Combustible gas alarm wires can be routed through instrument cable trays

Combustible gas alarm wiring can be routed through instrument cable trays if the cables are approved for hazardous locations and proper separation and installation practices are followed.

Cable Tray Use in Hazardous Locations

Instrument cable trays are commonly used to support and route signal and control wiring, including combustible gas alarm circuits, in industrial plants. However, the acceptability of routing such wiring through trays depends on the cable type, hazardous area classification, and compliance with electrical codes. For example, in Class I, Division 2 areas (where flammable gases may be present under abnormal conditions), Instrumentation Tray Cable (ITC) or other listed cables may be used in trays without spacing or single-layer restrictions.

Cable Types and Safety Considerations

Type IT

C or MC cables are typically permitted for hazardous locations, provided they are listed for the specific class/division. Intrinsically Safe (IS) circuits, such as combustible gas alarms, can be installed in the same tray as non-IS circuits if separated by at least 2 inches, a grounded metal partition, or an approved insulating barrier. Metal-clad or armored cables may allow IS and non-IS circuits to share a tray without separation if the sheath can carry fault current to ground.

Installation Guidelines

Cable trays should be mechanically supported along their entire run to prevent stress on the conductors. Trays must comply with ampacity, grounding, fill, and spacing requirements as per NEC Article 318. Avoid routing trays through hot environments, areas prone to spillage, or locations where escaping gases could accumulate, to minimize fire hazards.

Junction boxes and terminations must meet hazardous area requirements, and cable joints should be limited to approved points.

Best Practices

Keep cable runs as short as possible and avoid obstructing maintenance access. Use fire-resistant or UV-resistant insulation for exposed trays. Maintain segregation of power and signal cables to reduce interference and ensure safety.

In summary, combustible gas alarm wiring can be routed through instrument cable trays if the cables are listed for the hazardous location, proper separation from non-IS circuits is maintained, and installation follows NEC and IEC 60079-14 guidelines for hazardous areas. Proper planning, cable selection, and adherence to safety standards are essential to prevent ignition hazards and ensure reliable operation.