Earthing systems · Complies to IEEE 80-2013 · IS 3043 · CEA Reg. 43
Mat / Grid Earthing for Substations
Mat or grid earthing is a buried mesh of conductors under a substation, with rods at key points. It limits the earth potential rise during a fault and keeps step and touch voltages within tolerable limits.
When it applies
- Outdoor and indoor substations from 11 kV upward
- Switchyards, generating stations and large transformer yards
- Solar and wind pooling substations
- Industrial main receiving substations with high earth-fault currents
When it does not
- Low-voltage installations where rod or ring earthing meets the requirement
- Sites inside a proven global earthing system, where a reduced design may be justified by study
- Any site without soil resistivity data and a fault level — the grid cannot be sized without them
How the system works
- Read the soilSoil resistivity decides everything. A Wenner survey at several spacings shows whether to go deep, go wide or treat the soil.
- Choose the electrodeFoundation, ring, rod, plate or grid: each suits a different footprint, soil and fault duty.
- Make joints that lastBuried joints are welded or made with tested clamps, and protected wherever metals or soils change.
- Prove it and record itResistance and continuity are measured, labelled at the pit and filed in the handover record.
Why depth beats diameter
Current leaves an electrode through shells of soil. A longer rod reaches more soil and moister layers, so resistance falls quickly with depth. Figures are for one 17.2 mm rod in uniform 100 Ω·m soil.
Design parameters
The values a consultant or contractor needs to fix before the system is drawn.
| Parameter | Typical value or rule | Reference |
|---|---|---|
| Soil model | Two-layer model from a Wenner survey across the site | IEEE 80 · IEEE 81 |
| Fault duty | Maximum earth-fault current, current division factor and clearing time | IEEE 80 |
| Conductor size | From fault current, duration and material constants; usually copper or galvanised steel flat | IEEE 80 Cl. 11 |
| Grid geometry | Typical burial 0.5–0.6 m; mesh spacing about 3–7 m, closer at the corners | IEEE 80 |
| Tolerable voltages | Touch and step limits for a 50 kg or 70 kg body with the surface layer applied | IEEE 80 Cl. 8 |
| Surface layer | 100–150 mm crushed rock, about 3,000 Ω·m when wet | IEEE 80 |
Solution pack: component BOQ
Each line opens the LPES product category. Part codes and final quantities are confirmed on your quote from the drawings.
| Component | Role in the system | Quantity rule |
|---|---|---|
| Earth Mats & Grids | Grid conductor and prefabricated mats, including operator mats at switch handles | Total grid length from the design + 5% for joints and risers |
| Substation & Switchyard Earthing | Risers, structure and fence earthing, equipment clamps | Two risers per major equipment; fence earthed at corners and gates |
| Exothermic Welding | Permanent joints at every crossing and riser | One weld per grid crossing, tee and rod |
| Earth Rods | Deep electrodes at the perimeter, transformer neutrals and surge arresters | From the design; typically at grid corners and each neutral and arrester |
From design to handover
- Survey soil resistivity and build the soil model
- Design the grid for the fault duty and check touch, step and transferred voltages
- Trench, lay and weld the grid, and drive the rods
- Connect every item of equipment with two risers and earth the fence
- Measure grid resistance, and step and touch voltages where required, then spread the surface layer
Services for this solution
Earthing System DesignStep & Touch Voltage MeasurementGrid Resistance / Substation Earthing Test
Industries that use it
What the standards require
Checked against the current editions held in the LPES standards library.
- IS 3043:2026 Cl. 6.3
- Independent, 'dedicated' or unbonded 'clean' electrodes are listed as misconceptions that shall not be followed. The code recommends one interconnected, meshed earthing and bonding network.
- IS 3043:2026
- Quick estimates: a rod gives R ≈ ρ ÷ L, a strip or ring R ≈ 2ρ ÷ L and a plate R ≈ 0.8ρ ÷ perimeter, with rods at least one length apart.
