Lightning protection by structure · Complies to IEC 62305-3 §5.3
Facade and Down-conductor Systems
Down conductors carry lightning current from the air termination to the earth termination by the shortest, straightest route. On facades they are fixed to the wall or hidden behind cladding, with a test joint near ground level on each one.
LPES solution codeFAC
Governing standardIEC 62305-3 §5.3
LPES design ruleSpacing 10 to 20 m; test joint at 1.5 m
When it applies
- Masonry and concrete buildings without continuous reinforcement to use
- Retrofits to existing buildings
- Curtain-wall and clad facades where the metal framing can be used or must be bonded
- Buildings where the conductor route must be hidden for appearance
When it does not
- Buildings whose steel frame or continuous rebar already serves as natural down conductors
- Routes close to doors and public areas without measures against touch voltage
- Facades with combustible cladding, unless the conductor is spaced off or the temperature rise is checked
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 |
|---|---|---|
| Protection level | LPL I–IV from the risk assessment; sets rolling-sphere radius 20 / 30 / 45 / 60 m | IEC 62305-2 · IEC 62305-3 |
| Number and spacing | At least two; spaced on average 10 / 10 / 15 / 20 m around the perimeter | IEC 62305-3 Table 5 |
| Route | Straight and vertical; no loops; bends kept gentle | IEC 62305-3 Cl. 5.3 |
| Conductor | Round 8 mm or tape 25 × 3 mm, minimum 50 mm² | IEC 62561-2 |
| Fixings | About every 1 m | IEC 62305-3 Annex D |
| Test joint | One on each down conductor, openable only with a tool | IEC 62305-3 Cl. 5.3.6 |
| Ring conductors | At ground level and at intervals up tall buildings to share the current | IEC 62305-3 Cl. 5.3 |
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 |
|---|---|---|
| LPS Conductors | Down conductors and interconnecting rings | Building height + roof and earth tails, per down conductor |
| Conductor Holders | Wall and facade holders | One per metre of down conductor |
| Test Joints & Inspection Housings | Test joint or inspection housing near ground level | One per down conductor |
| Earth Entry Rods & Lugs | Protected entry from the test joint into the ground | One per down conductor |
From design to handover
- Fix the number and position of down conductors from the protection level
- Choose exposed or concealed routes and check separation distances
- Fix holders, run the conductors and install test joints
- Connect to the earth termination through earth entry rods
- Measure continuity and earth resistance at each test joint and record
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 |
|---|---|---|
| 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. |
| CEA Safety Regulations 2023 | Reg 14(2), Reg 2(1)(zze) | Relevant standards, including the National Electrical Code and the National Building Code, shall be followed. Indian Standards come first, then IEC, IEEE and European Norms in that order. Where a standard and the regulations differ, the regulations prevail. |
| IS 3043:2026 | Clause 12.1.2.1, 13.7 | For lightning protection, a Type A earth electrode targets a resistance below 10 Ω, and the continuity of the lightning protection path is checked against 0.2 Ω. |
| IS 3043:2026 | Clause 11.1 | A buried earth grid is laid at least 500 mm deep, and the ring is bonded to the reinforcement every 5 m to 10 m, 5 m for buildings with information technology or telecom equipment. |
| CEA Safety Regulations 2023 | Reg 43(v) | Every building shall have protective equipotential bonding that interconnects exposed and extraneous conductive parts. |
| IEC 60364-6:2016 | Annex C | Earth electrode resistance is measured by fall-of-potential with auxiliary electrodes, by a loop impedance instrument, or by current clamps where auxiliary electrodes cannot be placed. |
| CEA Safety Regulations 2023 | Reg 32(2), Reg 33(3) | Periodic inspection or self-certification is set by the Appropriate Government at intervals not longer than five years. Test instruments are calibrated by a Government-authorised or NABL-accredited laboratory. |
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.
IEC 62305-3:2024 · LPES Knowledge Hub H-17
Down-conductor system current sharing number and spacing
The down-conductor system is the set of conductors that carries lightning current from the air-termination system to the earth-termination system. Its job is not just to exist but to share the current across several parallel paths, positioned close enough together and correctly enough to keep the voltage drop along any single path — and the separation distance it forces onto nearby metalwork and cabling — within safe limits. The standard sets a minimum number of down conductors, gives preferred spacing values by LPS Class in Table 5, and provides a current-partitioning coefficient (kc) that turns "how many, how far apart" into "how much current does each conductor actually carry."
How it is applied
- Start from the LPS Class already fixed for the structure (Clause 4) and the air-termination layout (5.2). Confirm the structure is attached (5.3.3) or isolated (5.3.2) — the minimum-number rule differs.
- For an attached LPS: apply the "not less than two" rule, place a conductor at every exposed corner where practicable, then fill the perimeter to the preferred spacing in Table 5 for the LPS Class in question.
- For an isolated LPS: apply 5.3.2's per-mast / per-support / per-wire-end minimum instead of Table 5's spacing directly (masts that are themselves metal or reinforced concrete need no separate down conductor).
