Laying Control Cables: Complete Guide to Installation and PUE Regulations
Laying control cables is a crucial stage in the creation of automation, dispatching, and power supply systems for control circuits. Control cables, unlike power cables, are designed to transmit control signals, measure parameters, and power secondary circuits. The reliability of expensive equipment, noise immunity of signals, and operational safety depend on how competently their installation is carried out. Installation errors can lead to false triggering of automation, failure of electronic components, and difficulties during maintenance.
In this guide, we will thoroughly analyze the main methods of laying control cables: in trays, trenches, along walls and structures. We will consider the key requirements for laying control cables according to the PUE (Electrical Installation Code), the specifics of joint laying of power and control cables, rules for underground installation, and provide practical recommendations based on regulatory documents and professional experience.
1. Main Methods of Laying Control Cables
The choice of installation method is determined by the route conditions, cable type, requirements for protection against interference and mechanical damage, as well as economic feasibility. Let’s consider the most common methods.
1.1. Laying Control Cables in Trays
Laying control cables in trays is the most common method at industrial facilities, in buildings, and cable structures. Trays provide convenient access, good cooling, and the possibility of quick replacement or addition of cables.
- Types of trays:
- Perforated — lightweight, with good ventilation.
- Non-perforated (solid) — for protection against dust and moisture, can be used as screens.
- Ladder type — for large diameter cables and heavy routes.
- Wire mesh — light and flexible, convenient for installation.
- Rules for laying in trays:
- Cables are laid in rows or bundles; multi-layer laying is allowed with a corresponding reduction in current loads.
- The distance between cables in a row and between rows should ensure their cooling and the possibility of installing couplings.
- Fastening is done with bands (cable ties) at a pitch that prevents sagging. For fire-resistant lines, metal fasteners are used.
- On vertical sections, cables are secured against slipping.
1.2. Laying Control Cables in a Trench
Laying control cables in a trench is used for external networks when overhead installation is impossible or impractical. It requires strict adherence to rules for protection against mechanical damage, moisture, and chemical influences.
- Basic rules for underground laying:
- Cable type: For direct burial in the ground, armored control cables (e.g., KVBbShv, AKVBbShv) or cables with a reinforced sheath must be used. Unarmored cables are only allowed to be laid in pipes.
- Trench depth: At least 0.7 m to the top of the cable, at least 1 m when crossing a roadway.
- Bedding: A cushion of sifted sand at least 10 cm thick is placed at the bottom of the trench.
- Protection: The cable is covered with a layer of sand from above, then a layer of earth. For protection against digging, a warning tape or a layer of bricks is laid.
- Distances: When laying several cables in one trench, the distance between them must be at least 100 mm for cables up to 10 kV and 250 mm for communication cables.
1.3. Laying Along Walls and Building Structures
- Surface mounting: The cable is attached directly to walls, columns, trusses using brackets, clips, or on cables. Used in industrial premises, on overpasses.
- Laying in boxes and cable ducts: An aesthetic method for office and administrative buildings, providing protection against mechanical damage and easy access.
- Concealed installation: In wall chases or floor screeds (in pipes). Requires preliminary planning and complicates repairs.
1.4. Laying in Cable Structures (collectors, tunnels, channels)
Used when there is a large number of cables. Cables are laid on cable structures (brackets, shelves) with standardized distances. Convenient access for maintenance and repair is ensured.
2. Joint Laying of Power and Control Cables
Joint laying of power and control cables is a common task requiring special attention due to possible electromagnetic influences of power lines on control and measurement circuits.
2.1. Basic Rules for Separating Routes
- Minimum distances: According to PUE (clauses 2.3.86-2.3.88), the clear distance between power cables up to 1 kV and control cables should generally be at least 100 mm. When laying in parallel over long sections, this distance may be increased.
- Shielding: To protect control circuits from interference, it is recommended to use shielded control cables (e.g., KVVGE), as well as to lay power and control cables on opposite sides of passages or in different trays with dividing partitions.
- Crossings: When crossing power and control cables, the angle should be 90° (right angle), and the distance at the crossing point should be at least 250 mm for cables up to 35 kV.
- Strictly prohibited: Joint laying of power and control cables in the same pipe, the same box, or closely together without separation, especially for circuits with high currents and circuits with microelectronic components.
2.2. Joint Laying of Control Cables of Different Circuits
- Cables for measurement, control, signaling, and communication circuits are generally allowed to be laid together.
- Circuits with different voltage and frequency levels (e.g., 220V AC and 24V DC) are recommended to be laid separately or using screens.