- IEC 62305-3:2024 Cl. 5.4
- Type A electrodes start at least 0.5 m below ground, and 0.5 m is added to a vertical rod for the dry or frozen top layer.
- IEC 62305-3:2024 Cl. 5.4
- A ring touching soil for less than 80% of its length counts as Type A. Neighbouring electrode resistances should agree within a factor of two.
- IS 3043:2026 cl. 8.1.7
- Earth enhancing compound only where soil resistivity is above 3,000 Ω·m, never below 200 Ω·m, and in India only for lightning protection earthing, to IS 18925 (Part 7).
- IS 3043:2026
- Where soil pH is below 6 or above 10, change the backfill or encase the electrode in concrete.
Regulation and standards cross-check
What Indian regulation and the wider standards add to this solution. Paraphrased; confirm against the current official text, amendments and state notifications before relying on a clause in a tender or inspection.
| Standard | Clause | What it requires |
|---|---|---|
| CEA Safety Regulations 2023 | Reg 50 | Above 650 V the whole switchyard or substation, including non-current-carrying metal, is connected to an earthing system or mat that limits touch and step potential and earth potential rise, including potential transferred through earth wires, cable sheaths, fences and pipelines. |
| IS 3043:2026 | Clause 10.3, Figure 63, Table 28 | Substation earthing above 1 kV follows a step-by-step flow. A global earthing system is confirmed when the earth potential rise is below the permissible touch voltage. Table 28 limits for interconnection and transferred potential are checked as well. |
| IEC 61936-1:2021 | 10.2.1, Annex B, Annex C | The safety criterion is the permissible touch voltage against fault duration, about 650 V at 100 ms falling to about 120 V at 1 s. Meeting the touch-voltage limit generally satisfies step voltage. The IEEE 80 curve is an allowed alternative. |
| IEC 61936-1:2021 | 10.2.2 | The earthing system carries fault current within thermal and mechanical limits based on back-up protection operating time, keeps its integrity for the installation lifetime allowing for corrosion, and limits potential rise, potential differences and transferred potentials. |
| IEC 61936-1:2021 | 10.2.3, Table 6 | High-voltage and low-voltage earthing are interconnected where practicable. Where low-voltage circuits leave the high-voltage earthing area, earth potential rise is held to 1,200 V for faults cleared within 5 s and 250 V beyond 5 s, unless a global earthing system exists. |
| IEEE Std 80-2013 | Clause 8.4, Eq. 29 to 33 | Tolerable touch voltage is (1000 + 1.5 Cs ρs) × k ÷ √ts and tolerable step voltage is (1000 + 6 Cs ρs) × k ÷ √ts, with k = 0.116 for a 50 kg person and 0.157 for 70 kg, valid for 0.03 s to 3 s. The 50 kg value applies where the public can have access. |
| IEEE Std 80-2013 | Clause 16.4, Figure 32 | Grid design runs through twelve steps: field data, conductor size, tolerable voltages, initial layout, grid resistance, grid current, ground potential rise, mesh and step voltage, the two voltage checks, revision, and detail design. A ground potential rise above the touch limit is not a failure by itself. |
| IEEE Std 80-2013 | Clause 11, Clause 15 | Two currents are kept separate. The conductor is sized for the maximum future fault current at any bus with no split factor. The grid current uses only the share that flows to remote earth, with the split factor, the decrement factor and an allowance for growth. |
| IEEE Std 80-2013 | Clause 16.5, 16.8 | The simplified mesh and step equations hold for uniform soil, uniform spacing, 1 to 40 meshes per side and mesh sizes of 2.5 m to 22.5 m. Two-layer soil, unequal spacing and large or complex sites need computer analysis. |
| IEEE Std 80-2013 | Clause 19 | The built grid is verified in the field by fall-of-potential measurement, touch and step voltage surveys and grid integrity tests. The 61.8% probe rule holds only for uniform soil and long traverses. |
IEEE 80 Annex B benchmark: a 70 m × 70 m grid in 400 Ω·m soil, buried 0.5 m at 7 m spacing with 1,908 A grid current, gives a mesh voltage of about 1,002 V against a tolerable 838 V for a 70 kg person at 0.5 s. The design fails. Adding twenty 7.5 m perimeter rods brings the mesh voltage to about 747 V, and it passes. Low grid resistance alone would not have shown this.
