An electrical cable supporting structure, a cable tray system, is essential in the electrical wiring of buildings. It is specifically designed to hold insulated electrical cables used for power distribution, control, and communication. Typically, cable trays serve as a substitute for open wiring or electrical conduit systems, and they are frequently employed for effective cable management within commercial and industrial constructions. These trays prove particularly advantageous when modifications to a wiring system are expected, permitting straightforward installation of new cables simply by placing them in the tray instead of maneuvering them through a conduit.

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As stated in the National Electrical Code standard in the United States, a cable tray constitutes a unit or assembly of units or sections along with corresponding fittings to form a reliable structural system crucial for securely fastening or providing support to cables and raceways.

Types

Different types of trays cater to various applications. For instance, a solid-bottom tray offers optimal protection for cables but necessitates the use of fittings or cutting the tray to access the cables. A deep, solid enclosure for cables is known as a cable channel or cable trough.

A ventilated tray, engineered with openings at its bottom, allows airflow around the cables, enhances water drainage, and facilitates the descent of dust. Smaller cables can exit the tray through these ventilation openings, which may appear as slots or punched holes. Meanwhile, a ladder tray raises cables via transverse bars, resembling ladder rungs, at consistent intervals of approximately 4 to 12 inches (100 to 300 mm).

Both ladder and ventilated trays may feature solid covers to safeguard cables from falling objects, dust, and water. Outdoors or in dusty locations, these covers are often peaked to prevent the accumulation of debris, including dust, ice, or snow. Lightweight cable trays are more suitable in settings with numerous small cables, such as computer networking—these can be constructed from wire mesh, referred to as a "cable basket," or designed as a single central rail with ribs for cable support.

Channel trays provide economical support for cable drops and branch runs from the main cable tray system, particularly in installations where the tray cable quantity is limited, and conduit is not preferred.

Large power cables within the tray may require support blocks to maintain adequate spacing between conductors and prevent wire overheating. In contrast, smaller cables can either be laid unsecured in horizontal trays or secured using cable ties within vertically mounted trays.

To ensure cable support during elevation or directional changes in a tray, numerous specialized fittings are tailored to match various styles and manufacturers. Horizontal elbows redirect the tray within the same plane and can come in angles of 30, 45, and 90 degrees, while inside and outside elbows accommodate changes perpendicular to the tray. Various shapes, including tees and crosses, are available, and some types and manufacturers offer adjustable elbows for precise field fitting around obstacles.

A comprehensive functional tray system utilizes assorted clamping, supporting, and splicing accessories—different sizes of cable trays used within a single run can connect with reducers.

Materials Used

Common cable trays are fashioned from galvanized steel, stainless steel, aluminum, or glass-fiber reinforced plastic. The choice of material is typically dictated by the specific application requirements. Galvanized trays may feature pre-galvanized steel sheets prepared into tray form or might undergo hot-dip galvanization post-fabrication. If a galvanized tray is cut to length on-site, the cut edges are usually treated with a zinc-rich compound to guard against corrosion.

Fire Safety Concerns and Solutions

The presence of combustible cable jackets raises significant fire hazard concerns, as cable fires can proliferate along trays within structures. This risk is effectively mitigated through fire-retardant cable jackets or fireproof coatings applied to the cables. It's essential to recognize that heavy coatings or prolonged fire-stopping measures can necessitate adjustments to cable current ratings, as these fireproofing tactics may compromise heat dissipation of the cables.

Regular cleaning is critical for maintaining safety, considering cable trays are often situated in inaccessible areas. If left unchecked, combustible dust and clutter can accumulate in the trays.

Plastic and fiberglass-reinforced plastic cable trays pose a fire risk, but the use of fire retardants or fireproofing measures can help mitigate this concern.

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Ferrous cable trays expand when exposed to heat from accidental fires. This was confirmed by the German Otto-Graf-Institut Test Report III.1-/Tei/tei, which illustrates how "soft" firestops, such as those made from fibrous insulation with rubber coatings, can be dislodged. The same applies to silicone foam seals, which can be effectively resolved through the use of firestop mortars with suitable compression strength and thickness, as elaborated previously. Additionally, certain building codes stipulate that penetrants like cable trays be installed in ways that prevent their contribution to the collapse of a firewall.

See Also

• Passive fire protection
• Circuit integrity
• Intumescent
• Endothermic
• Conduit (electrical)

Processing of Perforated Cable Trays