Sector applications · Complies to IEC 62305-4
Data Centre, Hospital and Critical Facility Protection
Data centres, hospitals and other critical facilities cannot accept downtime or damaged electronics. Protection follows the lightning protection zone concept: a bonded earthing network, coordinated surge protection from the main incomer to the rack or medical location, and continuous monitoring of the devices.
When it applies
- Data centres and server rooms
- Hospitals, operating theatres and diagnostic imaging
- Pharmaceutical production and laboratories
- Control rooms, banks and emergency services
When it does not
- Buildings without continuous-operation requirements, where a basic two-stage SPD scheme is enough
- The external LPS, which is designed from the structure solutions
- Medical IT systems themselves, which are specified by the electrical designer
How the system works
- AssessA lightning risk assessment and the sector's own standard set the protection level.
- Earth and bondEvery structure, frame and cabinet is joined to one earthing system.
- Protect the linesCoordinated surge protective devices are fitted on power, DC, RF and data lines.
- Monitor and maintainCounters and status contacts show what happened; inspection keeps the system in service.
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 |
|---|---|---|
| Zone concept | Lightning protection zones defined; every line bonded or protected at each boundary | IEC 62305-4 |
| Bonding network | Meshed bonding network under raised floors and in technical rooms, tied to the main earthing terminal | IEC 62305-4 · TIA-942 |
| Main incomer | Type 1+2 SPD rated for the protection level | IEC 61643-11 · IEC 60364-5-534 |
| Sub-distribution and UPS | Type 2 SPDs at floor boards and at UPS input and output | IEC 60364-5-534 |
| Equipment level | Type 3 SPDs at rack power strips and sensitive loads; data-line SPDs at zone boundaries | IEC 61643-11 · IEC 61643-21 |
| Medical locations | Supplementary equipotential bonding in Group 1 and 2 rooms | IEC 60364-7-710 |
| Monitoring | Remote status contacts on every SPD brought to the building management system | IEC 62305-4 |
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+2 Combined SPDs | Combined arrester at the main LV incomer | One set per incomer |
| Type 2 SPDs | Surge protection at sub-distribution boards and UPS | One set per board and per UPS input and output |
| Data, Signal & RF Line SPDs | Protection of data, signal and communication lines | One per line at each zone boundary |
| Earth Bars & Terminals | Main and local bonding bars for the meshed bonding network | One per technical room, floor and riser |
| SPD Monitoring | Status monitoring of all SPDs | One monitor per board or group of SPDs |
From design to handover
- Define the lightning protection zones and list every incoming line
- Design the bonding network and the SPD schedule with coordination
- Install SPDs with short connecting leads and bond all services
- Connect status contacts to the building management system
- Verify, document and put the system under periodic audit
Services for this solution
SPD Coordination DesignSPD Health AuditAnnual Maintenance Contract
Industries that use it
What the standards require
Checked against the current editions held in the LPES standards library.
- IEC 62305-2:2024
- Risk to life and physical damage is compared with a tolerable risk of 10⁻⁵ per year; failure of internal systems is judged separately as a frequency.
- 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.
- CEA Safety Regulations 2023, Reg. 38(3)
- Lightning protection is addressed for multi-storeyed buildings above 15 m and listed public premises such as airports, hospitals and hotels.
- IEEE 80-2013
- A substation grid is judged by touch and step voltage against the tolerable limits, not by its resistance alone.
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 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. |
| IS 3043:2026 | Clause 11.2 | Medical locations use TN-S, with a medical IT system in Group 2. Protective conductor impedance from the bonding bar to a socket is at most 0.2 Ω and from an extraneous part to the bonding bar at most 0.1 Ω. Dedicated clean earths are not permitted. |
| IS 3043:2026 | Clause 11.1 | For industrial and commercial premises a global earthing system is recommended, and it is mandatory where a high-voltage substation stands on the premises. Low-voltage distribution is TN-S, with the source neutral earthed once. |
| 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 43(v) | Every building shall have protective equipotential bonding that interconnects exposed and extraneous conductive parts. |
| IS 732:2019 · IEC 60364-4-41 | 4.2.11 | For automatic disconnection at 230 V to earth, final circuits disconnect within 0.4 s in TN systems and 0.2 s in TT systems. Distribution circuits may take up to 5 s in TN and 1 s in TT. |
| IEC 60364-6:2016 · IS 732:2019 | 6.4.3.7.3, Annex D | A measured earth-fault loop impedance is accepted when it is not more than two thirds of U0 ÷ Ia, where Ia is the current that operates the device in the required time. The margin covers conductor heating under fault. |
| 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. |
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-12
Integrating internal systems into the bonding network (star vs meshed)
Once a structure has a bonding network, every piece of equipment sitting inside that network still has to be connected into it in a disciplined way, or the benefit of the network is undone by long, badly routed connecting leads. IEC 62305-4:2024, 5.3 gives two ways to make that connection: a star configuration, where every conductive part of the internal systems in a zone is isolated from the earthing system and brought to one single bonding point acting as an earthing reference point (ERP) - this is called type Ss; and a meshed configuration, where the same conductive parts are bonded directly into the bonding network at many points - this is called type MM. A small zone with all lines entering at one point takes configuration S; a wide zone, a whole structure, or a zone with many lines entering at several points takes configuration M; and a complex system combines both, which the standard names Combination 1 (Ss combined with MM) and Combination 2 (Ms combined with MM).
