Reference · IS 694:2010 · IEC 60228 · BIS · Technical Terms
Cable Technical
Glossary.
Every technical term used in cable specification, procurement, and installation — defined precisely, in plain language. From BIS to OI, from Class 5 to FR-LSH. This is the reference document for Indian cable buyers, specifiers, and electrical engineers.
Standards and Organisations
BIS, IEC, IS, and the regulatory framework.
| Term | Definition |
|---|---|
| BIS | Bureau of Indian Standards — the national standards body of India. Issues IS standards and grants BIS licences to manufacturers. A valid BIS licence is the legal authority to mark a cable with the ISI mark. |
| ISI Mark | The certification mark of BIS, indicating that a product has been independently tested and found to comply with the relevant Indian Standard. For cables, the ISI mark on the sheath (or reel) confirms BIS IS 694:2010 or IS 17048:2018 compliance. |
| BIS Licence | A licence granted by BIS to a specific manufacturer at a specific factory address, permitting them to produce and mark cable to a particular IS standard. The licence number (e.g., CM/L-XXXXXXXX) appears on cable packaging and test certificates. Buyers can verify licence validity on the BIS portal. |
| IS 694:2010 | Indian Standard for PVC insulated cables and flexible cords for voltages not exceeding 1100V. Governs FR, FR-LSH, single core, multicore, control cable, submersible cable, and flexible wire. Amended by Amendments 1–4. |
| IS 17048:2018 | Indian Standard for halogen-free flame-retardant insulated cables and flexible cords for voltages not exceeding 1100V. Governs LSZH / HFFR cable. Separate BIS licence required — IS 17048:2018 cable cannot be supplied under an IS 694:2010 licence. |
| IS 8130:2013 | Indian Standard for conductors for insulated electric cables and flexible cords. Equivalent to IEC 60228:2004. Defines Class 1 (solid), Class 2 (stranded), Class 5 (fine-stranded), and Class 6 conductor requirements including strand count and maximum resistance. |
| IS 5831:1984 | Indian Standard for PVC insulation and sheath of electric cables. Defines compound types: Type A (70°C general), Type C (85°C heat-resistant), Type D (85°C), ST1/ST2/ST3 (sheath grades). Referenced by IS 694:2010. |
| IEC | International Electrotechnical Commission — the international standards body for electrical technology. IEC standards (IEC 60228, IEC 60227, IEC 60502, IEC 60332, etc.) are the basis for IS standards and are used directly in international project specifications. |
| IEC 60228 | IEC standard for conductors of insulated cables. Defines Classes 1, 2, 5, and 6. Technically equivalent to IS 8130:2013. |
| IEC 60227 | IEC standard for PVC insulated cables of rated voltages up to 450/750V. Equivalent to IS 694:2010 at the lower voltage class. H07V-U, H07V-R, H07V-K designations are defined here. |
| IEC 60502-1 | IEC standard for power cables with extruded insulation, 1kV to 30kV. NYY cable is manufactured to IEC 60502-1 at the 0.6/1kV voltage level. |
| IEC 60332 | IEC standards for flame propagation tests on cables. Part 1-2: single cable vertical flame test. Part 3-24: Category C bunched cable test (3.5L/m fill on a vertical tray). Transit and metro installations typically require Cat. C compliance. |
| NBC 2016 | National Building Code of India, 2016 edition. Part 4 (Fire and Life Safety) governs cable specification by building type and zone. Compliance established through BIS certification, not a separate NBC certificate. |
Fire Performance
FR, FR-LSH, HFFR, OI, TI — what they mean and how they are tested.
