Control Cable Laying: Methods, PUE Regulations and Practical Recommendations
Laying of control cables is a critical stage in the construction of automation, dispatch, signaling and control systems. Control cables are intended for transmitting control signals, measuring parameters and supplying secondary circuits. The reliability of expensive equipment, the immunity of signals to interference and the safety of operation depend on how competently the laying is performed. Installation errors can lead to false tripping of automation, failure of electronic components and difficulties during maintenance.
In this guide we will examine in detail the main methods of laying control cables: in trays, pipes, trenches, as well as the specifics of joint laying with other cable lines. We will consider the key requirements for laying control cables according to the PUE, the 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 laying method is determined by the route conditions, the type of cable, requirements for protection against interference and mechanical damage, as well as economic feasibility.
1.1. Laying control cables in trays
Laying control cables in trays is the most common method in industrial facilities, buildings and cable structures. Trays provide convenient access, good cooling and the ability to quickly replace or add cables.
- Types of trays: perforated (lightweight, with good ventilation), non‑perforated (for protection against dust and moisture), ladder type (for large‑diameter cables), wire (light and flexible).
- Rules for laying in trays:
- Cables are laid in rows or bundles; multi‑layer laying is permitted provided current loads are derated accordingly.
- The distance between cables in a row and between rows must ensure adequate cooling and space for installing joints.
- Cables are secured with straps (cable ties) at intervals that prevent sagging. For fire‑rated lines, metal fasteners are used.
- On vertical sections, cables must be secured against slipping.
1.2. Laying control cables in pipes
Laying control cables in pipes is used for protection against mechanical damage, aggressive environments, stray currents, as well as when crossing roads, driveways and where additional insulation is required.
- Types of pipes:
- Polyethylene pipes (HDPE, LDPE): the most common. Lightweight, flexible, corrosion‑resistant, with a low coefficient of friction.
- Asbestos‑cement pipes: strong, non‑combustible, but heavy and brittle. Require a concrete foundation.
- Steel pipes: used on short sections with high mechanical loads (under railways, highways) as well as in fire‑hazardous areas. Require anti‑corrosion protection.
- Laying technology in pipes:
- Pipes are laid on a prepared base (sand bed, concrete screed).
- Special lubricants are used to facilitate cable pulling, and manholes are installed at route turns.
- After the cable is pulled, the free space in the pipe is sealed to prevent moisture ingress and rodents.
- When several cables are laid in a single pipe block, the distance between pipes must be at least 100 mm to ensure heat dissipation.
1.3. Laying control cables in a trench and in the ground
Laying control cables in a trench is used for outdoor networks when overhead installation is not possible or practical. Laying control cables in the ground requires strict adherence to rules to protect against mechanical damage, moisture and chemical influences.
- Cable type: For direct burial in the ground, armored control cables (KVBbShv, AKVBbShv) or cables with reinforced sheath must be used. Unarmored cables may only be laid in pipes.
- Trench depth: At least 0.7 m to the top of the cable; at road crossings, at least 1 m.
- Bedding: A bed of screened sand at least 10 cm thick is placed on the trench bottom.
- Protection: Above the cable, a layer of sand (10 cm) is placed, then a layer of soil. To protect against excavation, a warning tape or a layer of brick is laid.
- Distances: When laying multiple cables in one trench, the distance between them must be at least 100 mm for cables up to 10 kV.
2. Joint laying of control cables
Joint laying of control cables with power lines, as well as with each other, requires special attention due to possible electromagnetic interference and thermal effects.
2.1. Joint laying with power cables
- In a trench: The distance between a control cable and a power cable with voltage up to 10 kV must be at least 100 mm; for voltage 20–35 kV, at least 250 mm.
- In cable structures (trays, collectors): Control cables should preferably be laid below power cables to reduce heating from upward heat flows. Laying above power cables is allowed provided a vertical distance of at least 200 mm is maintained.
- On cable racks: When no separating partition is present, the distance between a power cable and a control cable on adjacent shelves must be at least 200 mm. If a solid metal partition is installed, the distance may be reduced to 50–100 mm.
- In a single pipe: Joint laying of power and control cables in the same pipe is generally not permitted. Separate pipes (ducts) within a block are used for control cables.
2.2. Joint laying of control cables among themselves
- In cable structures, control cables may be laid in bundles and in multiple layers. Control cables laid in this way must have sheaths of the same type, and the bundle diameter should not exceed 100 mm.
- When cables of different circuits (e.g., signaling and automation) are laid together, possible mutual interference must be considered. For sensitive circuits, shielded cables (KVVGE) are recommended.
- Circuits with different voltage levels (e.g., 220V AC and 24V DC) should preferably be laid separately or with shielding applied.