How it is applied
- Establish the LPZ and its physical extent and identify every internal system whose conductive parts (cabinets, enclosures, racks) and PE conductor need to be integrated into the zone's bonding network.
- For each system, check how many points it needs to enter the zone at, and how large the zone is:
- one entry point, relatively small zone -> configuration S is applicable.
- a wide zone, a whole structure, or several entry points -> configuration M is applicable.
- If configuration S is chosen: isolate every metal component of that system from the earthing system, terminate the isolation at a single bonding bar (the ERP), and route every line between the system's individual units in parallel with, and close to, the star's bonding conductors, specifically to avoid induction loops.
- If configuration M is chosen: bond the metal components into the earthing system at multiple points rather than isolating them, giving type MM.
- Where a single facility mixes small, single-entry sub-systems with a wide, multi-entry system, combine the two per Figure 10: Combination 1 (Ss + MM) where the star sub-system's ERP itself sits on the meshed network, or Combination 2 (Ms + MM) where the star-referenced meshed sub-system (Ms) is combined with a directly meshed sub-system (MM).
- Hand the physical bonding points from Steps 3-5 to H-13 (bonding-bar installation rules) and size every bonding conductor per H-15 (Table 1, minimum cross-sections).
Common mistakes
- Using configuration M (multiple bonding points, no isolation) for a small, single-entry cabinet "to be safe": this defeats the purpose of the star arrangement and can reopen induction loops the standard specifically asks the star wiring discipline to avoid.
- Using configuration S for a distributed, multi-entry system: a star scheme forces every line back to one ERP, which for a wide zone with several entries means long parallel runs that themselves become large loops - exactly what configuration M is designed to prevent for that geometry.
- Isolating the metal components under configuration S but not routing the equipment's cabling in parallel with, and close to, the star's bonding conductors: the standard makes both parts of the rule (isolation and cabling parallel to the star conductors) conditions of a correct type-Ss installation, not the isolation alone.
- Treating "type Ss" and "type Ms" as the same thing: Ss is the pure star result of configuration S; Ms is a meshed configuration integrated via an earthing reference point, used specifically in Combination 2 - the two are not interchangeable labels.
- Forgetting that the PE conductor of the internal system is itself subject to this same configuration choice, and connecting it to the bonding network by a separate, ad-hoc route.
Design checklist
- Has every internal system's conductive parts and PE conductor been assigned to either configuration S or configuration M, per zone?
- For each zone assessed as configuration S: is it relatively small, and does every line enter at one point only?
- For each zone assessed as configuration M: is it a wide zone, a whole structure, or a zone with several entry points and many inter-equipment lines?
- Under configuration S, are all metal components of the system isolated from the earthing system except at the single ERP?
- Under configuration S, do all lines between individual equipment run in parallel with, and close to, the star's bonding conductors?
- Under configuration M, are the metal components bonded into the earthing system at multiple points, with no isolation?
- Where both configurations coexist in one facility, has the combination been identified correctly as Combination 1 (Ss + MM) or Combination 2 (Ms + MM)?
- Have the resulting bonding points been handed to the bonding-bar installation rules (H-13) and the minimum cross-sections (H-15)?
IEC 62305-4:2024 · LPES Knowledge Hub H-52
SPD arrangements: single entrance SPD, two coordinated SPDs (SPD1 + SPD2), and equipment connected to two services (Figure C.4)
Once an SPD's location has been fixed by source of damage (Clause C.2.1) and itscurrent and voltage ratings are being worked out (C.2.2-C.2.3), Annex C still hasto answer a third, purely topological question: how many SPDs, arranged how, doesthis particular piece of equipment actually need? Clauses C.2.4 to C.2.6 answerthat in three steps: sometimes a single SPD at the service entrance is enough(C.2.4); sometimes a coordinated pair - SPD1 at the entrance and SPD2 near theequipment - is required because sources S1 or S3 cannot be neglected (C.2.5); andwhere the same equipment is fed by two different services (e.g. power andsignal), Figure C.4 sets out the earthing and bonding rules that stop the twoSPDs from fighting each other through a non-equipotential earthing system (C.2.6).
How it is applied
- Step 1: confirm SPD location(s) from Figure C.1 and confirm whether sources S1 or S3 can be neglected for this structure (from the risk assessment).
- Step 2: if S1 and S3 can both be neglected, C.2.4 allows a single SPD at the service entrance to be sufficient - select and rate it per C.2.2/C.2.3 and stop here.
