Laying the cable in the tray or in the pipe: What should I choose?

Introduction: Two Ways to Organize a Cable Route

Cable laying inside buildings, on open trestles, and underground requires choosing a support system: a tray or a pipe. A tray is an open metal or plastic structure onto which cables are laid on top and secured. A pipe is a closed circular channel into which the cable is pulled. Both methods solve the common task of protecting and organising cable lines, but they do it differently. A tray provides easy access and good cooling, while a pipe offers tightness and high mechanical protection.

The choice between tray and pipe affects the final estimate, installation speed, fire safety, and permissible current loads. In production shops, trays are more common; in residential and office buildings, pipes and corrugated conduits are used. Underground, HDPE pipes are virtually the only option for non‑armoured cables, while trays are not used overhead at all. For more details on laying power lines, see the article power cable laying; about optics — optical cable laying. Features of overhead routes are covered in SIP laying, and low‑current networks — in UTP cable laying. A comparison of underground vs. overhead methods is given in underground or overhead.

Comparison Table: Cable Laying in Tray vs. Pipe

Regulatory Requirements: PUE and GOST

The 7th edition of PUE regulates laying methods depending on room category and cable type. For open laying in production premises, trays and boxes are permitted, while the distance between power and low‑current cables must be at least 0.5 m when laid in parallel. In residential and public buildings, concealed wiring is done in PVC pipes or corrugated conduits with a non‑combustibility index ng. GOST 31565‑2012 establishes fire safety for cable lines: joint laying of mutually redundant circuits in the same tray without fire‑resistant partitions is not allowed.

The pipe fill factor should not exceed 0.4 for two or more cables; otherwise pulling force and overheating increase. For trays, fill factor by cross‑sectional area is regulated by the manufacturer, usually no more than 40–50% taking ventilation into account. Underground, HDPE pipes are laid with double‑wall design to withstand crushing. Regulations for fibre‑optic and UTP lines are similar, but allow smaller bending radii. Detailed rules for each cable type can be found in the respective guides.

Design Features and Materials

Trays come in ladder, sheet, wire, and mesh types. A ladder tray consists of two longitudinal beams connected by rungs, providing maximum ventilation. Sheet trays have a solid bottom, protecting against dust and drips, but reduce heat dissipation. Wire trays made of welded mesh are lightweight and used for low‑current networks. Materials include galvanised steel, stainless steel, and aluminium. Fixing to ceilings, walls, and trestles is done with brackets.

Pipes for cable laying are divided into smooth rigid PVC, HDPE, steel, and flexible corrugated. Smooth pipes are used for concealed wiring in walls and floors; corrugated – for suspended ceilings and movable joints. Double‑wall HDPE pipes with a smooth inner layer are intended for underground laying. Steel pipes are required in explosion‑hazard zones and for protection against rodents. Vertical laying in pipes requires fire‑stop barriers every 20–30 m to prevent flame spread.

Thermal Conditions and Ventilation

An open tray allows the cable to cool by natural convection. Permissible continuous currents for cables laid in air in trays are higher than in pipes, according to PUE tables. For a copper cable of 2.5 mm² cross‑section, the current in a tray is 25 A, while in a pipe it is 21 A. For group laying in a tray in bundles, a derating factor of 0.7–0.9 is applied depending on the number of cables. In a pipe, the reduction factor is even lower due to the enclosed volume. Therefore, for high‑current circuits, trays are preferable.

The pipe limits heat dissipation but protects the cable from external heating. In hot workshops, this can be an advantage if the pipe shields against radiation. In cold rooms, the pipe slows cooling, reducing condensation. For fibre optics and UTP, thermal conditions are less critical, but high temperature inside the pipe accelerates insulation ageing. Therefore, in hot environments for power lines, either a tray or a larger‑diameter pipe with ventilation gaps is better.

Protection Against Mechanical Damage

A tray protects the cable only from below and from the sides; the top is open. Accidental tool impact, falling objects, or stepping can damage the cable. Therefore, trays are mounted at least 2 m high in passageways, or sheet trays with covers are used. A cover turns the tray into a closed box, approaching pipe‑level protection but reducing ventilation. In production shops with cranes and loaders, trays without covers are not allowed.

