Systems and special applications · Complies to IEC 62305-4 · IEC 61643-12
Surge Protection by Lightning Protection Zone
The lightning protection zone concept divides a building into zones of decreasing lightning threat, from LPZ 0 outside to LPZ 3 inside equipment. A surge protective device is fitted wherever a line crosses a zone boundary, and the devices are coordinated so that each one handles its share.
When it applies
- Buildings with an external lightning protection system
- Facilities with electronics whose failure is costly
- New installations, where zones can be planned with the cable routes
- Existing sites with repeated surge damage
When it does not
- Protection of a single appliance in isolation — one plug-in device is not a zone concept
- The external LPS, which is designed from the structure solutions
- Systems whose voltage, earthing arrangement or fault level is unknown
How the system works
- DefineZones, bonding points and what must be evidenced are fixed on the drawings first.
- SelectEach component is chosen by its rating and the standard it is tested to.
- InstallConnections are kept short and every joint is made with a tested component.
- VerifyThe system is measured, labelled and recorded before handover.
Coordinated surge protection
Each device takes its share. The Class I device diverts lightning current at the service entry; Class II and III devices bring the remaining voltage below what the equipment can withstand.
Design parameters
The values a consultant or contractor needs to fix before the system is drawn.
| Parameter | Typical value or rule | Reference |
|---|---|---|
| LPZ 0 to LPZ 1 | Type 1 SPD tested with 10/350 µs lightning current at the service entry; at least 12.5 kA per pole | IEC 62305-4 · IEC 60364-5-534 |
| LPZ 1 to LPZ 2 | Type 2 SPD tested with 8/20 µs at sub-distribution boards | IEC 61643-11 |
| LPZ 2 to LPZ 3 | Type 3 SPD at or near the equipment | IEC 61643-11 |
| Voltage protection level | Up below the impulse withstand of the equipment: 6 / 4 / 2.5 / 1.5 kV for categories IV to I on 230/400 V | IEC 60664-1 |
| Connecting leads | Total length 0.5 m or less | IEC 60364-5-534 |
| Protective distance | Additional SPD when the cable from SPD to equipment exceeds about 10 m | IEC 60364-5-534 |
| Data lines | SPD at each boundary, matched to the signal | IEC 61643-21 · IEC 61643-22 |
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 |
|---|---|---|
| Type 1 Lightning-current Arresters | Lightning current arrester at the service entry | One set per incomer, by earthing arrangement |
| Type 2 SPDs | Surge arrester at sub-distribution boards | One set per board |
| Type 3 SPDs (DIN rail) | Fine protection at the equipment | One per sensitive load or socket group |
| Data, Signal & RF Line SPDs | Protection of data, signal and communication lines | One per line per boundary |
| SPD Panels & Surge Boxes | Pre-wired SPD panels where the board has no space | One per board without a spare way |
From design to handover
- Define the zones on the building layout
- List every power and data line that crosses a boundary
- Select and coordinate the SPDs from system data and protection level
- Install with short leads and the correct backup protection
- Verify, label and record the SPD schedule
Services for this solution
Industries that use it
What the standards require
Checked against the current editions held in the LPES standards library.
- IEC 62305-4:2024
- A coordinated SPD system protects against conducted surges only. Radiated fields need shielding and cable routing.
- IEC 62305-4:2024 Cl. 7
- Where an external LPS exists, a Class I (Type 1) SPD is required at the service entry.
- IEC 62305-4:2024
- Earthing conductor to the SPD: 16 mm² copper for Class I, 6 mm² for Class II and 1.5 mm² for Class III.
- IEC 62305-3:2024 Tables 9 and 10
- Bonding conductors: 16 mm² copper between bonding bars or to earth; 6 mm² copper from internal metal installations to a bar.
- IS 3043:2026 Cl. 6.3
- One interconnected, meshed earthing and bonding network, with all electrodes, the main earthing terminal and the LPS integrated.
