Short Answer: The Key Property of an Outdoor Cable
The key property of a cable for open air is the combination of a UV-resistant sheath and the ability to retain elasticity at negative temperatures. An ordinary cable with a grey or white PVC sheath without UV stabilisers cracks under direct sun within 2–3 years. For outdoor use, a sheath made of light-stabilised cross-linked polyethylene, polyurethane or black PVC with carbon black filler is suitable.
For overhead power lines up to 1 kV, self-supporting insulated wires (SIP) with insulation made of light-stabilised cross-linked polyethylene are used. They are rated for operation from minus 60 °C to plus 50 °C, resistant to UV, rain and icing. For cable lines laid along building walls, trestles and open trays, cables with the “UV” index in the marking or with a black polyethylene sheath are used. For installation at negative temperatures, the minimum installation temperature is additionally checked: for SIP it is minus 20 °C, for cables in the KhL design — down to minus 30 °C.
What Influences the Cable Must Withstand
For the climate of Kazakhstan, not only frosts are dangerous. An outdoor cable is exposed to a complex of influences.
| Condition | Risk to the cable | What is required of the cable |
| Solar and UV radiation | Ageing of the sheath, cracking, exposure of conductors | UV-stabilised sheath (cross-linked polyethylene, black PVC with carbon black, polyurethane) |
| Low operating temperature | Embrittlement of insulation and sheath | Materials that retain elasticity at minus 40–60 °C |
| Low installation temperature | Destruction of insulation during installation and bending | Minimum installation temperature not higher than minus 20 °C (SIP) or minus 30 °C (KhL) |
| Rain, snow, icing | Moisture ingress into insulation, mechanical load from ice | Sealed design, resistance to atmospheric influences |
| Wind and mechanical loads | Tension, kinking, damage to the sheath | Load-bearing conductor (SIP), armour or reinforced sheath |
| Rodents | Damage to the sheath | Armour of steel tapes or wires |
The exposure to direct solar radiation over the entire service life must not exceed 2000 h for cables without a special “UV” design. Cables in the “UV” design may be laid in open air without protection from direct solar radiation. UV resistance is confirmed by tests according to GOST 20.57.406-81 (method 211-1).
Which Design Provides Protection
Protection from open-air influences is provided by the sheath and insulation materials, as well as structural elements.
Insulation. For outdoor cables, insulation made of cross-linked polyethylene (XLPE), light-stabilised cross-linked polyethylene or ethylene propylene rubber (EPR) is used. These materials retain dielectric properties and flexibility at negative temperatures and do not break down under UV. Ordinary PVC compound for insulation becomes brittle at minus 30 °C.
Sheath. For the outer sheath of outdoor cables, light-stabilised black cross-linked polyethylene, polyurethane, black PVC with carbon black filler or rubber compounds based on isoprene rubber are used. The black colour provides UV protection, since carbon black absorbs ultraviolet. Light-coloured PVC without UV stabilisers is not suitable for open installation. NYY-J cable with a black PVC sheath is resistant to UV rays and is used outdoors.
Armour. Steel tapes or galvanised wires protect the cable from mechanical damage and rodents. For installation in the ground without a pipe, armour is mandatory. For overhead suspension, armour is not required if the cable has a load-bearing element.
Hydrophobic filling. Filling the spaces between conductors with a hydrophobic compound prevents the spread of moisture along the cable when the sheath is damaged. For cables operating under conditions of temperature and humidity fluctuations, this is an important element.
If the cable must not propagate combustion or must maintain operability during a fire, the indices ng, LS, HF or FR are added to the outdoor design. Combinations of these properties are analysed in the materials: table of differences between LS, HF, LSLTx, FRLS and FRHF and fire-resistant and non-flame propagating cable.
How to Choose a Suitable Cable
The selection algorithm is built from the operating conditions to the specific design.
- Determine the line type. Overhead power line up to 1 kV — SIP is used. Cable line along walls, trestles, open trays — a cable with a UV-resistant sheath is used.
- Determine the operating temperature range. For Kazakhstan, winter temperatures reach minus 40–45 °C in the northern and central regions. SIP is rated for minus 60 °C, cables with a black polyethylene sheath — for minus 40–60 °C depending on the design.
- Determine the minimum installation temperature. SIP permits installation at a temperature not lower than minus 20 °C. Cables in the KhL design — down to minus 30 °C. At a lower temperature, pre-heating is required.
- Check the UV resistance of the sheath. For open installation, the sheath must be light-stabilised. Cables with the “UV” index in the marking have passed tests for resistance to solar radiation. SIP has insulation made of light-stabilised cross-linked polyethylene.
- Take mechanical loads into account. For overhead lines, SIP has a load-bearing conductor made of aluminium alloy. For cable lines on open sites, armoured cables or cables with a reinforced sheath are used.
- Check the fire characteristics. If the cable is laid in buildings or at facilities with fire safety requirements, the indices ng, LS or FR are added. The properties of smoke formation and toxicity of combustion products are checked separately: smoke, halogens and toxicity of a cable.
For overhead lines up to 1 kV, the choice between SIP and a bare conductor is determined by the requirements for reliability and safety. The comparison is given in the material: SIP or bare conductor: what to choose for an overhead line. The rules for laying SIP and installation norms are described in the article laying of self-supporting insulated wire.