What we ask for before design starts
- Single-line diagram showing every source and operating mode: transformer, generator, UPS, solar
- System earthing type at each level: TN-S, TN-C-S, TT or IT
- Earth-fault current and the normal and back-up clearing times
- Soil resistivity survey with the season it was taken in
- Site layout with foundations, buried metal, fences and services
- For high voltage: current division, surface layer and whether the public has access
Engineering depth: from the LPES Knowledge Hub
Topic studies written against the current standards. Open each part for the method, the mistakes to avoid and the checklist.
IEEE Std 80-2013 · LPES Knowledge Hub H-53
The twelve-step ground grid design procedure and its block diagram
Clause 16.4 of IEEE Std 80-2013 lays out, as twelve numbered steps, the complete sequence a designer follows to turn site data into an approved ground grid: gather field data, size the conductor, set the tolerable voltage limits, sketch a preliminary layout, estimate its resistance and current, check whether the preliminary design is already safe, calculate the actual mesh and step voltages if not, compare both against the tolerable limits, loop back to revise the design if either fails, and finally add the detail work — equipment pigtails, arrester rods, and a check for transferred-potential and special-area hazards — once the core design passes. Figure 32 renders this same sequence as a block diagram with two decision diamonds (Step 7's early-exit check and Steps 9-10's pass/fail checks) and one feedback loop back to "Modify design" (Step 11), so the whole procedure can be followed as a flowchart as easily as read as prose.
How it is applied
- Use 16.4 as the master checklist for any new substation grounding design: work the twelve steps in the stated order, and do not skip Step 7's early-exit test even when a full computer analysis is planned, since a GPR already below Etouch means the design effort at Steps 8-11 can be redirected to the Step 12 detail work instead.Use Figure 32's two feedback arrows out of Step 11 as a reminder that a revised design is not re-checked only against mesh/step voltage: because changing spacing or adding rods changes the grid's resistance as well, the revision loop in the diagram explicitly re-enters Step 5 (Grid resistance) as well as Step 8 (Mesh & step voltages), not Step 8 alone.Use the Step 12 closing instruction — reviewing for transferred-potential and special-area hazards per Clause 17 — as a hard gate before calling a design complete: a design that passes Steps 9 and 10 but has not been checked against Clause 17's fence, switch-shaft, rail, pipeline and cable-sheath hazards is not yet a finished design under this procedure.Use the procedure's own step numbers as the organising structure for a project's calculation package or design report, so a reviewer can trace each deliverable (soil report, conductor sizing calc, tolerable-voltage calc, preliminary layout, resistance estimate, grid-current calc, Em/Es calc, revision log if any, detail-design drawings) directly against the clause that produced it.
Common mistakes
- Skipping the Step 7 early-exit test and running the full Step 8 mesh/step calculation regardless — harmless but wasteful; the standard specifically provides Step 7 to avoid unnecessary work when GPR is already safe.
- Treating a Step 11 revision as a patch applied only to the voltage check, without re-running Step 5's resistance estimate — Figure 32's diagram explicitly routes the revision loop back into both Step 5 and Step 8, because added rods or tighter spacing change grid resistance too.
- Declaring the design complete once Step 9 and Step 10 pass, without carrying out Step 12's mandatory review of transferred-potential and special-area hazards under Clause 17 — the procedure's last sentence makes this review part of Step 12, not an optional add-on.