| Term | Definition |
|---|---|
| FR | Flame Retardant — the cable will not continue to burn when the ignition source is removed. Does not specify smoke density or halogen content. IS 694:2010 FR cable passes vertical flame test per IEC 60332-1-2:2004 (IS 10810 (Part 61):1988). |
| FR-LSH | Flame Retardant, Low Smoke, Halogen — FR with additional limits on smoke density and halogen acid gas emission. IS 694:2010 designation: FR-LS. OI > 29%, TI > 250°C, HCl < 15%, smoke transmittance > 60%. Different from LSZH/HFFR — the HCl limit is 15% vs 0.5%. |
| LSZH | Low Smoke Zero Halogen — alternative name for HFFR. The "zero halogen" description is colloquial — IS 17048:2018 permits HCl < 0.5%, not strictly zero. LSZH and HFFR describe the same product category. |
| HFFR | Halogen-Free Flame Retardant — the correct IS 17048:2018 designation. Made from a non-PVC compound (typically polyolefin-based) that does not contain chlorine or bromine. HCl emission < 0.5%, smoke transmittance > 60%, OI > 30%. Maximum conductor temperature 90°C is specified for HFFR insulation under IS 17048:2018 Clause 10.3 — thermoplastic LSH1-type compound, not cross-linked polyethylene (XLPE). |
| OI | Oxygen Index — the minimum oxygen concentration (as a percentage of an oxygen/nitrogen mixture) required to sustain combustion of a material. Tested per IS 10810 (Part 58):1998 / ASTM D2863. Air contains approximately 21% oxygen. A cable with OI > 21% will self-extinguish in normal air. FR-LSH requires OI > 29%. HFFR requires OI > 30%. |
| TI | Temperature Index — per IS 10810 (Part 64):2003, the temperature at which the material's Oxygen Index equals 21% (ambient-air oxygen level). Tested per IS 10810 (Part 64):2003. FR-LSH requires TI > 250°C. |
| HCl content | Hydrogen chloride acid gas emitted during combustion. Tested per IEC 60754-1. The standard limit for FR-LSH is < 15% of total gas; for HFFR < 0.5%. HCl is corrosive and toxic — damages electronic equipment and impairs lung function before reaching lethal concentrations. |
| Smoke density | Measured as light transmittance in a smoke chamber during combustion. Tested per IEC 61034-2. Cable must achieve > 60% transmittance for FR-LSH and HFFR. Standard FR PVC can fall below 20% — meaning less than one-fifth of light passes through the smoke. |
| Vertical flame test | IEC 60332-1-2:2004 (single cable): A 600mm cable specimen is held vertically and a defined flame applied for 60 seconds. The cable must self-extinguish with the charred zone not reaching the upper 50mm. Required for all IS 694:2010 and IS 17048:2018 cable. |
| Bunched cable flame test | IEC 60332-3-24:2018 Category C: Cables are installed at 3.5L/m linear density on a vertical tray. Flame applied for 20 minutes. The char must not exceed 2.5m from the burner. More demanding than the single-cable test — relevant for cable tray installations in transit and industrial environments. |
Cable Construction
Conductor, insulation, sheath, screen — the anatomy of a cable.
| Term | Definition |
|---|---|
| Conductor | The metallic core that carries current. In IS 694:2010 cable: electrolytic grade copper (99.9% purity), annealed for softness. Defined by cross-sectional area in mm² and conductor class (IS 8130:2013). |
| Cross-section area | The nominal cross-sectional area of the conductor in mm². Standard sizes: 0.5, 0.75, 1.0, 1.5, 2.5, 4, 6, 10, 16, 25, 35, 50, 70, 95, 120, 150, 185, 240, 300, 400, 500, 630mm². The area determines current carrying capacity — not the conductor diameter directly. |
| Annealed copper | Copper that has been heat-treated to remove work-hardening from the drawing process. Annealed copper is soft, flexible, and has the correct electrical resistivity specified in IS 8130:2013 / IEC 60228. All IS 694:2010 conductors use annealed copper. |
| Electrolytic grade copper | Copper of 99.9% purity, produced by electrolytic refining. Resistivity: 1.7241 × 10⁻⁸ Ω·m at 20°C. The basis for all IEC 60228 and IS 8130:2013 resistance values. |
| Insulation | The dielectric material applied over the conductor to prevent electrical conduction to adjacent conductors or earthed surfaces. In IS 694:2010: PVC compound per IS 5831:1984. In IS 17048:2018: HFFR compound (polyolefin-based). Thickness is specified by conductor size in each standard. |
| PVC | Polyvinyl Chloride — thermoplastic insulation and sheath material. Type A (IS 5831:1984): 70°C continuous rating. Flame retardant grade: IS 694:2010 FR. Low smoke grade: IS 694:2010 FR-LSH. Contains chlorine — produces HCl on combustion. |
| Sheath | The outer protective jacket of a cable assembly, applied over laid-up cores. IS 694:2010 sheath compounds: ST1 (70°C general purpose), ST2 (85°C heat-resistant), ST3 (flame retardant). For single-core non-sheathed cable (H07V-U, 6491X), there is no sheath — the conductor is insulated only. |
| Core | One insulated conductor within a multicore cable assembly. A 4-core cable contains 4 conductors, each individually insulated, laid up together inside a common sheath. |
| Lay / Lay length | The distance along the cable axis for one complete twist of a stranded conductor or multicore assembly. Shorter lay length = better flexibility and EMI rejection (for screened cable). Lay length is specified in IEC 60228 and IS 8130:2013. |
| Filler | Non-conductive material (PVC or polypropylene) used to fill the interstices between cores in a multicore cable to achieve a round cross-section and mechanical stability before sheating. |
| Screen / Shield | A conductive layer applied around a cable core or assembly to provide electrostatic or electromagnetic shielding. In IS 694:2010 screened control cable: aluminium foil with drain wire. The screen must be earthed at one end only to prevent ground loops. |
| Drain wire | A bare copper wire laid alongside or under the aluminium foil screen, providing a low-resistance earth connection for the screen. The drain wire is accessible at the cable end for single-point earthing. |
| Armour | A mechanical protection layer applied over the inner sheath, typically galvanised steel wire (SWA) or steel tape. IS 694:2010 standard cables are unarmoured. Armoured versions are project-specific and supplied only where required by the applicable installation standard. |
| Nominal OD | Overall diameter of the cable, measured over the outermost surface (sheath or insulation for unsheathed cable). Approximate — subject to manufacturing tolerance ±5%. Used for conduit sizing, cable tray loading, and gland selection. |
Electrical Parameters
Resistance, voltage drop, current rating, de-rating — the engineering numbers.
