 ; Km = 0.4302 ; Ki = 2.5319 ; Ks = 0.3857 ; Kh = 1.2649 ; Kii = 1
= n = 12.756
15. Effective lengths
LM = Lc + [1.55 + 1.22(Lr/√(Lx²+Ly²))]·LR ; LS = 0.75Lc + 0.85LR
= LM = 1,577.33 m, LS = 1,170.6 m
16. Attainable mesh voltage
Em = 10 × 17,500 × 0.4302 × 2.5319 / 1,577.33
= 120.85 V (tolerable 673.93 V) — SAFE
17. Attainable step voltage
Es = 10 × 17,500 × 0.3857 × 2.5319 / 1,170.6
= 146 V (tolerable 2,203.57 V) — SAFE
18. Earth-pit requirement
array perimeter 1,000/30 = 34 + grid perimeter 240/30 = 8 + 4 corners + 8 transformer + 8 inverter + 6 MV + 3 LA + 24 fence
= 95 minimum → 95 selected
19. Transformer body earthing
A = f(25 kA, 1 s, GI / zinc-coated steel) × (1 + 30%)
= 476.89 mm² → 50 × 10 mm (500 mm²), 2 connections
20. Transformer neutral earthing
A = f(25 kA, 1 s, Copper (annealed soft-drawn)) × (1 + 30%)
= 115.31 mm² → 25 × 6 mm (150 mm²), 2 connections

Computed example results

Overall earthing design status: REVIEW; mathematically complete — design criteria need confirmation
Main grid conductor — required area: 476.89 mm²; 366.84 mm² theoretical + 30% margin
Main grid conductor — selected: 50 × 10 mm (500 mm²) GI / zinc-coated steel; 4.8% spare over the required area
Total buried grid conductor length: 1,520 m; 11 runs × 70 m + 15 runs × 50 m
Grid conductor spacing: 5 m; grid 70 × 50 m, area 3,500 m²
Array perimeter conductor length: 1,000 m; 50 × 10 mm (500 mm²) GI / zinc-coated steel
Total array earthing conductor: 1,720 m; perimeter 1,000 m + 60 block bonds 720 m
Earth pits required: 95 Nos; calculated minimum 95, spacing achieved 13.05 m
Electrodes in the grid model: 12 × 40 mm dia × 3 m; total electrode length 36 m
System fault current If: 25 kA; as entered
Fault-current division factor Sf: 0.7; no decrement factor applied
Grid current IG: 17.5 kA; IG = 25 × 0.7 × 1
Grid resistance Rg: 0.0798 Ω; R₁ = 0.0799 Ω, R₂ = 0.2748 Ω, Rm = 0.0764 Ω
Ground potential rise (GPR): 1,396.91 V; 1.397 kV
Tolerable touch voltage: 673.93 V; 50 kg body, ts = 0.5 s, Cs = 0.6907
Attainable mesh (touch) voltage: 120.85 V; margin 553.08 V
Tolerable step voltage: 2,203.57 V; 50 kg body, ts = 0.5 s
Attainable step voltage: 146 V; margin 2,057.57 V
Transformer body earthing conductor: 50 × 10 mm (500 mm²) GI / zinc-coated steel; required 476.89 mm², 2 connections per transformer
Transformer neutral earthing conductor: 25 × 6 mm (150 mm²) Copper (annealed soft-drawn); required 115.31 mm², 2 connections per transformer
Equipment earthing connection points: 73 Nos; 4 inverters, 3 MV panels, 2 transformers, fence and trays

Understanding the result

Read the main result together with supporting checks, assumptions, limits and intermediate values.

For a manual check, repeat the first equation, confirm the units and change one input at a time.