- Using the shortest fault-clearing time found anywhere in the protection scheme for tc at Step 2, rather than the maximum possible clearing time including backup protection, as Step 2 specifically requires.
- Reading the twelve steps as independent checklist items that can be done in any order or in parallel — the procedure is sequential by design, with each step's output feeding the next, and the revision loop exists precisely because an out-of-order approach breaks that dependency chain.
Design checklist
- Steps 1-3 (field data, conductor size, tolerable voltage criteria) completed and documented before any layout is drawn.
- Preliminary design (Step 4) sketched with a full perimeter loop and adequate cross-conductors.
- Resistance (Step 5) and grid current (Step 6) estimated for the preliminary design.
- Step 7 early-exit test (IG × Rg < Etouch) checked explicitly before proceeding to mesh/step calculation.
- If Step 7 fails: Em and Es calculated (Step 8) and checked against Etouch and Estep (Steps 9-10).
- Any failed check routed through Step 11's revision loop, with Step 5 and Step 8 both re-run on the revised design, not Step 8 alone.
- Step 12's detail design completed, including equipment pigtails, arrester/neutral rods, and the mandatory review for transferred-potential and special-area hazards under Clause 17.
Try the numbers
Earth rod resistance estimator
- One rod
- –
- All rods in parallel
- –
- Minimum rod spacing
- –
R = ρ ÷ (2πL) × [ln(8L ÷ d) − 1], uniform soil, rods spaced at least one length apart. An estimate for planning; the design uses your measured soil model.
Tolerable touch and step voltage
- Tolerable touch voltage
- –
- Tolerable step voltage
- –
- Surface derating Cs
- –
IEEE Std 80-2013, equations 27 and 29 to 33. Set the thickness to 0 for no crushed-rock layer. These are limits; the grid design must keep mesh and step voltage below them.
What we find on audits
- Electrodes spaced closer than their own length, so extra rods add little
- Salt and charcoal backfill that corrodes the electrode within a few years
- Copper joined directly to galvanised steel in soil
- Separate earths for lightning, power and electronics left unbonded
- No test link, so the electrode cannot be measured without cutting a conductor
What you receive: the LPES Protection Passport
- As-built drawings of the installed system
- Risk assessment and design calculations
- Test results: earth resistance, continuity, SPD checks
- Component list with part codes and type-test references
- Inspection schedule for the protection level
Lightning to Load: one accountable partner
- Assess
- Design
- Specify
- Supply
- Implement
- Verify
- Assure
Standards basis
IS 3043:2026 · IEC 62305-3:2024 (Ed. 3) · IEC 60364-5-54 · IEEE 80-2013 · CEA Safety Regulations 2023 · IEC 62561 series · IS 732:2019 · IEC 60364-6:2016 · IEC 61936-1:2021
Reviewed by LPES engineering, November 2026. Clause and table numbers follow IEC 62305:2024 (Edition 3) and IS 3043:2026.
Questions engineers ask
What earth resistance should a substation grid have?
IEEE 80 designs for safe touch and step voltages, not a fixed resistance. Values below 1 Ω are common for large substations and up to about 5 Ω for small ones. Grid Resistance / Substation Earthing Test
Copper or galvanised steel for the grid?
Copper resists corrosion and carries more current for its size. Galvanised steel flat is widely used in India with a corrosion allowance; the design covers either. Earth Mats & Grids
Why is crushed rock spread over the yard?
The high-resistivity layer raises the tolerable touch and step voltage by limiting current through the body. Step & Touch Voltage Measurement
How are grid joints made?
By exothermic welding, which gives a joint that carries the same fault current as the conductor and does not loosen. Exothermic Welding
How do I earth the fence?
Either bond it to the grid, with the grid extended beyond the fence line, or isolate and earth it separately; the study decides which. Substation & Switchyard Earthing
Get this solution quoted for your site
Send the drawings or the basic dimensions. LPES returns the design parameters, the BOQ with part codes and the price in one offer.