- IEC 62305-3:2024 D.7.2
- Inspect visually every year and completely every three years; every year for sensitive systems 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 |
|---|---|---|
| IS 732:2019 | Clause 1, 4.5.3, 5.3.5 | The wiring code covers installations up to 1,000 V a.c. or 1,500 V d.c. Its surge clauses govern whether a surge protective device is needed and how it is selected, connected and coordinated. |
| CEA Safety Regulations 2023 | Reg 121, 77, 124(7) | The regulations name surge and lightning protection for solar plants, lines and substations, and EV charging stations. They set no general surge protective device mandate for every building, so the IEC 62305-2 risk assessment decides. |
| CEA Safety Regulations 2023 | Reg 77 | Owners of overhead lines, substations and generating stations exposed to lightning must divert lightning surges to earth. The arrester earthing lead is kept as short and straight as possible, does not pass through steel pipe, and goes to a separate vertical electrode or to a junction of the earth mat. |
| CEA Safety Regulations 2023 | Reg 121 | Solar plants need lightning and overvoltage protection with lightning arresters, a surge protective device with arc-extinguishing capability in every combiner box, earth-fault protection with insulation monitoring, and earthing of all array structures, frames and enclosures with welded strip connections. |
| IS 3043:2026 | Clause 11.8 | Data centres use TN-S with a meshed bonding network. Where a high-voltage substation shares the earthing network, fault clearing below 0.1 s is called for. |
| IEC 60364-6:2016 | 6.4.3.3 | Surge protective devices are disconnected for the insulation resistance test. Where that is impracticable the test voltage may be reduced to 250 V d.c., and the result must still be at least 1 MΩ. |
| 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. |
What we ask for before design starts
- Single-line diagram with sources, operating modes and earthing arrangement
- Equipment list with impulse withstand levels
- Cable routes and every point where services enter
- Fault levels and protection clearing times
- Existing earthing and lightning protection records
- Site layout with fences, pipes, rails and neighbouring installations
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 62305-4:2024 · LPES Knowledge Hub H-48
Where to put SPDs according to the source of damage S1–S4 (Figure C.1)
A coordinated SPD system only works if each SPD is put where the surge it has tohandle actually enters the installation. IEC 62305-4:2024 Annex C sorts everysurge entry into four sources of damage - S1 (a flash to the structure itself),S2 (a flash near the structure), S3 (a flash to a service, i.e. a line, connectedto the structure) and S4 (a flash near a service) - and Figure C.1 shows, for asingle generic structure with a power line and a telecom/signal line entering it,exactly which SPD positions are needed to cover which of those four sources. Getthe source of damage wrong and you either leave a real entry point unprotected oryou install and pay for an SPD that is doing nothing.
How it is applied
- Step 1: from the structure's risk assessment (IEC 62305-2:2024), identify which of S1, S2, S3, S4 are relevant to the structure and cannot be neglected.
- Step 2: decide which Figure C.1 view applies. If the structure has no external LPS and the only surge entry paths under consideration are the incoming lines, use Figure C.1 a) (S3 and S4 only). If the structure has (or requires) an external LPS, or a roof-mounted installation such as an antenna is present, or S1/S2 cannot be neglected, use Figure C.1 b) (all four sources).
- Step 3: place an SPD "at origin of installation" on every service (power line, telecommunication/signal line) entering the structure, as required by IEC 60364-4-44, to intercept S3/S4-type surges arriving on that line.
- Step 4: where oscillation or induction effects mean the origin-of-installation SPD alone will not adequately protect the equipment, add a second SPD "close to equipment" (this decision is finalised using C.2.2, once the current rating is set).
- Step 5: where a roof-mounted installation (e.g. an antenna) is present and separation distance from the LPS cannot be maintained, or inductive coupling with that roof installation is possible, add the dedicated SPD called for in the unnumbered key item of Figure C.1 to protect the equipment fed from that installation.
- Step 6: carry the chosen SPD locations forward into C.2.2 (current rating) and C.2.3 (voltage protection level) to complete the SPD's specification.
Common mistakes
- Treating "install an SPD at the service entrance" as sufficient in every case, without checking whether S1/S2 (structure-borne) or a roof-mounted installation make Figure C.1 b)'s extra SPD positions necessary.
