Cable tray

Piperack is the elevated supporting stmcture used to convey piping between equipment. This stmcture is also utilized for cable trays associated with electric power distribution and for instmment trays. 

Electric Tracing An electric tracing system (see Fig. 10-178) consists of an electric heater placed against the pipe under the thermal insulation, the supply of electricity to the tracer, and any control or monitoring system that may be used (optional). The supply of electricity to the tracer usually consists of an electrical panel and electrical conduit or cable trays. Depending on the size or the tracing system and the capacity of the existing electrical system, an additional transformer may be required. 

Failure of power or controls to the valve (generally related to the seismic capacity of the cable trays, control room, and emergency power). These failure modes are analyzed as failures of separate systems linked to the equipment since they are not related to the specific piece of equipment (i.e., a motor-operated valve) and are common to all active equipment. 

Considering the relatively small, controlled amount of com-husfihles in an LWR, it is surprising Jiiit fiiL S at nuclear power plants. should be important. The first incident to attract attention was the fire in the San Onofre cable trays (FRPJ). This was followed by spontiiiieous combustion of uncured polyurethane foam in the cable seals at Peach Bottom 1 (1971). The incident at Browns Ferry in 1975 was similar, except that a candle ignited the polyurethane foam. These events showed the effectiveness of fire as an initiator of multiple system failures -... 

Siu, N. and G. Apostolakis, 1982, Probabilistic Models for Cable Tray Fires, Rclinbility Engineering 3, p 213. 

Many materials are subject to deterioration by ultraviolet light (UV). particularly many of the plastics and fiberglass materials. Fiberglass materials for outside use should be specified as UV-stabilized, and most plastics installed outdoors should be carbon-impregnated (black in color). It is particularly recommended that plastic cable ties, which secure cables in cable trays, be carbon-impregnated if installed outdoors. 

MG 2 Safety Standard for Construction and Guide for Selection, Installation, and Use of Electric Motors and Generators MG 10 Energy Guide for Selection and Use of Polyphase Motors VE 1 Cable Tray Systems... 

Normally a specialist works application these materials are useful protective coatings for such items as cable trays and switch boxes. They are also used for the externals of pipelines. 

A great variety of PVC materials have been tested in the process thus far cable, cable trays, flooring material, window frames, artificial leather, packaging, pipes, flexible hoses, ring binders and roofing material. This indicates that the process is robust and can handle a broad range of PVC materials. In terms of chlorine content, there are no restrictions. With the completion of the pretreatment pilot plant, the contents of other plastics and metals may now be reduced significantly. 

Protection of pipe racks and cable trays from fire. 

Process Facilities 15 Area electrical classification 16 Accessibility for mechanical integrity (sampling, maintenance, repairs) 17 Protection of piping and vessels from vehicles and forklifts 18 Protection of small-bore lines, fittings from external impact, personnel 19 Routing of process piping, critical controls cable trays, critical utilities 20 Vent, drain, and relief valve discharge locations... 

Cable trays Not less than 0.3 gpm/ft2 of projected plane area (horizontal or vertical). 

The process area has combustible gas detectors, fireproofing, and a water deluge system. Cable trays are protected with deluge, and portable dry chemical extinguishers are in the process area. Diesel-powered fire water pumps can provide a maximum fire water demand for 4 hr. 

Onshore 2 inches of Concrete UL 1709, 2 hour rating Offshore Ablative or intumensent materials, UL 1709, 2 hour rating Cable Trays Stainless steel cabinets or fire rated mats, UL 1709, 20 minute rating ESD Control Panels. Stainless steel cabinets or fire rated mats, UL 1709, 20 min. rating EIVs. (If directly exposed) -Stainless steel cabinets or fire rated mats UL 1709, 60 min. EIV actuators Stainless steel cabinets or fire rated mats UL 1709, 20 minute rating Firewalls ... 

Ancillaries Pipe racks and cable trays that are in place adjacent to the existing building will require special attention. Penetrations in the new wall are necessary for power cables and instrument lines, These openings should not adversely affect the pressure rating of the building. 

If fiber optics are going to be nsed, what physical distances are involved, and what civil engineering costs are implied (for gantry, cable tray, condnit, tnnneling etc) ... 

