Self-Supporting Insulated Wire (SIP): Complete Guide to Types and Applications
Self-supporting insulated wire (SIP) is a modern type of cable product for overhead power lines (OHL) and branch connections to building entrances. Its key feature is the presence of a load-bearing element that absorbs mechanical loads and insulated phase conductors, which fundamentally distinguishes it from traditional bare wires. This design provides a significantly higher level of safety, reliability, and operational advantages, leading to its widespread adoption in 0.4/0.23 kV and 10 kV distribution networks.
1. Key Advantages and Differences from Bare Wires
The transition from overhead lines (OHL) to insulated wires is a global trend in distribution power engineering. Let’s compare the key aspects:
| Criterion | Traditional Bare Wires (A, AC) | Self-Supporting Insulated Wire (SIP) | Operational and Economic Implications |
| Safety | Low. High risk of electric shock from accidental contact, short circuits due to wind-induced whipping or falling branches. | High. Insulation prevents direct contact with live parts, minimizing the risk of electric shock. Short circuits due to whipping are eliminated. | Reduction in electrical injuries to the public. Minimization of unauthorized connections (energy theft). Possibility of safe installation along building walls and within tree canopies. |
| Reliability of Power Supply | Low. Frequent outages due to wire whipping, breakage from falling trees, snow and ice accumulation. | High. Insulation and construction prevent whipping. The line is less prone to breakage. The number of accidents and outages is reduced by 60-80%. | Reduction in damages from power supply interruptions for consumers (both residential and commercial). Decrease in utility costs for emergency restoration work. |
| Operating Costs and Installation | High. Requires wide rights-of-way, tall poles, complex insulators, and hardware. Constant clearing of the route from vegetation is necessary. | Low. More compact line, allows the use of lighter and shorter poles. Simple and lightweight mounting hardware is used. Route clearing is practically unnecessary. | Reduction in construction time and costs for new OHLs. Significant decrease in maintenance costs throughout the entire lifecycle (up to 40-60%). |
| Aesthetics and Possibilities | Visually bulky lines requiring significant land allocation. | Neat appearance. Possibility of concealed installation along building facades in historical areas and dense urban environments. | Ability to modernize networks without expanding the right-of-way. Improvement of the visual appearance of populated areas. |
2. Construction and Materials
The construction of SIP varies depending on the type, but the general principles are consistent.
- Load-bearing element (neutral messenger conductor):
- In SIP-1, SIP-2, SIP-3 types, it is made of aluminum alloy (Al-Mg-Si), ensuring high mechanical strength.
- It can be insulated (SIP-2, SIP-3) or bare (SIP-1).
- It absorbs all mechanical loads (wire weight, wind, ice), allowing the use of lighter phase conductors.
- Insulated phase conductors:
- Made of aluminum (SIP-1, SIP-2, SIP-4) or aluminum alloy (SIP-3).
- Covered with insulation made of light-stabilized cross-linked polyethylene (XLPE). This material is resistant to UV radiation, ozone, temperature fluctuations, and remains flexible in cold weather.
- Insulation: Cross-linked polyethylene (denoted in the marking as “insulated”) is the standard. It ensures a long service life (over 40 years) in atmospheric conditions.
- Stranding: All elements (messenger conductor and phase conductors) are twisted into a single bundle with a specific lay length, giving the cable mechanical stability and ease of installation.
3. Main SIP Types and Their Application
The types of self-supporting insulated wires are regulated by GOST R 52373-2005 (IEC 61089) and differ in the construction of the load-bearing element and purpose.