- For automation system cables sensitive to interference, special shielded and twisted pairs are used.
3. Laying Control Cables: PUE Requirements and Regulatory Framework
Laying control cables PUE is mainly regulated by section 2.3 “Cable lines with voltage up to 220 kV”. Here are the key requirements.
| Parameter | PUE and Regulatory Document Requirement |
|---|---|
| Cable selection by insulation | For control cables laid in premises, channels, tunnels, cables with polyvinyl chloride (PVC) or polyethylene insulation in a PVC or polyethylene sheath are generally used (e.g., KVVGng-LS). For aggressive environments and laying in the ground — armored (KVBbShv). |
| Bending radii | The minimum bending radii for control cables must comply with GOST and technical data sheets. Usually, for unarmored cables — at least 6 outer diameters, for armored cables — at least 10 diameters. These rules for laying control cables are mandatory to preserve the integrity of the cores and insulation. |
| Cable fastening | Cables must be secured against displacement and sagging. The fastening pitch on horizontal straight sections is determined by the project, but is usually 0.5-1 m for horizontal and 1-2 m for vertical routes. Fastening is reinforced at bends, near couplings, and entries. |
| Installation temperature conditions | Laying cables without preheating is allowed at temperatures not lower than: -15°C for unarmored cables in PVC sheath, -7°C for armored cables. At lower temperatures, warming up is required. |
| Protection against mechanical damage | In places where mechanical damage is possible, cables must be protected by boxes, pipes, or guards. When crossing driveways and passages, installation is carried out in pipes. |
| Fire safety | For group laying in premises, tunnels, collectors, cables that do not propagate combustion (with the “ng” index) must be used, and for critical facilities — with low smoke and gas emission (LS) and halogen-free (HF). |
4. Choosing a Control Cable Depending on Laying Conditions
The correct choice of cable brand is the foundation of the entire line’s reliability. Here are selection recommendations.
- For laying inside dry and wet rooms (in trays, along walls):
- Optimal choice: control cable LS of grades KVVGng(А)-LS or KVVGEng(А)-LS (shielded). They do not propagate combustion and emit little smoke, which is safe for people.
- For systems sensitive to interference — shielded versions (KVVGE).
- For laying in the ground (trenches):
- Armored cables are required: KVBbShv, KVKbShv, AKVBbShv. The armor protects against rodents and accidental damage.
- For aggressive soils — cables with a protective hose made of polyethylene (Shp).
- For laying in places with high fire safety requirements:
- Cables with the index ng(А)-FRLS (fire-resistant) — for fire protection systems.
- Cables with the index ng(А)-LSLTx (low toxicity) — for children’s and medical institutions.
- For laying outdoors (overpasses, facades):
- Cables with a sheath resistant to UV radiation (usually black polyethylene or special grades of PVC).
5. Main Errors When Laying Control Cables
- Ignoring the separation of power and control circuits: Leads to false triggering and malfunctions in automation operation.
- Laying unarmored cable in the ground without pipes: Guarantees rapid damage by rodents or corrosion.
- Non-compliance with bending radii: Internal damage to cores and insulation is not visible visually but leads to failures.
- Lack of length reserve (compensation): During temperature expansion or movement of structures, the cable experiences tension.
- Dense packing of a large number of cables in trays without ventilation: Can lead to overheating, especially for power circuits.
- Incorrect fastening: Using plastic ties for fire-resistant lines, too tight fastening deforming the cable.
- Lack of marking: Hinders installation, maintenance, and fault finding.
6. Conclusion
Competent laying of control cables is a complex task requiring consideration of many factors: from choosing the optimal installation method (in trays, trenches, along walls) to strict compliance with the requirements for laying control cables of the PUE. Special attention should be paid to the joint laying of power and control cables to ensure noise immunity of control circuits. Only an integrated approach, including the correct choice of cable brands (e.g., KVVGng for indoor installation or armored versions for ground), adherence to installation technology, and the use of high-quality materials, guarantees reliable and long-lasting operation of automation and control systems.
The range of cable and wire products from JSC “Kazenergokabel” includes a full range of control cables with copper and aluminum conductors, in various designs: unarmored (KVVG, KVVGE) for premises, armored (KVBbShv) for laying in the ground, with “ng-LS” indices for fire safety during group laying, as well as fire-resistant “FR” versions for fire protection systems. All products are certified and comply with GOST and TR CU requirements, guaranteeing the reliability and durability of your cable lines.
