Lightning protection by structure · Complies to IEC 62305-3 §8
Step and Touch Voltage Control
When lightning current flows to earth, the voltage on a down conductor and across the ground near it can injure people standing close by. Step and touch voltage control reduces that risk with insulation, a high-resistivity surface layer, potential grading and restricted access.
When it applies
- Down conductors beside entrances, walkways and places where people gather
- Stadiums, resorts, temples, schools and open public areas
- Substation and tower surroundings
- Shelters and lone structures where people wait during storms
When it does not
- Areas with a very low chance of people within 3 m of the down conductors
- Buildings with ten or more natural down conductors, such as a steel frame or continuous reinforcement
- Ground already covered with an insulating layer such as 5 cm of asphalt
How the system works
- InterceptAir termination is placed by rolling sphere, mesh or protective angle so that the strike lands on the system, not the structure.
- ConductSeveral straight, short down conductors share the current and keep voltages low.
- DisperseThe earth termination spreads the current into the ground with a low impulse impedance.
- EqualiseBonding and surge protection stop sparks between the system and what is inside the building.
Rolling sphere method
A sphere of the radius set by the protection level is rolled over the structure. Wherever it touches, a strike can land, so that point needs air termination. Everything it cannot touch is protected.
Design parameters
The values a consultant or contractor needs to fix before the system is drawn.
| Parameter | Typical value or rule | Reference |
|---|---|---|
| Zone of concern | Within 3 m of a down conductor | IEC 62305-3 Cl. 8 |
| Insulation of the down conductor | 100 kV, 1.2/50 µs impulse withstand — for example 3 mm cross-linked polyethylene | IEC 62305-3 Cl. 8.1 |
| Surface layer | Contact resistance of 100 kΩ or more within 3 m, for example about 5 cm of asphalt | IEC 62305-3 Cl. 8 |
| Potential grading | Meshed earth electrode or grading rings around the down conductor | IEC 62305-3 Cl. 8.2 |
| Access control | Barriers and warning notices | IEC 62305-3 Cl. 8 |
| Verification | Measured step and touch voltages where required | IEEE 81 |
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 |
|---|---|---|
| Step Touch Conductor® — Insulated Conductors | Insulated down conductor over the lowest 3 m and where people can touch it | 3 m per exposed down conductor, or the full run |
| Earth Mats & Grids | Potential grading mat or mesh under standing areas | Standing area within 3 m of each down conductor |
| Signs, Labels & Identification Plates | Warning notices at down conductors and earth pits | One per accessible down conductor |
From design to handover
- Identify every down conductor within reach of people
- Choose the measure: insulation, surface layer, grading or restriction
- Install insulated conductor and grading mats
- Fit warning notices and barriers
- Measure and record step and touch voltages where the study requires it
Services for this solution
Industries that use it
What the standards require
Checked against the current editions held in the LPES standards library.
- IEC 62305-3:2024 Cl. 5.2
- The rolling sphere is the general method. The protection angle only supplements it for simple shapes, and the mesh method is for flat surfaces.
- IEC 62305-3:2024 Cl. 5.2
- An unprotected metal roof fixture needs its own protection if it stands more than 0.3 m above the roof, covers more than 1.0 m² or is longer than 2.0 m.
- IEC 62305-3:2024 Cl. 5.2.3
- Side flashes are negligible up to 60 m. Above that, protect the top 20% of the height.
- IEC 62305-3:2024 Cl. 5.3
- An exposed corner can share a down conductor if both neighbours are within half the Table 5 spacing.
- IEC 62305-3:2024 Cl. 5.3.5
- Natural down conductors are proven by a four-lead continuity test at about 10 A: 0.2 Ω or less from top to earth network.
- IEC 62305-3:2024 D.7.2
- Inspect visually every year and completely, with electrical tests, every three years; every year for public, sensitive and explosion-risk structures.
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 |
|---|---|---|
| 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 17 | Special areas are checked one by one: the fence, with a perimeter conductor about 1 m outside it or bonding, operating-handle mats, cable sheaths, surge arrester earthing, and potentials transferred by communication circuits, pipes, rails and low-voltage neutrals. |
| 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. |
| 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. |
| 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. |
| CEA Safety Regulations 2023 | Reg 38(3)(vi) | Lightning protection is required for multi-storeyed buildings above 15 m and for listed premises, which include hospitals, hotels, academic buildings, industrial installations and other public buildings. The regulation names no design standard, so IS/IEC 62305 applies through Reg 14. |
What we ask for before design starts
- Roof plan, elevations and sections with heights
- Use of the structure and its contents, for the risk assessment
- Roof and facade materials with sheet thickness
- Metal installations on the roof and services that enter the structure
- Soil resistivity and the existing earthing layout
- Single-line diagram for the surge protection design
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-14
Step, touch and metal-to-metal touch voltage limits Estep Etouch and Emm for 50kg and 70kg, and sustained ground currents
Once the shock situations of a substation have been identified — step, touch, mesh, transferred, and metal-to-metal, whether in an air-insulated yard (Clause 8.2) or a gas-insulated one (Clause 8.3) — a grounding design needs a numeric ceiling for each one: the maximum driving voltage a person's body may be exposed to without the current through it reaching the fibrillation threshold within the fault-clearing time. IEEE Std 80-2013 Clause 8.4 supplies that ceiling in closed form. Starting from the general circuit relations Estep = (RB + 2Rf)·IB and Etouch = (RB + Rf/2)·IB, and substituting the body-current duration formula IB = k/√ts from Clause 6 together with the foot-resistance term Rf = (ρs/4b)·Cs from Clause 7, the clause produces four ready-to-use equations — Estep50, Estep70, Etouch50 and Etouch70 — each a function only of the surface-material derating factor Cs, the surface resistivity ρs, and the shock duration ts. A further substitution, setting the surface term to zero because a metal-to-metal contact has no foot-to-soil resistance in the circuit, gives the simplest pair in the whole clause, Emm-touch50 = 116/√ts and Emm-touch70 = 157/√ts. Clause 8.5 then adds a single qualitative caution: even after these limits are met, sustained low-level fault currents below the protective-relay setting but above the let-go threshold can still cause asphyxiation from prolonged muscle contraction, and the standard explicitly does not expect a design to also guard against merely painful, non-injurious shocks.