A pipe provides enclosed mechanical protection around the entire perimeter. Steel pipe withstands strong impacts, crushing, and rodent attacks. HDPE pipe underground protects against stones and soil pressure. Corrugated PVC pipe is lightweight but less robust than smooth. For underground laying, double‑wall pipes are mandatory to handle soil and traffic loads.

Fire Safety

Metal trays and pipes do not support combustion and do not emit smoke. Plastic trays and pipes must be made of polymers with an ng (non‑combustible) index per GOST 31565. In public buildings, concealed laying in plastic pipes without an ng certificate is prohibited. Steel pipes additionally contain a fire: the cable inside prevents flames from spreading outward, but the cable itself must be ng‑LS to avoid toxic smoke.

In vertical pipes, fire can propagate along the channel as through a chimney. Therefore, fire‑stop couplings or filling with fire‑resistant foam are installed every 20–30 m. In covered trays, the risk is lower, but plastic covers emit smoke during fire. Thus, from a fire safety standpoint, both methods require the use of ng‑LS cables and proper design.

Installation, Labour Intensity, and Cost Estimates

Laying cable on a tray is faster: the cable is rolled out over rollers, then lowered to the bottom and secured with clamps. The installer does not spend time on pulling into a pipe. For long straight runs, a tray saves up to 50% of time. However, the tray itself requires installation: brackets, supports, fasteners. In tight spaces, pipes are simpler: they are fixed to the wall with clips, and the cable is pulled using steel wire.

The cost estimate according to GESN includes rates for installing trays and pipes. The cost of a tray with fastenings is lower than the sum of pipes, fittings, pulling, and connectors for large facilities. For short runs up to 10 metres, a pipe is cheaper. Cable consumption also matters: with bends, the length increases by 5‑15% due to radii. In a tray, turns are made with the minimum cable bending radius, saving material.

When to Choose Laying in a Tray

• Production workshops and cable floors where easy access for maintenance and adding lines is needed.
• High‑power power routes with many cables requiring good cooling.
• Trestles and galleries on industrial sites where rapid deployment is important.
• Low‑current networks in server rooms and data centres where frequent re‑patching occurs.
• Rooms without aggressive environment and with sufficient ceiling height for tray mounting.

When to Choose Laying in a Pipe

• Concealed wiring in residential and office buildings: in walls, floors, behind drywall.
• Underground laying of non‑armoured cables in HDPE pipes.
• Rooms with high humidity, dust, or chemically aggressive environment – sealed pipe protects the cable.
• Explosion‑hazard zones requiring steel pipe.
• Temporary structures where pipe can be quickly dismantled and relocated.

Typical Mistakes in Selection and Installation

• Laying power cables closely bunched in a tray without derating factors – cable overheats, insulation ages.
• Filling a pipe to more than 40% – pulling becomes impossible, cable is damaged.
• Using PVC pipe without ng rating in a public building – violation of fire regulations.
• Placing cable on a tray without clamp fastening – cables can fly apart during a short circuit.
• Using steel pipe without earthing – stray currents and corrosion appear.
• No fire‑stop barriers in vertical pipes – creates a smoke duct.

Frequently Asked Questions

What is the difference between a tray and a pipe?

A tray is an open structure, a pipe is a closed channel. A tray provides cooling and access, a pipe provides sealing and protection.

Can power cable be laid in corrugated conduit?

Yes, if the corrugated conduit is PVC ng and the diameter is chosen with a fill factor of no more than 40%. For high‑power lines, rigid pipe is better.

Which method is cheaper for a large number of cables?

A tray is usually more economical for large volumes due to lower labour and fitting costs.

What is better for underground laying – tray or pipe?

Only HDPE pipe or armoured cable in the ground. Trays are not used underground.

What is the current derating factor for laying in a pipe?

Per PUE, for two cables in a pipe the factor is 0.85, for four – 0.7. Exact values depend on the method and number of cables.

Does a metal tray need earthing?

Yes, all metal cable support structures must be earthed for protection against indirect contact and potential equalisation.

Conclusion

A tray and a pipe are two tools, each for its own task. A tray is indispensable where cooling, access, and speed of deployment matter. A pipe is used where sealing, concealment, and maximum protection are required. A wrong choice leads either to cable overheating or to unjustified costs. Compliance with PUE and GOST during design guarantees a long service life for the cable route, whichever method is chosen.