Overview
IEC 60055-2:1981/AMD2:2005 is an essential international amendment issued by the International Electrotechnical Commission (IEC) concerning paper-insulated metal-sheathed cables (PILC) with rated voltages up to 18/30 kV. This amendment specifically addresses the general and construction requirements for these cables, which have copper or aluminium conductors and exclude gas-pressure and oil-filled cable types. The document elaborates on updated operating temperatures, construction specifications, installation methods, and continuous current ratings for these cables, making it a critical resource for electrical engineers and cable manufacturers aiming to maintain compliance with international standards.
Key Topics
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General Construction Requirements
Defines the model cable constructions and dimensions for single-core and three-core PILC cables, including assumptions on armour type and oversheath materials such as PVC.
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Maximum Operating Temperatures
Specifies permissible conductor temperatures for these cables installed predominantly in horizontal positions and outlines how these relate to steady-state continuous current ratings.
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Continuous Current Ratings (Appendix C)
Provides tabulated steady-state current ratings calculated according to IEC 60287 methods, covering varied cable types:
- Single-core cables (3.6/6 kV to 18/30 kV)
- Three-core belted cables (3.6/6 kV and 6/10 kV)
- Three-core radial field cables (8.7/15 kV to 18/30 kV)
- Individually lead-sheathed three-core cables (12/20 kV and 18/30 kV)
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Installation Conditions and Methods
Details current rating calculations for different installation scenarios including:
- Single-core cables in air on brackets or ladders (trefoil and horizontal formations)
- Direct burial in soil at 0.8 m depth
- Cables installed inside earthenware ducts
- Three-core cable configurations in air, direct burial, and ducts
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Soil Thermal Resistivity and Environmental Considerations
Assumes thermal resistivity of soil at 1.5 K·m/W for buried cables; includes correction factors for varying soil conditions and ambient temperatures, emphasizing the need to refer to IEC 60287 for more complex environmental factors like solar radiation.
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Sheath Bonding Practices
Assumes solid bonding (earth grounding) of cable sheaths at both ends without transposition, with notes on the impact of alternative bonding techniques-such as single-point bonding or cross-bonding-on circulating currents and cable ratings.
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Load and Grouping Factors
Relates current ratings to balanced three-phase 50 Hz systems and provides guidance on derating factors when multiple cables or circuits are installed in close proximity.
Applications
IEC 60055-2:1981/AMD2:2005 applies to electrical utilities, cable manufacturers, and engineers involved in medium voltage power distribution networks requiring reliable and standardized paper-insulated metal-sheathed cables. Typical applications include:
- Underground and overhead power transmission in urban and industrial environments.
- Power cable installations within ducts, direct burial in soil, or aerial setups.
- Design and specification of high-performance copper or aluminium conductor cables for distribution systems up to 18/30 kV.
- Selection of cables compliant with international safety, operating temperature, and current rating standards to ensure efficiency and longevity in power systems.
- Evaluations involving soil thermal properties and installation methods for optimal current carrying capacity.
These practical applications of the standard improve system reliability, prevent overheating, and ensure safety compliance in complex electrical infrastructure projects.
Related Standards
- IEC 60287 – Electric cables - Calculation of the current rating - Fundamental methods and applications, including thermal and electrical parameters.
- IEC 60287-2-1 – Part 2-1 of IEC 60287, covering thermal resistance calculations.
- IEC 60287-3-1 – Part 3-1 addressing operating conditions and cable selection.
- IEC 60853 – Calculation of cyclic ratings for cables subjected to varying loads.
- IEC 60986 – Defines temperature limits under short-circuit conditions for cables with rated voltages from 6 kV to 30 kV.
These complementary standards provide comprehensive methodologies and data essential for accurate cable rating, installation design, and safe operation.
Keywords: IEC 60055-2, paper-insulated metal-sheathed cables, PILC, rated voltage 18/30 kV, cable construction, current rating, cable installation methods, cable standards, cable temperature limits, electrical power distribution cables
Open preview (PDF)Amendment 2 - Paper-insulated metal-sheathed cables for rated voltages up to 18/30 kV (with copper or aluminium conductors and excluding gas-pressure and oil-filled cables) - Part 2: General and construction requirements
