Installation of overhead power lines using self-supporting insulated wire (SIP) is a standard in modern construction and modernization of electrical networks. Correct stretching technology ensures line durability, operational safety and prevents emergency breaks in winter. Unlike old bare wires, SIP has a specific design that requires a special approach to creating traction force.
The process of laying a line is not just the physical movement of a cable from support to support, but a strictly regulated operation, where each stage affects the final result. Errors at stage stretches can lead to uneven sagging, damage to the insulation, or even failure of the reinforcement under load. That is why the question of how to correctly pull SIP requires a detailed consideration of all the nuances, from the choice of equipment to the final adjustment.
In this article we will analyze the professional algorithm of actions that electrical installation crews use. You will learn about the role leader cable, features of use tension winches and ways to control the tension force. Understanding these processes is necessary for both specialists and customers who want to control the quality of work performed.
Preparatory stage and selection of equipment
Before starting work, it is necessary to conduct a thorough inspection of the route and prepare all the necessary tools. The quality of installation directly depends on how well the mounting equipment. The use of unsuitable clamps or winches can damage the cable cores during installation.
Particular attention should be paid to the choice traction rope. For light grades of SIP (for example, SIP-4), durable synthetic rope is often used, which is lighter and does not conduct current. However, for heavy four-wire lines with a supporting zero core (SIP-1, SIP-2), it is recommended to use a steel leader cable with a diameter of at least 6 mm.
- 🛠️ Tension winch - a manual or motorized mechanism that creates the necessary force.
- 🔗 Tension clamps - wedge or chain type for capturing the leader cable.
- 📏 Dynamometer — a device for precise control of tension force (critically important).
It is important to check the condition of the supports and the fittings installed on them before starting work. Brackets, anchor clamps and insulators must be securely fastened and withstand the design loads. Any defects at the preparation stage can cause a tension accident.
⚠️ Attention: It is strictly forbidden to attach the tensioning mechanism directly to insulated SIP conductors without using a special leader cable. This will lead to deformation of the cores and disruption of the insulation tightness.
Laying the leader cable and rolling out the cable
The first stage of direct installation is laying leader cable along the entire length of the route. This auxiliary cable is pulled through blocks mounted on supports and serves as the basis for the subsequent pulling of the main cable. Rolling can be done manually or using specialized rolling carts.
When rolling out, SIP coils should unwind freely, without twisting or dragging along the ground. Damage to the outer shell contact with stones, asphalt or vegetation is unacceptable, as this will reduce the service life of the line. If the route passes through a forest or overgrown area, it is recommended to first clear the clearing.
☑️ Control of SIP rolling
The leader cable is attached to the SIP through a special swivel, which prevents the cable from twisting around its axis during traction. The connection must be made using a tension clamp, which evenly distributes the force onto the supporting zero core (in the case of SIP-1/2) or over the entire bundle (for SIP-4).
The pulling speed should be kept to a minimum so that operators can control how the cable passes through the blocks on each support. Sudden jerks can cause the wires to overlap or the cable to jump off the rollers, which will require stopping and re-adjusting the section.
Tension technology and force control
The most crucial moment is the immediate SIP stretch. The tensile force must strictly correspond to the design data, which depends on the type of wire, span (distance between supports) and climatic conditions of the region. Insufficient tension will lead to too much sagging, and excessive tension will lead to overloading of the supports and breakage when the temperature drops.
To control the force, a dynamometer is used, installed between the winch and the cable. The device readings are checked against installation tables for a specific air temperature.
Why can’t you pull it “by eye”?
Visual assessment of tension often leads to errors. Aluminum conductors have a high coefficient of linear expansion, and an error of a few millimeters of sag in summer can result in a break in winter at temperatures as low as -40°C.
The tensioning process is carried out smoothly, without jerking. After achieving the required force, the cable is temporarily fixed to the anchor support. Only after this can the tension mechanism be loosened and proceed to the installation of branches or installation of intermediate clamps.
Below is a table of approximate tension forces for common brands of SIP (data may vary depending on the manufacturer and span length):
| Brand SIP | Diameter (mm) | Max. force (kN) | Support type |
|---|---|---|---|
| SIP-1 3x16+25 | 15-17 | 1.2 - 1.5 | Intermediate |
| SIP-2 3x50+70 | 22-24 | 3.0 - 3.5 | Anchor |
| SIP-4 2x16 | 14-16 | 1.0 - 1.2 | Intermediate |
| SIP-2 3x95+95 | 28-30 | 5.5 - 6.0 | Anchor |
Key point: The tension is always carried out to the design value indicated in the installation tables for the current air temperature, and not “all the way” or “so as not to sag”.