- Forgetting the SPD driven purely by a roof-mounted installation (e.g. an antenna) when separation distance to the LPS cannot be kept - this is a distinct SPD location from the ordinary origin-of-installation and close-to-equipment positions.
- Confusing "near the structure" (S2) and "near a service" (S4) - they drive different SPD locations (S2 relates to the structure's own exposure, S4 to a connected line's exposure) even though both describe a nearby, not direct, flash.
- Choosing SPD locations before the risk assessment has actually confirmed which of S1-S4 are relevant - Clause C.2.1 is a consequence of the risk assessment, not a substitute for it.
Design checklist
- Risk assessment has identified which of S1, S2, S3, S4 are relevant for this structure and cannot be neglected.
- Correct Figure C.1 view selected (a: S3/S4 only vs b: all four sources), based on presence of an external LPS and/or roof-mounted installations.
- An SPD "at origin of installation" is placed on every power and telecommunication/signal line entering the structure.
- Need for a "close to equipment" SPD assessed against oscillation/induction effects (to be finalised in C.2.2).
- Roof-mounted installations (antennas, etc.) checked for separation distance to the LPS and inductive coupling; dedicated SPD added if either cannot be met.
- SPD locations fixed here are carried forward, unchanged, into C.2.2 (current rating) and C.2.3 (voltage protection level).
IEC 62305-4:2024 · LPES Knowledge Hub H-49
Selecting SPDs by lightning current test class I II III and telecom classes D1 C2, when class I is mandatory
Once you know where an SPD has to sit in a structure's electrical system, the next decision is which discharge capability that SPD needs to have — in plain terms, how much lightning current it must survive without failing. Getting this choice wrong in either direction is expensive: an under-classed SPD tested only to class II sitting where partial lightning current actually flows will fail catastrophically on the first real strike; an over-classed class I SPD installed everywhere "to be safe" adds unnecessary cost and, in some circuit positions, unnecessary follow-current and coordination complexity. The clause gives the rule for making that call correctly, and points to IEC 62305-2:2024 Annex B for the numeric current values that then size the SPD.
How it is applied
- In practice, an engineer working through Annex C classification for a given SPD position runs through this sequence: (1) confirm, from C.2.1 / Figure C.1, which source(s) of damage (S1-S4) that SPD position is exposed to; (2) check whether the structure carries an external LPS, or whether direct-lightning protection is otherwise specified for it — if yes, class I / D1 is required at the entrance SPD without further debate; (3) if there is no external LPS, check whether a direct or partial strike to the incoming overhead line between the last pole and the service entrance is a credible event for that specific site — if yes, class I / D1 may still be needed at or near the origin of the installation; (4) for any SPD not caught by rules (2) or (3), and for any secondary equipment-proximate SPD flagged by Figure C.1 items 2 or 4, apply class II / C2 by default, and only escalate to class I / D1 if the specific oscillation/induction or source-of-damage condition at that position calls for it; (5) where the classification is borderline on S1/S3 exposure alone, check the NOTE 1 frequency condition (ND + NL + NDJ ≤ 0,01/year) against the site's own IEC 62305-2 risk assessment before finalising the lighter class; (6) once class I or class II is settled for each SPD position, take the classification into IEC 62305-2:2024 Annex B, together with the structure's required LPL and the specific source of damage, to read off the actual numeric Iimp or In value the SPD must be rated to.
- This clause's decision therefore feeds directly into procurement and specification documents: it is what an engineer points to when a datasheet is checked for "Class I, tested to IEC 61643-11" versus "Class II, tested to IEC 61643-11" (or the D1/C2 telecom equivalents), and it is the clause that should be cited on a design basis or SLD annotation whenever an SPD's test class is specified.
Common mistakes
- Specifying class II everywhere on a structure that has an external LPS, on the assumption that "the SPD just needs to handle surges" without checking whether the specific position sits in a genuine lightning-current path — C.2.2's should/shall wording makes class I mandatory, not optional, once the structure is LPS-protected.
- Treating class I and class D1 (or class II and class C2) as separate, unrelated classification schemes rather than recognising they are the same underlying discharge-capability tier expressed for two different product/circuit types (power versus telecommunication/signal).
