IS 7098:1985 Part 2 is the Indian Standard (BIS) for cross-linked polyethylene insulated pvc sheathed cables for working voltages from 3.3 kv up to and including 33 kv. This standard specifies the requirements for cross-linked polyethylene (XLPE) insulated and PVC sheathed cables for medium and high voltage power distribution. It covers both single and three-core cables, armoured and unarmoured, for working voltages from 3.3 kV up to 33 kV. Note: This 1985 version has been superseded by the 2011 revision.
Specifies requirements for XLPE insulated, PVC sheathed cables with copper or aluminium conductors for high voltage applications (3.3 kV to 33 kV).
Key reference values — verify against the current code edition / project specification.
| Reference | Value | Clause |
|---|---|---|
| Subject | XLPE-insulated PVC-sheathed cables, 3.3–33 kV | Scope |
| Insulation | XLPE — 90 °C continuous / 250 °C short-circuit | Property |
| Screening | Conductor & insulation semicon + metallic screen | Construction |
| Voltage grades | 3.3 / 6.6 / 11 / 22 / 33 kV | Ratings |
| Testing | Partial discharge, HV, IS 10810 routine/type | QC |
| Read with | IS 7098 Part 1 (≤1.1 kV) / IS 3961 / IS 1255 | Cross-ref |
BIM-relevant code. See the BIM Hub for ISO 19650, IFC, and LOD/LOIN frameworks used alongside it.
IS 7098 (Part 2):1985 is the Indian Standard for Cross-Linked Polyethylene (XLPE) Insulated Thermoplastic Sheathed Cables for Working Voltages from 3.3 kV up to and including 33 kV. It covers the medium-voltage (MV) power cables that distribute electricity from substations to industrial / commercial customers + form the backbone of urban distribution networks.
Use it when: - Specifying MV cables for substation interconnections, large industrial / commercial customers, MV feeders - Procuring cables for renewable-energy projects — wind farms, solar parks - Auditing cable supply — conductor cross-section, insulation thickness, sheath, dimensions - Selecting cables for buried / overhead / submarine applications — different installation conditions need different cable types - Investigating cable failures — insulation breakdown, sheath damage, termination issues
IS 7098 series structure: - IS 7098 Part 1:1988 — Low voltage XLPE cables (0.6/1.1 kV) - IS 7098 Part 2:1985 (this code) — Medium voltage XLPE cables (3.3-33 kV) - IS 7098 Part 3:1993 — High voltage XLPE cables (above 33 kV up to 66 kV) - IS 7098 Part 4:2009 — Ultra-high voltage XLPE cables (above 66 kV)
IS 7098 Part 2 is the dominant code for the MV distribution segment in India — most urban / industrial power-supply cables fall under this specification.
XLPE advantages over PVC (older insulation): - Higher continuous operating temperature (90°C vs 70°C for PVC) - Higher overload temperature (130°C for 1 hour, vs 100°C for PVC) - Better dielectric properties — lower losses + higher voltage capability per unit thickness - Better mechanical properties — more durable, more flexible - Longer service life (30-40+ years for proper XLPE)
Layered structure (Clause 5):
1. Conductor — copper (Class 2 stranded round per IS 8130) or aluminium (Class 2 stranded round per IS 8130). Cross-sections: 25 mm² to 1000 mm² (most commonly 70, 95, 120, 185, 240, 300, 400, 500 mm²).
2. Conductor screen — semi-conductive XLPE layer; ensures uniform electrical field around conductor; thickness 0.4-0.7 mm.
3. Insulation — XLPE (cross-linked polyethylene); thickness varies by voltage: - 3.3 kV (E): 2.5 mm - 6.6 kV (E): 3.4 mm - 11 kV (E): 3.4 mm - 22 kV (E): 5.5 mm - 33 kV (E): 8.0 mm
4. Insulation screen — semi-conductive XLPE; thickness 0.4-0.7 mm.
5. Metallic screen — copper tape (helically wrapped) or copper wire braid; for earth-fault current return + electrostatic shielding.