Fastening and fixing on supports
After completing the tension and checking the sag, the cable is finally attached to the supports. On anchor supports (corner, end) SIP is fixed in anchor clamps, which transmit the tension force to the support body. The design of the clamp must correspond to the type of cable (with a supporting zero core or self-supporting).
At intermediate supports, where the cable does not experience longitudinal tension, support clamps or ties are used. Here it is important to ensure free movement of the wire in the clamp during temperature fluctuations in order to avoid breaking the wires. Supporting reinforcement often has a hinged connection to compensate for wind loads.
- 🔒 Anchoring - rigid fixation that absorbs tension force.
- 🔄 Support — fixation that allows the cable to move in the longitudinal direction.
- ⚡ Separator - a device for separating phase conductors after an anchor span.
When fastening, it is necessary to monitor the bend radius of the cable. For SIP, the minimum bending radius is 10 outer diameters of the cable. Violation of this rule will result in permanent damage to the insulation and possible short circuit in the future.
⚠️ Attention: When installing on concrete supports, use only certified reinforcement with anti-corrosion coating. Contact of aluminum elements with concrete or steel without insulation will cause rapid galvanic corrosion.
Sagging standards and line dimensions
Controlling sag (sag) is a critical safety parameter. Regulatory sag is calculated in such a way that during the hottest period or at maximum current load the wire does not fall below the permissible size. For lines with voltages up to 1 kV, the minimum distance to the ground must be at least 6 meters above the roadway and 5 meters above pedestrian areas.
When installing in winter, tension is carried out taking into account temperature compression. If you pull the wire tight in winter, in summer it will sag to a dangerous level. Conversely, weak tension in winter can lead to breakage in severe frost and ice formation. Mounting tables take these factors into account and are a mandatory document for the electrician.
It is also necessary to take into account the distance to nearby buildings, trees and other utilities. Wind load can significantly increase the amplitude of wire vibrations, so (margin) distance is required.
Visual inspection of sag is often carried out by eye using a rod with marks or an optical device. Experienced installers can determine critical sagging by the nature of wire vibrations, but instrumental control is always preferable.
Typical mistakes when installing SIP
Failure to comply with installation technology often leads to premature failure of the line. One of the most common mistakes is to use uncalibrated instrument or homemade tensioning devices. This makes it impossible to accurately control the force, which is a serious violation.
Another common mistake is dragging the cable on the ground or snow. Even if external insulation cross-linked polyethylene It seems durable, microcracks and abrasions become foci for the development of electrical breakdown under the influence of ultraviolet radiation and moisture.
- ❌ Twisting tow during rolling, leading to uneven load distribution.
- ❌ Ignoring the swivel, which causes the cable to twist and damage the insulation.
- ❌ Stretch by eye without taking into account temperature and span length.
Errors also include incorrect selection of the point of application of traction force. You should always pull on the supporting neutral core (in systems with it) or evenly on the entire harness through special stockings. Pull on phase conductors is unacceptable.
Pro tip: Use talcs (hand winches) with a ratchet mechanism that has a safety factor of at least 2 tons. This will ensure smooth operation and the ability to accurately adjust tension without jerking.
FAQ: Frequently asked questions
Is it possible to pull SIP manually without a winch?
For short spans (up to 25-30 meters) and light grades of cable (SIP-4 2x16), manual tensioning by a team of 3-4 people is possible. However, for standard spans of 40-50 meters or more, the use of a mechanical winch is mandatory to ensure uniform force and safety.
Do I need to remove insulation to secure it in the clamp?
No, the vast majority of modern SIP fittings (anchor and support) are designed for installation without stripping the insulation. The insulation is punctured by special teeth inside the clamp, ensuring reliable contact and tightness. The core needs to be stripped only for connection to insulator pins or equipment.
What is the minimum distance from the SIP to the building window?
According to the PUE (Electrical Installation Rules), the distance from the SIP wire to windows and balconies must be at least 1.5 meters in the horizontal plane. This ensures the safety of residents and the ability to ventilate the premises.
What to do if the insulation is damaged during stretching?
Installation must be stopped immediately. The damaged area is cut out and the connection is made using sealed connection sleeves with an insulating heat-shrinkable sleeve. Operation of a line with damaged insulation is prohibited.