- Reading NOTE 1's 0,01-per-year frequency condition as a blanket exemption from class I anywhere on a low-risk site, when it only addresses the S1/S3-based justification for class I — it does not override the separate, unconditional LPS-presence rule.
- Confusing Iimp (class I test parameter, associated with charge transfer Q and specific energy W/R) with In (class II test parameter, an 8/20 waveshape current) when reading SPD datasheets — the two are tested to entirely different stress regimes and are not interchangeable ratings.
- Assuming the numeric current value an SPD needs to be rated to can be derived from C.2.2 alone — this clause only sets the class (I/D1 vs II/C2); the actual amperage comes from IEC 62305-2:2024 Annex B.
Design checklist
- Has the source of damage (S1-S4) at this specific SPD position been established from Figure C.1 / the related topic?
- Does the structure carry an external LPS, or is direct-lightning protection otherwise specified? If yes, has class I/D1 been specified at the relevant entrance SPD(s) without exception?
- If there is no external LPS, has the credibility of a direct/partial strike to the incoming overhead line (last pole to entrance) been assessed, and class I/D1 applied at or near the origin if that risk is real?
- For every secondary, equipment-proximate SPD (Figure C.1 items 2 and 4), has the oscillation/induction exposure at that specific position been checked to confirm class II/C2 is sufficient, rather than defaulting without review?
- Where class I is being waived on S1/S3 grounds alone, has the NOTE 1 frequency condition (ND + NL + NDJ ≤ 0,01/year) actually been checked against the site's IEC 62305-2 risk assessment, rather than assumed?
- Has the correct telecom-line equivalent (D1 for class I, C2 for class II) been specified for any telecommunication or signal-line SPD, matching the power-line classification logic?
- Has the classification decision (class I/D1 or II/C2) been carried forward correctly into the IEC 62305-2:2024 Annex B lookup for the actual Iimp/In numeric rating?
IEC 62305-4:2024 · LPES Knowledge Hub H-50
Selecting SPDs by voltage protection level Up
Rule No. 1 is the simplified method IEC 62305-4:2024 gives for choosing the voltage protection level Up of a surge protective device (SPD) without doing a full detailed analysis. It works by matching the SPD's Up against a required rated impulse voltage Uw read off Table C.1 for the equipment's nominal supply voltage and overvoltage category, applying an 80% safety margin when the protected equipment sits within 10 m of the SPD, keeping the connecting leads to the SPD to within roughly 0,5 m of total length (or compensating if they cannot be), and adding extra protective measures — a second SPD close to the equipment, or a more conservative Up — when the equipment is more than 10 m from the entrance SPD. It is the rule of thumb the standard permits "for general applications"; Rule No. 2 is the fuller calculation used when that level of approximation is not enough.
How it is applied
- Read the equipment's nominal supply voltage (or the voltage line-to-neutral) and find the corresponding required rated impulse voltage Uw from Table C.1, at overvoltage category II unless the equipment is specifically rated for the reduced category I.
- Select an SPD whose voltage protection level Up does not exceed Uw under any circumstance (the absolute ceiling from C.2.3.1.1).
- Determine the cable distance between the SPD (typically at the service entrance) and the equipment being protected:
- If ≤10 m: apply the 80% margin — choose Up ≤ 0,8 x Uw — unless the equipment connects directly to the SPD terminals, the Figure C.2 arrangement is used, or the OCPD's own voltage drop is already accounted for in Up.
- If >10 m: add one of the three C.2.3.1.4 measures (a second SPD near the equipment at Up ≤ Uw; one-port SPDs at the origin at Up ≤ 0,5 Uw plus shielded wiring; or two-port SPDs at the origin at Up ≤ Uw plus shielded wiring).
- Check the SPD assembly's total connecting-lead length (live conductor to PE conductor, summed over all connections and any disconnector). Keep it to ≤0,5 m. If it cannot be kept to ≤0,5 m, choose one of the three C.2.3.1.3 remedies (lower-Up SPD; a second coordinated SPD near the equipment; or the Figure C.2 arrangement).