How it is applied
- The clause is applied as a direct substitution exercise once four inputs are fixed by the designer or by site data: (1) the body-weight criterion (50 kg, the default for publicly accessible areas, or 70 kg, usable "inside fenced switchyards not accessible to the public" per the Clause 6.2 condition); (2) the surface-layer derating factor Cs and resistivity ρs, from Clause 7.4 (Figure 11 or Equation 27), or Cs = 1 / ρs = ρ if no surface layer exists; (3) the shock duration ts, chosen as the fault-clearing time per Clause 5.3/6.2; and (4) which of step, touch or metal-to-metal applies, based on the shock situation identified under Clause 8.2 (air-insulated) or 8.3 (GIS).
Common mistakes
- Mixing the 50 kg and 70 kg constants within the same calculation (e.g. using k=0.157 in an equation intended for the 50 kg criterion), or applying the 70 kg criterion to a publicly accessible area without confirming the population-weight condition that justifies it.
- Forgetting that "If no protective surface layer is used, then Cs = 1 and ρs = ρ" (8.4's own text) — using ρs = 0 or omitting the term entirely when there is genuinely no surface layer, rather than substituting the native soil resistivity.
- Applying the general touch-voltage equation (32)/(33), with its Cs·ρs surface term, to a metal-to-metal contact case instead of the metal-to-metal-specific Equations (34)/(35) — 8.4 is explicit that metal-to-metal contact removes the surface/foot-resistance term entirely because "the total resistance of the accidental circuit is equal to the body resistance, RB."
- Treating ts as an arbitrary design choice rather than the actual fault-clearing time — a ts chosen too generously inflates the tolerable-voltage limit beyond what the actual protection scheme can deliver.
- Reading Clause 8.5 as if it supplied a further voltage limit to calculate. It does not: it is a qualitative reminder about sustained sub-relay-setting currents, not an Equation-(36)-style formula.
Design checklist
- Confirm the body-weight criterion (50 kg or 70 kg) matches the actual accessibility of the area being assessed.
- Confirm Cs and ρs are taken correctly: from Figure 11/Equation (27) where a surface layer exists, or Cs = 1 / ρs = ρ where it does not.
- Confirm ts is the actual primary or backup fault-clearing time applicable to the location and fault type being assessed, not an arbitrary assumption.
- Use Equations (29)/(30) for step voltage, (32)/(33) for touch voltage, and (34)/(35) — not (32)/(33) with ρs forced to zero by hand — for metal-to-metal touch voltage.
- Compare the calculated actual step, touch or metal-to-metal voltage against the corresponding limit from this clause per the 8.4 comparison rule, and treat a fail as requiring a design revision (Clause 16.6), not a documentation workaround.
- Separately from the voltage-limit comparison, confirm Clause 8.5's sustained-low-level-current consideration has been reviewed for any protection scheme where relay pickup settings could allow a sub-threshold fault current to persist.
Try the numbers
Protection level explorer
- Rolling-sphere radius
- 45 m
- Mesh size
- 15 × 15 m
- Down-conductor spacing
- 15 m
- Peak current covered
- 100 kA
- Coefficient ki
- 0.04
- Interception efficiency
- 90%
Values from IEC 62305-1 and IEC 62305-3. The level for your structure comes from the risk assessment.
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
- Rooftop equipment standing outside the protected volume
- A single down conductor, or long loops around parapets
- Separation distance ignored, so current jumps to ducts and cable trays
- No test joints and no record of earth resistance
- External lightning protection installed with no surge protection on incoming lines
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
IEC 62305-1, -2 and -3:2024 (Ed. 3) · IS/IEC 62305 · IEC 62561 series · CEA Safety Regulations 2023 · 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 is the difference between step and touch voltage?
Touch voltage is between a hand on the conductor and the feet. Step voltage is between two feet on the ground near where current enters the earth. Step & Touch Voltage Measurement
How is a down conductor insulated?
With a conductor whose insulation withstands a 100 kV impulse, used over at least the lowest 3 m. Step Touch Conductor® — Insulated Conductors
Does gravel or asphalt help?
Yes. A low-conductivity surface layer, such as about 5 cm of asphalt, raises contact resistance and reduces the current through a person. Earth Mats & Grids
Are warning signs enough?
Signs and barriers are accepted measures, but they rely on behaviour. Insulation and grading protect without it. Signs, Labels & Identification Plates
Is this the same as substation step and touch design?
The principle is the same; substations are designed for power-frequency faults under IEEE 80. Mat / Grid Earthing for Substations
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.