| SIP Type | Construction and Interpretation | Purpose and Features | Rated Voltage |
| SIP-1 (and SIP-1A) | Three insulated aluminum phase conductors twisted around a bare neutral messenger conductor made of aluminum alloy. In SIP-1A, the messenger conductor is also insulated. | Main lines and branches of 0.4/0.23 kV OHLs. The most common type for rural and suburban areas. SIP-1A is safer in conditions of dense vegetation. | up to 0.6/1 kV |
| SIP-2 (and SIP-2A) | Similar to SIP-1, but all conductors, including the neutral messenger, have insulation. The insulation is designed for higher resistance to environmental influences. | 0.4/0.23 kV OHLs in marine climates, industrial atmospheres, high humidity, and saline conditions. Possesses increased corrosion resistance. | up to 0.6/1 kV |
| SIP-3 | Single-core wire. Steel-reinforced aluminum or aluminum alloy conductor (core) surrounded by cross-linked polyethylene insulation. | Main OHLs with voltages of 10-35 kV (more often 10 and 20 kV). Used for the construction and reconstruction of medium voltage distribution networks, replacing bare AC wires. | 10, 15, 20, 35 kV |
| SIP-4 and SIP-5 | Do not have a separate messenger conductor. Consist of 2, 3, or 4 identical insulated conductors made of aluminum alloy, twisted together. | Branches from OHLs to building entrances, installation along facades, street lighting installation. Installation requires a support cable or special hardware, as the wire is not truly self-supporting. | up to 0.6/1 kV |
Modern SIP types are widely represented in the catalogs of manufacturers such as JSC “Kazenergokabel”.
4. Technical Characteristics and Cross-Section Selection
The main parameters to pay attention to when choosing self-supporting protected and insulated wires:
- Rated Voltage: Specified as 0.6/1 kV for SIP-1,2,4 and 10, 20, 35 kV for SIP-3.
- Conductor Cross-Section: Standard range for SIP-1,2,4 phase conductors: 16, 25, 35, 50, 70, 95, 120, 150 mm². The cross-section of the messenger conductor is usually equal to that of the phase conductors (or larger in SIP-3).
- Number of Cores: Most often 3 phase + 1 neutral messenger (for SIP-1,2) or 1 core (for SIP-3).
- Permissible Load Current: Determined by the conductor cross-section and installation conditions (in air). For example, SIP-2 4×70 has a permissible current of about 240 A.
- Operating Temperature Range: From -60°C to +50°C for cross-linked polyethylene insulation.
- Minimum Bending Radius: Typically not less than 10 times the outer diameter of the wire.
The cross-section is selected based on calculating the maximum load of the line, considering future growth potential. For residential service entrances (15-30 kW), SIP-4 2×16 or SIP-2 4×16 is often used.
5. Hardware and Accessories for SIP Installation
Installing SIP requires special hardware, which differs from traditional OHL hardware.
- Dead-End Clamps: For securing and tensioning SIP on poles. They create a reliable mechanical grip on the messenger conductor without damaging the insulation.
- Suspension Clamps (Supports): For intermediate suspension of the wire on poles.
- Insulation Piercing Connectors (Clamps): A key element for making branch connections without stripping the insulation. Sharp contacts pierce the insulation when tightened, ensuring a reliable electrical connection and maintaining sealing.
- Pulling Grips (Stockings): Temporary tools for installation, allowing the wire to be safely tensioned with a winch.
- Connection Sleeves: For joining sections of SIP together using the compression method.
6. Features of Installation and Operation
- Tensioning: Must correspond to the design specifications. Dynamometers or calculation methods are used. Insufficient tension leads to excessive sagging, excessive tension leads to unnecessary load on the poles.
- Use of Rollers: When pulling the cable through poles, installation rollers are used to prevent damage to the insulation.
- Temperature Consideration: It is recommended to perform tensioning at a temperature close to the annual average for the given area, or with appropriate corrections.
- Descent to Building Entrance: Performed using special wall or facade brackets. The cable must be protected from mechanical damage at heights below 2.5 meters.
- Building Entry: Through sealed entry devices or pipes. It is important to prevent moisture from getting under the insulation.
7. Conclusion
Self-supporting insulated wire (SIP) is a technologically advanced and economically justified solution for modernizing and constructing distribution electrical networks. Its advantages in safety, reliability, and reduction of operating costs make it the undeniable choice for modern projects. Proper selection of the type (SIP-1 for 0.4 kV mains, SIP-3 for 10 kV lines, SIP-4 for service entrances) and cross-section, combined with high-quality mounting hardware, ensures long-lasting and uninterrupted operation of power grids for decades.