- Route each conductor as the direct continuation of its air-termination conductor, straight and vertical; where a loop is unavoidable, check the loop's minimum internal distance against the separation distance s for that loop's conductor length (5.3.4, Figure 4).
- Decide whether any natural component (structural steel, continuous rebar, facade sub-structure) can be used instead of a dedicated conductor, and if so verify the specific conditions in 5.3.5 (continuity, dimensions, connection type) before relying on it.
- Fit a test joint (or test point, for embedded/natural components) at the base of every down conductor per 5.3.6.
- Where the separation distance to nearby metalwork, cabling or a door/window needs to be checked or minimised, select the matching Annex B figure for the actual air-termination/down-conductor configuration (wire, unringed multiple, ringed multiple, or meshed) and compute kc, then s, for the relevant points.
- Hand the finished down-conductor layout to the earth-termination design (5.4) so each conductor lands on an earth electrode consistent with the chosen Type A or Type B arrangement, and to the bonding/separation-distance design (6.2/6.3) so the current-sharing assumption behind kc is actually realised on site.
Common mistakes
- Installing only one down conductor on an attached structure — 5.3.3 requires not less than two, regardless of building size.
- Skipping exposed corners when placing conductors, even though 5.3.3 specifically calls them out as preferred locations.
- Treating the Table 5 value as a rigid grid rather than a preferred spacing to be adapted, within reason, to architectural and practical constraints (5.3.3) while still keeping the perimeter roughly evenly covered.
- Running a conductor through a gutter or downspout — explicitly prohibited in 5.3.4 regardless of insulation, because of the corrosion risk noted there.
- Accepting an unavoidable loop without checking its internal distance against the separation distance s for that loop's conductor length (5.3.4, Figure 4) — a loop that is "close enough" visually can still be electrically too tight.
- Assuming lightning current splits evenly across all down conductors (1/n each). Annex B shows the paths closer to the point of strike carry more current; using the naive average understates the separation distance actually needed there.
- Using structural steel or rebar as a natural down conductor without confirming electrical continuity by test, design record, or compliant connections — 5.3.5 makes this a precondition, not an assumption.
- Omitting test joints (or test points on natural/embedded components), which then makes it impossible to measure the earth-termination system in service (5.3.6).
- Confusing the down-conductor spacing of Table 5 (a positioning/number rule) with the separation distance s of 6.3/Annex B (a clearance rule to prevent sparking) — they use similar vocabulary but answer different questions and use different inputs.
Design checklist
- LPS Class confirmed (Clause 4) before sizing the down-conductor layout.
- Isolated or attached LPS identified — correct minimum-number rule applied (5.3.2 or 5.3.3).
- Not less than two down conductors on any attached structure.
- A down conductor placed at every exposed corner where practicable.
- Perimeter spacing checked against Table 5 for the applicable LPS Class.
- Each down conductor routed as a direct, straight, vertical continuation of its air-termination conductor wherever practicable.
- Any unavoidable loop checked: internal distance ≥ separation distance s for that loop's conductor length.
- No down conductor routed through a gutter or downspout.
- Wall-mounting method (surface, embedded, or offset) matched to the wall's combustibility classification, with the 100 mm² steel cross-section rule applied where the offset clearance cannot be assured.
- Any natural component (rebar, structural steel, facade sub-structure) checked against the specific continuity, dimension and connection conditions of 5.3.5 before being relied on.
- Test joint (or test point) provided at every down conductor's connection to the earth-termination system.
- Down-conductor layout matched to the chosen Type A or Type B earth-termination arrangement (5.4).
- Where separation distance is critical (near sensitive metalwork, cabling, doors/windows), the correct Annex B figure selected for the actual configuration and kc — not a flat 1/n assumption — carried into the s calculation.
IEC 62305-3:2024 · LPES Knowledge Hub H-18
Construction of down conductors routing loops and wall materials
A down conductor only does its job if it gives the lightning current the shortest, straightest, most direct route from the air-termination system to the earth-termination system; every metre it is forced to deviate from that route — a loop around a cornice, a detour into a gutter, a run pressed into flammable render — either raises the risk of a dangerous internal flashover or damages the building it is meant to protect. This section of IEC 62305-3:2024 turns that single idea into installable rules: how straight and vertical a run must be, what to do when a loop cannot be avoided, how far a conductor must sit from doors, windows and combustible walls, and what happens where a down conductor has to cross a cantilevered part of the structure.
How it is applied
- In practice this topic is applied as a route-and-check exercise carried out after the down-conductor count and spacing have already been fixed by 5.3.2/5.3.3.
- First, the designer sketches the shortest, straightest, most vertical route for each down conductor from its air-termination connection to its earth-termination connection, following the building's own corners and faces as directly as possible and treating a continuation of the air-termination conductor as the default.
- Second, every point where that route cannot stay straight — a projecting cornice, a re-entrant corner, an architectural feature — is checked as a loop: the loop's total conductor length is measured, the separation distance s is calculated from the LPS class and the insulation material between the loop's two ends, and the actual clearance across the loop is compared against s.