- Where internal-system failure would be critical, additionally verify Up/f ≤ 0,5 Uw to allow for oscillatory voltage doubling on an open circuit at the equipment terminals.
- If none of these simplified checks can be satisfied with a single, sensibly specified SPD, or if formal demonstration of the protection level is required, move to Rule No. 2 for the full ΔU/kr/Vi calculation.
Common mistakes
- Treating Up ≤ Uw (the absolute ceiling) as sufficient on its own and forgetting the additional 80% margin that applies whenever the equipment is within 10 m of the SPD — the source is explicit that the margin "shall in no case" be skipped except under the three named exemptions.
- Measuring "lead length" as only the length of one conductor, rather than as required by C.2.3.1.3: "the sum of the path length of conductors used from the live conductor to the PE conductor" — i.e. the full loop, not a single run.
- Applying the >10 m one-port limit (Up ≤ 0,5 Uw) to a two-port SPD, or vice versa — the source ties the tighter 50% figure specifically to the one-port case because of propagation/dU-dt effects that a two-port SPD's series impedance is expected to have already reduced.
- Selecting Up purely from Table C.1's overvoltage category II column without checking whether the actual equipment is instead specified to the reduced category I column, which the same table also provides.
- Forgetting the Up/f ≤ 0,5 Uw criticality check for internal systems where failure would be critical — Rule No. 1's headline 80%/Table C.1 checks alone do not cover the oscillatory voltage-doubling case that this separate criterion addresses.
- Assuming Rule No. 1 always suffices: where formal "demonstration of SPD protection is needed" the standard directs the designer to Rule No. 2 instead.
Design checklist
- Nominal supply voltage / voltage line-to-neutral identified and matched to the correct row of Table C.1.
- Required Uw read off Table C.1 at the correct overvoltage category (II unless the equipment is rated for reduced category I).
- Chosen SPD's Up confirmed to never exceed Uw under any circumstance.
- Cable distance from SPD to protected equipment measured and classified as ≤10 m or >10 m.
- If ≤10 m: Up ≤ 0,8 x Uw confirmed, or one of the three named exemptions documented and justified.
- If >10 m: one of the three C.2.3.1.4 measures selected and its own Up ceiling (Uw, or 0,5 Uw for one-port) applied; shielded wiring specified where the one-port or two-port origin-SPD option is used.
- Total connecting-lead length (live conductor to PE conductor, summed) checked against the 0,5 m target; a remedy (lower-Up SPD, second coordinated SPD, or Figure C.2 arrangement) selected if it is exceeded.
- Up/f ≤ 0,5 Uw checked wherever internal-system failure would be critical.
- Where any of the above cannot be satisfied confidently with Rule No. 1, escalation to Rule No. 2 recorded.
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
- Bonding done at the board but not where services enter the building
- Type 2 devices used where a Type 1 is required
- Isolating joints and insulated flanges left without spark gaps
- Monitoring fitted with nobody assigned to act on alarms
- Records kept by the contractor and never handed to the owner
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 62305-3 and -4:2024 (Ed. 3) · IEC 61643 series · IEC 60364-6:2016 · IS 3043:2026 · IS 732:2019 · 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 do Type 1, 2 and 3 mean?
Type 1 diverts partial lightning current at the service entry, Type 2 limits surges at distribution boards and Type 3 gives fine protection at the equipment. Type 1 Lightning-current Arresters
Do I need all three types?
With an external LPS or overhead supply, a Type 1 is needed at the entry. Type 2 and 3 follow wherever distance or equipment sensitivity requires. SPD Coordination Design
Why do lead lengths matter?
Every extra length of connecting lead adds voltage on top of the SPD's protection level. Keep the total at 0.5 m or less. Type 2 SPDs
Are data lines included?
Yes. Any conductor crossing a zone boundary carries surges, including network, signal and antenna cables. Data, Signal & RF Line SPDs
What if there is no space in the board?
A pre-wired SPD panel is mounted beside the board and connected with short leads. SPD Panels & Surge Boxes
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.