Fire damage to cable trays can be caused by exposure to flames and heat from spill or pool fires below, falling burning liquids from above, thermal radiation from an adjacent fire, or fire originating among the cables themselves. Cable trays and other grouped cable, wire, and nonmetallic tubing runs should be evaluated to determine the potential for fire exposure where warranted by their size and cost or safety-related importance of their service. 

Cable trays outside of process areas or unit battery limits are normally not provided with either passive or active fire protection regardless of size. Small cable trays are usually not fire protected regardless of location when they provide service for ancillary equipment or for equipment designed to fail to a safe state on loss of power, control signal or communication. 

Primary cable trays inside of process areas, process structures, or unit battery limits should be reviewed to determine if their routing or location presents a potential fire exposure. Potential external fire exposures to cable trays are typically at those locations where flammable or combustible liquids or gases are handled, such as ... 

Cable trays may be protected by water spray or fire resistant material. Large or fully filled cable trays, particularly those carrying power cables, should also be reviewed for cable overloading that could result in wire overheating and internal fire. 

NFPA15 provides guidance on water spray protection for cable trays and other grouped cable, wire, and nonmetallic tubing runs. These options are summarized in Table 8-10. 

In all of the cases where protection from a spill or pool fire is justified, the structural supports for the cable trays also require fire protection. Protection... 

Protection Options for Cable Trays Exposed to Spill Fires... 

Spill fire (no protection) Water spray cable tray only 0.30 gpm/ft (12.2 (Ipm/mh Top and bottom (or both sides)... 

Fire originating in cable tray itself tray ... 

For very large cable tray arrays and multiple trays and levels, additional guidance can be found in NFPA 850, Appendix C-4, Grouped Cable Fire Tests. 

Flame shields on the underside of cable trays have been used effectively to deflect flames or heat emanating from fires below. Flame shields should be fabricated of Xein (1.6-mm) thick steel plate or equivalent mounted below the cable tray and extending a minimum of 6 in (152 cm) beyond the tray side rails. These shields can improve tray survivability usually in concert with water spray systems. Flame shields alone (with no water spray) can provide only brief fire protection and are not normally used in this manner. Flame shields coated with... 

Cable tray fires have resulted from the accumulation of process leakage, residues or combustible dusts or debris on top of cable trays with densely packed wires and cables. Covering shields above cable trays have been used to minimize such accumulations however, such shields should be used with caution as they can limit air circulation and increase cable and wire temperatures in densely loaded trays particularly those carrying power cables. Covering shields may also block fixed fire protection water spray or manually applied firefighting water spray from reaching the cables. 

Main banks of aboveground instrument runs in cable trays (such as those coming from the control room and supported on process unit pipe racks) that are located inside process unit battery limits should be considered for fireproofing by one of the following passive methods ... 

Mineral wool/cement board—Perforated and solid sheet metal and ladder-type cable trays can be completely enclosed with 1 in (25 mm) minimum thickness mineral wool/cement board panels, or equivalent. The panels should be secured with stainless steel screw and stainless steel bands in (19 mm) wide by 0.02 in (0.5 mm) thick, located no more than 18 in (450 mm) apart. In freezing climates the fireproofing panels should be given a weatherproof coat of paint. The structural strength of the metal cable tray should be adequate to support the weight of the fireproofing. 

Large numbers of wood pallets can present a serious fire threat if stacked outdoors, too close to processing structures and areas, cable trays, pipe racks, tanks, power lines, buildings, and warehouses. Some commonly used separation distances are shown in Table 8-15. 

Where large cable trays feed into the control building or I/O room, these openings or wall penetrations should be sealed against fire and smoke. Penetration seals should be provided that are or should meet the appropriate test requirements of ASTM E 814, Standard Method of Fire Tests of Through-Penetration Fire Stops or other test methods, such as IEEE 634, Testing of Fire Rated Penetration Seals. 

I n larger MCCs, if the combustible loading gets extensive, then passive fire protection, e.g., fire-resistant cables or passive fire protection should be considered. The practices of using multiple tiers of cable trays or stripping the outer jacket insulation (to make the cable easier to handle after it enters the room or cabinet) are not recommended. 

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