Systems and special applications · Complies to ISO 15589-1/-2 · NACE SP0169 · NACE SP0177
Cathodic Protection for Buried Steel
Cathodic protection stops corrosion of buried or immersed steel by making it the cathode of an electrochemical cell, using sacrificial anodes or an impressed current. It is applied with a coating and verified by measuring the structure-to-soil potential.
When it applies
- Buried steel pipelines for oil, gas and water
- Tank bottoms and buried vessels
- Jetties, sheet piles and other marine steel
- Earthing grids and well casings in corrosive soil, by design
When it does not
- Above-ground steel, which is protected by coating
- Structures that are not electrically continuous
- Design without soil resistivity and coating data
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 |
|---|---|---|
| Protection criterion | Structure-to-soil potential of −850 mV or more negative against a copper/copper-sulphate electrode | ISO 15589-1 |
| Limit | Not more negative than about −1,200 mV, to avoid coating damage | ISO 15589-1 |
| Current demand | From surface area, coating quality and soil resistivity | ISO 15589-1 |
| System type | Sacrificial anodes for small or well-coated structures; impressed current for large ones | ISO 15589-1 |
| Electrical isolation | Isolating joints, protected by isolating spark gaps against lightning and fault voltage | ISO 15589-1 · IEC 62561-3 |
| Test stations | At regular intervals and at crossings and isolating joints | ISO 15589-1 |
| AC interference | Assessed where pipelines run near power lines | ISO 18086 |
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 |
|---|---|---|
| Cathodic Protection | Anodes, backfill, transformer-rectifiers, test stations and reference electrodes | From the current-demand calculation and the route |
| Corrosion Protection & Sealing | Tapes, sealants and coatings for joints and soil transitions | One per joint and per transition |
| Isolating Spark Gaps | Protect isolating joints and decouple earthing systems | One per isolating joint |
From design to handover
- Survey soil resistivity, coating condition and existing potentials
- Calculate current demand and choose sacrificial or impressed current
- Install anodes, cables, test stations and isolating spark gaps
- Commission and adjust to the protection criterion
- Survey potentials periodically and keep the 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 62305-4:2024
- 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 3043:2026 | Clause 11.4 | In hazardous areas only TN-S is used inside the area, potential equalisation covers Zones 0, 1 and 2 with supplementary bonding of at least 10 mm² copper, pipe racks are bonded every 25 m, and pipelines are bonded at entry and exit with respect for cathodic protection. Separate electrodes are not allowed. |
| 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. |
| 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 | 10.2.2 | 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. |
| 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 62305-3:2024 · LPES Knowledge Hub H-41
Bonding of external conductive parts and isolating spark gaps
Every structure with a lightning protection system also has metal that was never designed as part of it: incoming water and gas pipework, metallic cable screens, and other extensive metal items. When lightning current flows in the external LPS or along one of these items, each can rise to a different potential, and if two are close enough the difference can flash over and cause dangerous sparking inside the structure. Lightning equipotential bonding closes that gap for conductive parts entering or leaving the structure, normally by a direct bonding conductor; where a direct metallic connection cannot be allowed — most often because the pipework carries cathodic protection or must stay electrically isolated — an isolating spark gap (ISG) is used instead, open in normal service and bonded only during the transient that matters.
How it is applied
- Identify every external conductive part and line entering/leaving the structure: pipework (water, gas, fuel, process), cable screens/conduits, and other extensive metal items.
- For each, check whether the separation distance (6.3) can be kept. If not — the normal case at a point of entry — bonding under 6.2 is required.
- Locate the bonding point as near as possible to the point of entry (6.2.3), routed to a bonding bar near the earth-termination system, positioned for inspection; use a ring bonding bar or interconnected bars for large structures.
- Choose the interconnecting means: a bonding conductor sized to Table 9 where a direct, permanent connection is acceptable to all parties; an SPD for live conductors; an ISG where a direct bond is not allowed at all (cathodic protection, hazardous-area isolation, or an operator's refusal).
- Where an ISG is selected, size it against Iimp ≥ IF and Uimp below the insulation's withstand level, confirm testing to IEC 62561-3, and add rating per IEC 60079-14 across a hazardous-area boundary.
- Coordinate the chosen method with every operator concerned before installation (6.2.1) — a mandatory discussion, not a decision the LPS designer makes alone.
- For screened/conduit cables, calculate SCMIN from Annex A; add an SPD between the screen and active conductors if the installed cross-section falls short.
- Verify on completion that connections are direct and straight, SPDs remain accessible, and any ISG bridging a cathodic-protection joint is correctly matched and agreed with the pipework's operator.
Common mistakes
- Bonding a live conductor directly instead of through an SPD, or forcing a direct bond onto a pipe that must stay isolated for cathodic protection, defeating the corrosion-protection system.
- Selecting an ISG on breakdown voltage alone, without confirming Iimp is not less than IF for the part it protects.
- Directly bonding a galvanized-steel earth electrode to reinforcement, or a cathodic-protection isolating joint, in soil — the standard's materials guidance (D.5.6.2.2) records that this increases corrosion risk and calls for an ISG instead.
- Locating the bonding point well inside the structure rather than as near as possible to the point of entry (6.2.3).
- Sizing an external-conductive-part bonding conductor to the lighter Table 10 values instead of Table 9.
- Choosing the bonding method without the mandatory discussion with the gas, water, telecom or power operator (6.2.1).
- Assuming a bonded cable screen removes the need for an SPD without checking its cross-section against SCMIN from Annex A.
- Confusing an ISG (a bonding-and-isolation component, 3.36) with an isolated or electrically insulated LPS (3.3/3.5) — related concepts, not the same measure.
Design checklist
- All external conductive parts and lines entering/leaving the structure identified.
- For each, the choice between separation distance (6.3) and bonding (6.2) made and recorded.
- Bonding point as near as possible to the point of entry, tied to a bonding bar near the earth-termination system.
- Correct interconnecting means chosen per part: bonding conductor / SPD (live conductors) / ISG (where direct bonding is not allowed).
- Every ISG: tested to IEC 62561-3; Iimp ≥ IF; Uimp below the insulation withstand level; additionally rated per IEC 60079-14 if in a hazardous area.
- Every bonding conductor sized to Table 9 or Table 10 as appropriate, installed direct and straight; every SPD installed so it can be inspected.
- Screened/conduit cables checked against SCMIN (Annex A); SPD added where the installed cross-section falls short.
- Bonding method for each utility-owned part discussed and agreed with that operator.
- Buried or embedded connections at corrosion risk (galvanized steel to reinforcement, cathodic-protection joints) use an ISG, not a direct bond.
- Tall structures (over 30 m): equipotential bonding repeated at 20 m intervals.
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
Sacrificial anode or impressed current?
Sacrificial anodes suit small or well-coated structures in low-resistivity soil. Impressed current suits long pipelines and large structures. Cathodic Protection
How is protection confirmed?
By measuring the structure-to-soil potential against a reference electrode and comparing it with the −850 mV criterion. Installation & Commissioning
Why fit a spark gap across an isolating joint?
Lightning or a power fault can flash over the joint and damage it. The spark gap conducts during the event and isolates again afterwards. Isolating Spark Gaps
Is coating still needed with cathodic protection?
Yes. Coating reduces the current demand; cathodic protection covers the defects in the coating. Corrosion Protection & Sealing
Can an existing design be reviewed?
Yes, through a third-party design peer review. Third-party Design Peer Review
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.