- Step 3: if S1 or S3 (or both) cannot be neglected, build a two-SPD coordinated arrangement per C.2.5: SPD1 at or as close as possible to the service entrance (e.g. main distribution board), rated per C.2.2 for class I/D1 or class II/C2 as applicable, with leads/connections <= 0,5 m; SPD2 near the equipment input, tested to class II (power) or C2 (telecommunication/signal), with leads/ connections <= 0,5 m.
- Step 4: identify every other metallic service feeding the same equipment (e.g. a telecommunication line alongside the power line). Per C.2.6, install additional SPDs on those services too, UNLESS that service originates inside the structure, or enters via an isolation interface - in which case the additional SPD may not be required.
- Step 5: where SPDs sit on two different ports/services of the same equipment (Figure C.4), check the earthing arrangement.
- If the two SPDs' earthing points are NOT equipotential, apply one of the four accepted fixes: (a) a densely meshed foundation earth electrode or a ring electrode bonded to the steel reinforcement; (b) shield or route the internal services inside a metallic duct bonded to the BB at one end and the equipment earth at the other; (c) improve the transient response of an existing single-conductor BB-to-BB bond by connecting the earthing ring electrode to the structure's steel reinforcement; or (d) install a multiservice SPD between the two ports, rated to withstand an S1 or S3 event or both.
Common mistakes
- Installing a two-SPD arrangement (SPD1+SPD2) as a default "best practice" even where S1 and S3 have been assessed as neglectable - C.2.4 explicitly allows a single entrance SPD to be sufficient in that case; over-specifying adds cost without adding required protection.
- Protecting the power line into a piece of equipment but leaving a telecommunication or signal line into the SAME equipment unprotected, without checking the two exemptions (service originates inside the structure; service enters via an isolation interface) that would justify leaving it unprotected.
- Installing SPDs on both the power and signal ports of a piece of equipment (Figure C.4) without checking whether the two SPDs' earthing points are actually equipotential - a non-equipotential arrangement can let a surge produce a damaging potential difference ACROSS the equipment even though each individual SPD is working correctly.
- Treating "there is a bonding connection between the two BBs" as automatically sufficient - C.2.6 explicitly flags that a single-conductor bond "is inadequate on its own to provide potential equalization" unless the transient response is improved (e.g. via the structure's steel reinforcement) or one of the other three remedies is used instead.
- Exceeding the 0,5 m lead-length guidance for SPD1 or SPD2 without compensating per the lead-length options covered in the related topic.
Design checklist
- Sources S1 and S3 assessed: can either be neglected for this structure?
- If both can be neglected: single SPD at service entrance selected and rated per C.2.2/C.2.3.
- If either cannot be neglected: SPD1 installed at/near the service entrance, SPD2 installed near the equipment input, both with leads/ connections kept to <=0,5 m where possible.
- Every metallic service feeding the equipment identified; additional SPDs installed on each, or the "originates inside the structure" / "enters via isolation interface" exemption documented for any service left unprotected.
- Where SPDs sit on two different ports of the same equipment (Figure C.4), earthing points checked for equipotentiality.
- If not equipotential: one of the four remedies applied and recorded (meshed/ring electrode bonding; shielded/metallic-duct service routing; improved single-conductor BB bond via steel reinforcement; multiservice SPD rated for S1/S3).
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.
Maximum earth-fault loop impedance
- Trip current Ia
- –
- Design limit for Zs
- –
- Without the 2/3 margin
- –
Zs ≤ (2 ÷ 3) × U0 ÷ Ia for miniature circuit breakers to IS/IEC 60898, instantaneous trip. Every circuit and every source is checked, as CEA Reg 43(xii) requires.
What we find on audits
- Equipment earths and lightning earths kept separate
- Surge protective devices chosen without coordination or the right voltage rating
- Long connecting leads that add kilovolts to the protection level
- Data and signal lines left unprotected while power lines are protected
- No inspection after a strike, so failed devices stay in service
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 62305-2, -3 and -4:2024 (Ed. 3) · IEC 61643 series · IEEE 80-2013 · IEC 61936-1:2021 · IS 3043:2026 · 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 surge protection does a data centre need?
A coordinated scheme: Type 1+2 at the main incomer, Type 2 at distribution boards and UPS, Type 3 at racks, and data-line SPDs at zone boundaries. SPD Coordination Design
Does a UPS protect against surges?
Not against lightning surges. SPDs are fitted at the UPS input and output to protect the UPS and its load. Type 2 SPDs
What is a meshed bonding network?
A grid of bonding conductors linking racks, floors, trays and bars so that all metalwork stays at nearly the same potential. Earth Bars & Terminals
How do I know when an SPD has failed?
Through its status indicator and a remote contact wired to the monitoring system. SPD Monitoring
How often should SPDs be checked?
At least once a year and after every known strike or major fault. SPD Health Audit
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.