3. Control cable laying according to PUE: key requirements
Control cable laying according to PUE is primarily governed by section 2.3 “Cable lines with voltage up to 220 kV”. The following are the key requirements applicable to control cables.
| Parameter | PUE and regulatory requirement |
|---|---|
| Cable insulation selection | For control cables laid indoors, in channels, tunnels, cables with PVC or polyethylene insulation and PVC or polyethylene sheath are used. For aggressive environments and underground installation — armored (KVBbShv). |
| Bending radii | Minimum bending radii for control cables: for unarmored — at least 6 outer diameters, for armored — at least 10 outer diameters. |
| Cable fixing | Cables must be secured against displacement and sagging. Fixing spacing on horizontal straight sections is typically 0.5–1 m, on vertical sections — 1–2 m. At bends, near joints and entry points, fixing is reinforced. |
| Installation temperature conditions | Laying without preheating is permitted at temperatures not lower than: -15°C for unarmored cables with PVC sheath, -7°C for armored cables. At lower temperatures, preheating is required. |
| Protection against mechanical damage | In places where mechanical damage is possible, cables must be protected by trays, pipes or barriers. When crossing driveways and passageways, laying is carried out in pipes. |
| Fire safety | For group laying in rooms, tunnels, collectors, cables that do not propagate flame (with “ng” index) must be used; for critical facilities — with low smoke and gas emission (LS). |
4. Selection of control cables depending on laying conditions
Proper selection of the cable brand is the foundation of the entire line’s reliability. Recommendations for selecting control cables:
| Laying conditions | Recommended cable brands | Features |
|---|---|---|
| Inside dry and wet areas (trays, along walls) | KVVG, KVVGE (shielded), KVVGng‑LS | Flame retardant; shielded versions for sensitive circuits. |
| In ground (trenches) | KVBbShv, AKVBbShv, KVKbShv | Armored cables, protection against rodents and mechanical damage. |
| In pipes and blocks | AKVVG, KVVG, KVVGE | Unarmored, with PVC or polyethylene insulation. |
| In areas with high fire safety requirements | KVVGng(A)-LS, KVVGng(A)-FRLS | Fire‑resistant, with reduced smoke and gas emission. |
| Outdoor (trestles, facades) | Cables with sheath resistant to UV radiation (black polyethylene or special PVC compounds) | Protection against solar radiation and atmospheric influences. |
5. Common mistakes when laying control cables
- Ignoring separation of power and control circuits: leads to false tripping and malfunction of automation.
- Laying unarmored cable directly in ground without pipes: virtually guarantees rapid damage by rodents or corrosion.
- Failure to observe bending radii: internal damage to conductors and insulation is not visible visually but leads to failures.
- No length reserve (compensation): cables experience tension due to thermal expansion or structural movements.
- Dense packing of many cables in trays without ventilation: may cause overheating.
- Incorrect fastening: using plastic ties for fire‑rated lines, over‑tightening that deforms the cable.
- Absence of labeling: complicates installation, maintenance and fault location.
6. Features of control cable installation
- Route preparation: Before work begins, the route must be cleared of debris, boulders and sharp objects. For underground laying, the trench bottom is leveled and covered with sand.
- Cable payout: The cable must be pulled off the reel, not pulled in loops. Tension exceeding permissible values (usually not more than 50 N/mm² for copper conductors) is not allowed.
- Joining and termination:
- Cable preparation must follow technology that prevents nicking of conductors and insulation.
- Special joints (straight, branch) appropriate for the laying conditions are used for connecting conductors.
- Stranded conductors require crimping with ferrules (NSHVI, NVI) for reliable contact in terminals.
- Shielding: If shielded control cable (KVVGE) is used, the shield must be grounded at one end (typically at the receiving equipment side) to protect against electromagnetic interference.
- Labeling: Each cable must have tags indicating the brand, cross‑section, voltage, line number. On connecting joints, the installation date is indicated.
- Post‑installation tests: After laying is completed, electrical measurements are performed: insulation resistance, conductor continuity check, high voltage test (for cables rated above 1 kV).
7. Conclusion
Proper laying of control cables is a comprehensive task that requires consideration of many factors: from selecting the optimal installation method (in trays, pipes, trenches) to strict compliance with PUE requirements and rules for joint laying. Only such an approach guarantees reliable and long‑lasting operation of automation, signaling and control systems.
A key success factor is also the use of high‑quality, certified materials. The range of control cables from JSC “Kazenergocable” includes a full spectrum of solutions for any laying method: KVVG for indoor applications, AKVVG with aluminum conductors for cost‑effective solutions, as well as armored versions (KVBbShv) for underground laying and versions with “ng‑LS” indices to ensure fire safety. All products are manufactured in accordance with GOST and are accompanied by the necessary documentation. You can view the full range in the cable catalog section.