Assumptions and calculation scope

Plant capacity is assumed to be entered in MW AC; converting from another unit before entry avoids changing the numerical meaning of the calculation.
Plant type is assumed to match the real case. Choosing a different available option can change the method, factor or interpretation used by this calculator.
Solar Plant Earthing Design Calculator applies the displayed A = I / √[ (TCAP·10⁻⁴ / (tc·αr·ρr)) · ln((K₀+Tm)/(K₀+Ta)) ] (IEEE 80 eq. 37) relationship to the entered solar inputs. Factors that are not exposed as inputs or stated assumptions are outside this calculator's calculation scope.

Common mistakes when using Solar Plant Earthing Design Calculator

Do not mix units for Plant capacity (MW AC), DC capacity (MWp), Evacuation / system voltage (kV). A unit mismatch changes the input magnitude even when the typed number looks reasonable.
Do not leave Plant type on the default choice unless that choice matches the real scenario; the selected option can change the calculation path or factor.
Do not replace the displayed A = I / √[ (TCAP·10⁻⁴ / (tc·αr·ρr)) · ln((K₀+Tm)/(K₀+Ta)) ] (IEEE 80 eq. 37) relationship with a different convention without also changing the underlying assumptions; compare like-for-like methods when checking the result.
Do not treat Overall earthing design status = REVIEW from the worked example as a universal answer. It belongs to the displayed example inputs and must be recalculated for the actual case.

When the Solar Plant Earthing Design Calculator is useful

Solar Plant Earthing Design Calculator is designed for cases where Project name, Plant capacity, DC capacity, Plant type are known and you need Overall earthing design status, Main grid conductor — required area, Main grid conductor — selected. The page keeps the live calculator, calculation method and worked example together so the result can be checked instead of treated as a black-box number.

Use the calculator for the scope described by its inputs and notes. The displayed method is A = I / √[ (TCAP·10⁻⁴ / (tc·αr·ρr)) · ln((K₀+Tm)/(K₀+Ta)) ] (IEEE 80 eq. 37). If the real project or decision needs factors that are not represented here, treat the result as an estimate and add the missing checks separately.

Project name and Plant capacity: what changes the answer

The worked example uses Project name = Solar PV Plant, Plant capacity = 6 MW AC, DC capacity = 7.5 MWp, Plant type = Ground-mounted. With those values, Overall earthing design status is REVIEW. Changing an input should be interpreted according to that field's unit, range, option and hint rather than by the number alone.

For this calculator, the main input roles are: Project name: Optional input; leave the supplied default only when it matches your case. Plant capacity (MW AC): Optional input; leave the supplied default only when it matches your case. DC capacity (MWp): Optional input; leave the supplied default only when it matches your case. Plant type: Select the option that matches the real installation or scenario. Available choices include Ground-mounted, Rooftop / large commercial, Hybrid / other.

How to sanity-check a Solar Plant Earthing Design Calculator result

Start by confirming the entered values and units, then compare the substituted working with the displayed formula or calculation steps. Pay particular attention to Overall earthing design status, because it is the first worked-example output shown by the live engine.

Finally, compare the result with the assumptions, warnings and related calculators on this page. A nearby calculator can be useful as a cross-check when it measures the same workflow from a different input or output direction.

Next logical calculator

Continue with Earthing Calculator

Earthing Calculator is directly connected from Solar Plant Earthing Design Calculator as a source-defined continuation or comparison.

Open Earthing Calculator

Standards, source trail and limitations

References show the method used. Check the current local edition, amendments and project specification before a regulated decision.