| Term | Definition |
|---|---|
| DC resistance | Resistance of the conductor measured with direct current, expressed in Ω/km at 20°C. Specified in IS 8130:2013 / IEC 60228. Used in voltage drop calculations. AC resistance is slightly higher for large conductors due to skin effect — significant above 70mm². |
| Current carrying capacity (CCC) | The maximum continuous current the cable can carry without exceeding the insulation's maximum temperature. Tabulated in IS 3961 (Part 2):2017 and BS 7671. Depends on conductor size, insulation temperature rating, installation method, ambient temperature, and grouping. |
| Voltage drop | The reduction in voltage along a cable carrying current, due to conductor resistance. Formula (single-phase): ΔV = 2 × I × L × R / 1000 volts. IS standard limit: 4% of nominal voltage. Larger conductor reduces voltage drop. |
| Voltage rating (U₀/U) | The rated voltage of a cable. U₀ = conductor to earth/screen. U = conductor to conductor. IS 694:2010: 650/1100V. IEC 60227 H07V: 450/750V. IEC 60502-1 NYY: 600/1000V. IS 694:2010 cable exceeds IEC 60227 voltage requirement. |
| De-rating factor | A correction factor applied to the tabulated current rating to account for installation conditions that differ from the reference (30°C ambient, single cable). Temperature de-rating: per IS 3961 (Part 2):2017 / BS 7671 Table 4B1. Grouping de-rating: per IEC 60364-5-52 Table B.52.17. |
| Insulation resistance | The DC resistance between conductor and earth (or between conductors), measured through the insulation. A high insulation resistance confirms insulation integrity. IS 694:2010 specifies minimum values per conductor size (typical: > 0.01 MΩ·km for 1.5mm²). Measured at 500V DC. |
| Spark test | A high-voltage test applied to cable during manufacturing — typically 5–10kV AC or DC — to detect insulation pinholes or thin spots. Conducted online during extrusion. Every metre of IS 694:2010 cable is spark-tested at the factory. |
Frequently Asked Questions
Cable terminology — common questions answered.
Quick clarifications on the most-asked-about terms in cable specification.
What is the difference between FR and FR-LSH cable?
FR (Flame Retardant) per IS 694:2010 means the cable will not continue to burn once the ignition source is removed — verified by the vertical flame test in IEC 60332-1-2:2004. FR does not specify smoke density or halogen content.
FR-LSH (Flame Retardant, Low Smoke, Halogen) — also under IS 694:2010 — adds limits on smoke and halogen acid gas: Oxygen Index > 29%, Temperature Index > 250°C, HCl < 15%, smoke transmittance > 60%. Both share the same 70°C conductor temperature rating; the differentiation is fire performance, not thermal class.
What does Class 5 conductor mean, and when must I specify it?
Class 5 per IS 8130:2013 / IEC 60228 defines a fine-stranded conductor — many thin individual wires arranged so the bundle flexes elastically. It is mandated for panel wiring and flexible applications because each strand distributes bending stress without work-hardening.
Class 1 (solid) and Class 2 (stranded) conductors are designed for fixed installation only. Using them where flexing or repeated termination disturbance occurs causes invisible work-hardening fractures at termination points — presenting as intermittent contact faults or terminal overheating, not obvious broken wires.
Why does my cable show 70°C while another shows 90°C — and which do I need?
The temperature rating is the maximum continuous conductor temperature the insulation can sustain in service. IS 694:2010 PVC cables (FR, FR-LSH, HR variants) are rated at 70°C using PVC compound per IS 5831:1984. IS 17048:2018 HFFR cables use a halogen-free thermoplastic compound rated at 90°C per Clause 10.3.
The 90°C rating affects de-rating: at higher ambient temperatures, 90°C cable retains more of its tabulated current-carrying capacity than 70°C cable. Specify per the application and applicable standard — they are not interchangeable.
What does the ISI mark with a CM/L number actually certify?
The ISI mark indicates the cable is covered by a valid BIS (Bureau of Indian Standards) manufacturing licence for the cited standard (e.g. IS 694:2010 or IS 17048:2018). The licence is issued only after BIS audits the manufacturer's production facility, quality systems, and product test samples, and is renewed periodically.
The CM/L-XXXXXXXX licence number must be printed on the cable sheath alongside the ISI mark. National Cables holds CM/L-8800140116 for IS 694:2010 and CM/L-8800227819 for IS 17048:2018 — both verifiable at bis.gov.in. An ISI mark without a printed licence number should not be accepted as proof of compliance.
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