- If the clearance is short, the designer either re-routes the conductor to remove the loop, increases the physical clearance, or provides a direct bonding connection through the structure at the re-entrant point rather than accepting the loop.
- Third, every metre of the route is checked against the wall it will be fixed to: non-combustible walls allow surface or embedded fixing without restriction; normal-flammable walls allow surface fixing once the expected temperature rise has been shown not to be dangerous for that material; and easily-flammable walls require either a minimum 0.1 m standoff (with brackets permitted to touch the wall) or, where that standoff cannot be guaranteed, a heavier steel (or thermally equivalent) conductor of at least 100 mm² cross-section.
- Fourth, any section that will pass close to a cantilevered part of the structure where people can stand beneath it is checked against the d > 2.5 + s rule.
- Finally, the route is checked against the general prohibitions — never through a gutter or downpipe, kept clear of doors and windows by the separation distance where practicable — and fixing spacing, fastener type and (where relevant) test-joint location are specified so that the installed conductor can be inspected and measured later.
Common mistakes
- Treating "as straight and vertical as practicable" as a preference rather than a requirement, and accepting decorative or architecturally convenient loops without ever calculating the separation distance across them.
- Calculating the separation distance for a loop using only the straight-line span between the two ends of the loop, instead of the full conductor length l around the loop as the standard requires.
- Running a down conductor through a rain gutter or downpipe "because it is out of the way," missing both the explicit prohibition and the corrosion risk from trapped moisture.
- Fixing a down conductor flush against a timber-clad or other flammable facade without checking the material's classification under 5.2.4 or verifying that the expected temperature rise is not dangerous for that material.
- Assuming the 0.1 m clearance rule for easily-flammable walls also permits the mounting brackets themselves to be spaced off the wall, when the standard specifically allows the brackets to remain in contact with the wall while the conductor itself is held clear.
- Forgetting the 100 mm² minimum cross-section fallback for cases where the 0.1 m clearance from an easily-flammable material genuinely cannot be achieved, and instead leaving an undersized conductor too close to the wall.
- Ignoring cantilevered sections of a building in the separation-distance check, on the assumption that the down-conductor spacing rule (Table 5) alone is sufficient, when a person standing beneath a cantilever needs the specific d > 2.5 + s check from Annex D.
- Coating a down conductor in paint or PVC for appearance without confirming that the coating does not compromise the conductivity of its connections at joints and fixings.
- Treating the loop rule and the wall-material rule as unrelated checks, when in practice the tightest cases are often where both apply together — a looped conductor pressed against a combustible wall, where the lower km for masonry (0.5) roughly doubles the required separation distance compared with the same loop in open air.
Design checklist
- Has the route of every down conductor been drawn as straight and vertical as the building geometry allows, as a direct continuation of its air-termination conductor?
- Where a straight route is not possible, has every resulting loop been checked: is the actual clearance across the loop, including fixing components, at least equal to the calculated separation distance s?
- Has the separation distance for each loop been calculated using the full conductor length around the loop (l = l1 + l2 + l3, or as applicable), not the straight-line span?
- Has the correct ki (LPS class), km (insulation material at that point) and kc (current-sharing coefficient from Annex B) been used for each check?
- Has every down conductor been confirmed clear of gutters and downpipes along its whole length?
- Has the separation distance from doors and windows been checked where practicable?
- Has the wall material along each conductor's route been classified (non-combustible / normal-flammable / easily-flammable per 5.2.4), and has the corresponding fixing rule been applied?
- For easily-flammable walls: is the 0.1 m clearance achieved, or, where it cannot be, is the conductor steel (or thermal equivalent) of at least 100 mm² cross-section?
- Has every cantilevered section accessible to people been checked against d > 2.5 + s?
- Are fixings and fasteners specified to IEC 62561-4, spaced to resist wind, vibration, snow-slip and thermal-expansion loading, and consistent with the suggested Annex D spacing?
- Is a test joint (or test point, for embedded/natural down conductors) provided near the earth-termination connection of every down conductor?
- Where a natural component (facade element, structural steel, reinforced-concrete column) is used instead of a dedicated down conductor, has its electrical continuity and dimension been verified against 5.3.5 and Table 7?
- Has any decorative coating (paint, PVC) been confirmed not to impair conductivity at joints and connections?
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.
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
How many down conductors does a building need?
At least two, spaced around the perimeter at an average of 10 to 20 m depending on the protection level. Lightning Protection System Design
Can down conductors be hidden?
Yes — behind cladding, in plaster or in a duct — if the material is non-combustible and the test joint stays accessible. LPS Conductors
What is a test joint for?
It lets the down conductor be disconnected from the earth electrode so that each can be measured. Test Joints & Inspection Housings
How are people protected near a down conductor?
By insulating the conductor, by a high-resistivity surface layer, or by keeping people away. Step and Touch Voltage Control
What protects the conductor where it enters the ground?
An earth entry rod or a corrosion-protected section across the air-to-soil transition. Earth Entry Rods & Lugs
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.