6. Inner sheath / bedding (optional) — protective layer; rubber or PVC.
7. Armouring (optional) — for mechanical protection where required: - Galvanized steel wire armour (GSWA): for buried + heavy mechanical stress - Aluminium wire armour (AWA): for non-magnetic applications, alternative current routing - Steel tape armour: for laying in conduit
8. Outer sheath — PVC (PVCs1 grade per IS 5831); thickness varies by cable size.
Acceptance criteria (Clauses 6-15): - Dimensional check: conductor + insulation + sheath thicknesses per spec - Insulation resistance: ≥ 10,000 MΩ-km at 27°C - High-voltage withstand test: applied at 3.5× rated voltage for 5 minutes; no insulation breakdown - Mechanical tests: bending, twisting, abrasion resistance on sheath - Thermal aging: 168 hours at 100°C for XLPE compounds; verify properties retention - Cold impact test: at -25°C; sheath should not crack - Conductor resistance: per IS 8130 conductor-class requirements - Surface defect check: visual inspection for sheath / armour quality
Voltage rating system (U₀/U): - U₀ = phase-to-ground voltage; primary rating - U = phase-to-phase voltage - E = lightning impulse withstand voltage
Common Indian voltage levels: - 3.3 kV (E) → U₀/U = 1.9/3.3 kV; for some industrial / specific applications - 6.6 kV (E) → 3.6/6.6 kV; older legacy systems - 11 kV (E) → 6.35/11 kV; most common Indian MV distribution voltage - 22 kV (E) → 12.7/22 kV; for some metro / industrial / large customer feeders - 33 kV (E) → 19/33 kV; sub-transmission level
Conductor selection: - Copper: better conductivity per unit area; smaller cable for same capacity - Aluminium: lighter, cheaper; larger cable for same capacity. Increasingly preferred in India for distribution (cost + lifecycle)
Cross-section vs ampacity (typical, for 11 kV cable in air): - 70 mm² Cu: ~200 A - 95 mm² Cu: ~240 A - 120 mm² Cu: ~280 A - 240 mm² Cu: ~420 A - 95 mm² Al: ~170 A - 240 mm² Al: ~325 A
Derating factors apply for: - Buried installation: 0.8-0.95 (depending on soil type + temperature) - Group laying: 0.7-0.95 (depending on number + spacing) - High ambient temperature: 0.6-0.95 (per 10°C above 30°C)
Typical applications: - Substation tie-feeders: 11 kV (E), 240-400 mm² Al, single-core or three-core - Industrial customer service: 11 kV (E), 95-185 mm² Al - Wind farm collection: 33 kV (E), 240-500 mm² Cu/Al, often single-core - Solar park MV grid: 33 kV (E), 185-400 mm² Cu/Al - Urban substation interconnections: 11 kV (E) or 22 kV (E), single or three-core
1. Wrong voltage class for application — using 11 kV cable on 22 kV system causes catastrophic insulation breakdown. Always verify nameplate voltage rating matches system voltage.
2. Inadequate ampacity — cable selected for nominal load without considering ambient temperature, group derating, and harmonic factors. Use cable manufacturer's detailed ampacity tables + IS 7098 derating curves.
3. Wrong armour type — using AWA in DC traction system creates eddy current losses + heating. Use GSWA for AC systems; AWA only for specific non-magnetic requirements.
4. Bending radius violation — bending XLPE cable tighter than minimum bend radius (typically 12-15× cable OD) damages insulation. Calculate minimum bend radius from manufacturer specification.
5. Poor cable termination — cable terminations (heat-shrink, cold-shrink, premoulded) must follow exact manufacturer's procedure. Improper termination → moisture ingress → eventual failure (sometimes years after installation).
6. No moisture barrier at cable joints — cable joints exposed to water cause progressive degradation. Use hermetic joints (heat-shrink or epoxy-injection) + waterproof enclosure.