Where It Is Applied
Overhead power lines up to 1 kV. Branches from overhead lines to building entries, installation along building walls and engineering structures. SIP-2 and SIP-4 with insulation made of light-stabilised cross-linked polyethylene are used.
Outdoor routes along walls and trestles. Cables laid along building facades, open trays and trestles are exposed to UV radiation and precipitation. Cables with a black polyethylene sheath or in the “UV” design are used.
Industrial facilities and oil and gas sites. On open sites of Kazakhstan’s fields, cables operate at temperatures down to minus 40 °C and below. Cables in the KhL design with a rubber or polyethylene sheath, armoured to protect against mechanical damage, are used.
Construction sites and mobile mechanisms. KG-KhL cables and similar ones are used to power mobile equipment. They retain flexibility at minus 60 °C and are resistant to UV.
Lighting and heating of open sites. For powering outdoor lighting, heating systems and other outdoor equipment, cables with a UV-resistant sheath and moisture protection are used. The choice between copper and aluminium conductors affects the permissible current and voltage drop. The design and characteristics of a power cable are described in a separate material: power cable: design, types, characteristics.
Typical Mistakes
Using VVG or VVGng cable for open installation without protection. A grey or white PVC sheath without UV stabilisers cracks under direct sun within 2–3 years. For open installation, a cable with a black UV-resistant sheath or protection in the form of a pipe, corrugated conduit or duct is required.
Assuming that any cold-resistant cable is suitable for installation in severe frost. Operating temperature and installation temperature are different parameters. SIP operates at minus 60 °C, but installation without heating is permitted only down to minus 20 °C. Installation at a lower temperature leads to cracking of the insulation.
Ignoring UV resistance when choosing a cable for an overhead line. A cable intended for underground installation may not have UV stabilisation. During open installation, the sheath breaks down under the influence of solar radiation. For overhead lines, SIP with light-stabilised cross-linked polyethylene is used.
Confusing the KhL and EKhL designs. KhL is rated for installation down to minus 30 °C, EKhL — down to minus 40 °C. For conditions where installation is carried out at minus 35 °C, KhL is not suitable; EKhL or pre-heating is required.
Choosing a cable only by the designation without checking the documentation. Different manufacturers use different materials and indicate different temperature ranges for the same climatic design. The specific values are checked against the technical specifications and the cable passport.
FAQ
Which cable can be laid outdoors without protection?
Without protection from direct solar radiation, cables in the “UV” design, SIP with insulation made of light-stabilised cross-linked polyethylene, as well as cables with a black polyethylene or polyurethane sheath can be laid. Cables with a grey or white PVC sheath without UV stabilisers require protection in the form of a pipe, corrugated conduit or duct.
At what temperature can SIP be installed?
The minimum installation temperature for SIP-2 and SIP-4 is minus 20 °C. At a lower temperature, installation without pre-heating is not permitted. The operating temperature of SIP is from minus 60 °C to plus 50 °C.
What is the difference between operating temperature and installation temperature?
Operating temperature is the range in which the cable can operate after installation, when the insulation is no longer deformed and the current heats the conductor. Installation temperature is the temperature at which the cable can be bent and laid while the insulation retains plasticity. These parameters differ: SIP is operated at minus 60 °C but installed at a temperature not lower than minus 20 °C.
What to do if a cable needs to be laid at a temperature below the permissible one?
Pre-heating of the cable to a temperature not lower than the permissible one for installation is applied. Heating is carried out in a heated room or using special equipment. An alternative is to use a cable in the EKhL design, if its minimum installation temperature corresponds to the conditions.
How to check that a cable is UV-resistant?
UV resistance is confirmed by tests according to GOST 20.57.406-81 (method 211-1). Cables in the “UV” design have the corresponding index in the marking. For SIP, UV resistance is provided by insulation made of light-stabilised cross-linked polyethylene. The specific data are checked against the technical specifications and the cable passport.
Sources
- GOST 15150-69 “Machines, instruments and other technical products. Versions for different climatic regions. Categories, operating, storage and transportation conditions as to the influence of climatic factors of the environment” — in force — official text on meganorm.ru — classification of climatic designs, including KhL and UHL.
- GOST 31946-2012 “Self-supporting insulated and protected wires for overhead power lines” — in force — official text on meganorm.ru — requirements for SIP, temperature ranges, UV resistance.
- GOST 20.57.406-81 “Comprehensive quality control system. Electronic, quantum electronic and electrical products. Test methods” — in force — method 211-1 “Test for resistance to solar radiation”.
- GOST R 50571.5.52-2011/IEC 60364-5-52:2009 “Low-voltage electrical installations. Part 5-52. Selection and erection of electrical equipment. Wiring systems” — in force — official text — requirements for protecting cables from UV radiation, conditions for open-air installation.
- GOST 31996-2012 “Power cables with plastic insulation for rated voltages of 0.66; 1 and 3 kV” — in force — official text of the standard — requirements for the design of power cables, climatic designs.
- Electrical Installation Code of the Republic of Kazakhstan 2015, as amended by the order of the Minister of Energy of the Republic of Kazakhstan dated 31.10.2022 No. 340 — in force — IPS “Adilet”, adilet.zan.kz — requirements for cable installation under various conditions, use of SIP on overhead lines.
- Technical specifications for KG-KhL, SIP-2, SIP-4 cables — in force — manufacturers’ technical documentation — temperature ranges of operation and installation, UV resistance.