Formula

A = I / √[ (TCAP·10⁻⁴ / (tc·αr·ρr)) · ln((K₀+Tm)/(K₀+Ta)) ] (IEEE 80 eq. 37)
IG = If × Sf × Df
Lc = n_A·Lx + n_B·Ly ; LM = Lc + [1.55 + 1.22(Lr/√(Lx²+Ly²))]·LR ; LS = 0.75Lc + 0.85LR
R₁, R₂, Rm by Schwarz ; Rg = (R₁R₂ − Rm²)/(R₁ + R₂ − 2Rm)
GPR = IG × Rg
Cs = 1 − 0.09(1 − ρ/ρs)/(2hs + 0.09)
E_touch = (1000 + 1.5·Cs·ρs)·0.116/√ts ; E_step = (1000 + 6·Cs·ρs)·0.116/√ts (50 kg)
Em = ρ·IG·Km·Ki / LM ; Es = ρ·IG·Ks·Ki / LS

Engineering notes

Grid resistance below 1 Ω does not by itself make a grounding system safe. Safety is decided by touch and step voltage.
Transformer body earthing (equipment) and transformer neutral earthing (system) are different functions and are reported separately.
Earth-pit quantity depends on grid geometry, the spacing design criterion and the number of equipment connection points. A fixed number such as 4 or 10 pits is not an engineering answer.
A uniform-soil calculation is approximate on a layered site — a two-layer model or a soil investigation should govern the issued design.

Warnings

This calculator is a design aid. It does not replace a soil-resistivity investigation, a system fault study, approved drawings, utility/AHJ requirements or verification by a qualified electrical engineer.
Where project specifications, utility requirements, statutory regulations or applicable standards differ, the governing project/AHJ requirement shall take precedence.

Standards & references

IEEE Std 80-2013 and IEEE Std 80-2013/Cor 1-2015 — primary calculation methodology
CBIP Manual on Substation, Publication No. 223 — Indian substation earthing practice
IS 3043 — Code of practice for earthing
CEA (Measures relating to Safety and Electric Supply) Regulations, 2023 and amendments
IEC 62548-1 — PV arrays, design requirements including earthing provisions
IEC 60364-5-54 — Earthing arrangements and protective conductors
IEC 60364-7-712 — PV power supply installations
IEC 62305 series — Lightning protection and equipotential bonding
IEC 62446-1 — PV system documentation, commissioning tests and inspection

Frequently asked questions

What is solar plant earthing?

It is the buried conductor grid, electrodes and bonding network that gives fault current a controlled return path, holds all exposed metal at a common potential, and keeps touch and step voltages within limits a person can survive during an earth fault.

How is the solar earthing grid size calculated?

Grid conductor length comes from the grid dimensions and conductor spacing, the conductor cross-section comes from the fault current and fault duration through the IEEE 80 thermal equation, and the resulting grid is then verified against grid resistance, GPR, mesh voltage and step voltage.

How many earth pits are required for a solar power plant?

It is calculated, not assumed. Take the array and grid perimeter, divide by the maximum earth-connection spacing set in the design criterion, add corner points, then add the dedicated pits required for transformers, inverters, MV panels, lightning arresters and fence sections.

Is one earth pit enough for a solar plant?

No. Even a small plant needs a grid with multiple electrodes, and equipment such as transformers requires more than one independent connection. A single pit gives no redundancy and cannot control touch and step voltage across a plant.

What is the recommended earth grid conductor size?

There is no universal size. It follows from the earth-fault current, the fault duration, the conductor material and the applied design margin. The same plant at 1 s and 25 kA needs a far heavier conductor than at 0.5 s and 10 kA.

How is earthing conductor size calculated from fault current?

IEEE 80 eq. 37 gives A = I / √[(TCAP·10⁻⁴/(tc·αr·ρr))·ln((K₀+Tm)/(K₀+Ta))]. The IS 3043 / CBIP shortcut is A = I√t / k, where k depends on the material and the permitted temperature rise.

What is grid current in an earthing calculation?

Grid current IG is the portion of the earth-fault current that actually returns through the earth grid into the soil: IG = If × Sf × Df. It drives GPR, mesh voltage and step voltage.

What is the fault-current division factor?

Sf is the fraction of total earth-fault current that flows into the grid rather than returning through overhead earth wires, cable sheaths or neighbouring earthed structures. It is obtained from a current-division study — for example 25 kA × 0.7 = 17.5 kA.

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