7. Mixed-source cables in same circuit — different manufacturers, different XLPE batches have slightly different aging behaviour. For long-life applications (substation tie-feeders, > 20-year design), single-source preferred.
8. Inadequate identification + tagging — buried cables without warning tapes / markers + above-ground without cable tag get damaged during excavation OR are wrongly identified. Provide warning tape 300 mm above buried cable; metallic tag with cable ID at every termination + joint.
9. No earth fault calculation — under fault conditions, the cable must withstand high fault currents (10-20× rated) for protection clearing time (typically 0.5-3 seconds). Verify cable thermal withstand against protection coordination.
10. Skipping IS 8130 conductor verification — copper / aluminium conductor must meet IS 8130 stranding + resistance requirements. Some unbranded cables use undersized conductors saving 10-15% material cost; ampacity is compromised.
11. No commissioning test — every new cable installation requires: - Insulation resistance test (IR test) at 1, 5 minutes (megger-meter) - High-voltage AC test or DC withstand test (factory-acceptance + site recommissioning) - Verify earth continuity - Phase-rotation check
IS 7098 Part 2:1985 is 40 years old but methodologically aligned with international practice (IEC 60502-2). The XLPE chemistry + cable construction principles are mature. Minor amendments since 1985 have refined acceptance tests + added specialty cable types.
Indian MV cable market: - Major manufacturers (Polycab, KEI Industries, Universal Cables, Havells / Sigma, Finolex, Bonton): consistent IS 7098 Part 2 conformance, export-quality, multiple manufacturing facilities. Cost premium ~15-30% over budget brands; quality consistency dramatically better. - Mid-tier manufacturers (numerous): variable quality. Pre-qualify with sample testing + factory audit. Cost 10-20% lower than premium. - Imported cables (Brugg Cables, Prysmian, Nexans via Indian distributors): premium pricing; specialty / high-voltage applications.
Procurement reality: - Major utility tenders (NTPC, PowerGrid, DISCOMs): typically specify IS 7098 Part 2 + IEC 60502-2 dual conformance; Material Test Certificates per batch; site acceptance testing - Industrial customer purchases: IS 7098 Part 2 specified; cost-competitive among premium brands; commissioning tests after installation - Renewable energy projects (wind, solar): typically specify higher-grade cables (33 kV E with armour); long lead-times for special configurations
Cost reality (2026 typical Indian market): - 11 kV three-core 240 mm² Al cable: ₹400-700/m - 11 kV three-core 95 mm² Cu cable: ₹600-1,000/m - 33 kV three-core 240 mm² Al cable: ₹700-1,200/m - 33 kV three-core 240 mm² Cu cable: ₹1,200-2,000/m - Installation cost (cable laying, terminations, jointing): ₹400-800/m typically
For specifying engineers: - Always specify: standard (IS 7098 Part 2), voltage rating (E, kV/kV), conductor type (Cu/Al), cross-section (mm²), construction (single-core / 3-core), armour type, sheath type - Mandate batch-level Material Test Certificate - Site acceptance test (IR + HV withstand) before energization - Specify cable terminations to manufacturer's procedure - For premium applications: NABL-accredited cable testing certificate
Quality assurance during installation: - Visual inspection: no damage during transport / handling; manufacturer date < 6 months ideally - Insulation resistance check on each cable before laying - Mechanical protection during laying (sand bedding, warning tape, RCC protection slab over) - Termination per manufacturer's procedure (specialist installation) - Final commissioning: IR test + HV withstand at site
Future direction: - Higher-voltage applications: 220 kV / 400 kV XLPE cables for renewable grid integration - Submarine cables: separate IS in development; for off-shore wind / inter-island connectivity - High-temperature cables: 105°C continuous-rated XLPE for higher ampacity - Fire-resistant cables (IS 11731:1986 — for evacuation routes + tunnel applications)
IS 7098 series is a stable, mature specification. The market is sophisticated; cable quality is dependable from premium manufacturers; commissioning practices are well-established.