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| {{Short description|Electrical-cable-supporting structure}} | |||
| A '''''' system, according to the US National Electrical Code, is "a unit or assembly of units or sections and associated fittings forming a rigid structural system used to securely fasten or support ]s and ]s." are used to hold up and distribute cables, as an alternative to open wiring or electrical conduit systems. Cable trays are especially useful where changes to a wiring system are anticipated, since new cables can be installed by laying them in the tray, instead of pulling them through a pipe. Cable trays are commonly used for cable managment in commercial and industrial construction. | |||
| {{more citations needed| date= September 2010}} | |||
| {{stack| | |||
| {{Electrical Wiring Sidebar}} | |||
| ⚫ | ] | ||
| ⚫ | ]ped cable tray penetration with ] cables]] | ||
| ⚫ | ] in ], showing rapid fire spread through burning of cable jackets from one cable tray to another]] | ||
| ⚫ | ] | ||
| }} | |||
| In the ] of buildings, a '''cable tray''' system is used to support insulated ]s used for power distribution, control, and communication. Cable trays are used as an alternative to open wiring or ] systems, and are commonly used for cable management in commercial and industrial construction. They are especially useful in situations where changes to a wiring system are anticipated, since new cables can be installed by laying them in the tray, instead of pulling them through a pipe. | |||
| According to the ] standard of the ], a cable tray is a unit or assembly of units or sections and associated fittings forming a rigid structural system used to securely fasten or support cables and raceways.<ref>NEC, 2017, {{ISBN|978-1455912797}}</ref> | |||
| ⚫ | == |
||
| ⚫ | Several types of tray are used in different applications. |
||
| ⚫ | ==Types== | ||
| ⚫ | A ventilated tray has openings in the bottom of the tray, allowing some air circulation around the cables, water drainage, and |
||
| ⚫ | Several types of tray are used in different applications. A solid-bottom tray provides the maximum protection to cables, but requires cutting the tray or using fittings to enter or exit cables. A deep, solid enclosure for cables is called a cable channel or cable trough.<ref name=Steward10>W.E. Steward and R.A. Beck, ''Modern Wiring Practice'', Newnes, London, 2010 {{ISBN|978-1-85617-692-7}}, pages 266-272.</ref> | ||
| ⚫ | A ventilated tray has openings in the bottom of the tray, allowing some air circulation around the cables, water drainage, and allowing some dust to fall through the tray. Small cables may exit the tray through the ventilation openings, which may be either slots or holes punched in the bottom. A ladder tray has the cables supported by a traverse bar, similarly to the rungs of a ladder, at regular intervals on the order of 4 to 12 inches (100 to 300 mm). | ||
| Ladder and ventilated trays may have solid covers to protect cables from falling objects, dust, and water. Tray covers for use outdoors or very dusty locations may have a peaked shape to shed snow, ice or dust. | |||
| Ladder and ventilated trays may have solid covers to protect cables from falling objects, dust, and water. Tray covers for use outdoors or in dusty locations may have a peaked shape to shed debris including dust, ice or snow. Lighter cable trays are more appropriate in situations where a great number of small cables are used, such as for telephone or computer network cables. These trays may be made of wire mesh, called "cable basket",<ref name=Steward10/> or be designed in the form of a single central spine (rail) with ribs to support the cable on either side. | |||
| Channel Tray provides an economical support for cable drops and branch cable runs from the backbone cable tray system. Channel cable tray is used for installations with limited numbers of tray cable when conduit is undesirable.<ref>Conduit or Cable Tray, the easy guide, Nov 27, 2017,http://www.t-trayusa.com/blog/2017/11/25/conduit-or-cable-tray-the-easy-guide {{Webarchive|url=https://web.archive.org/web/20181008101331/http://www.t-trayusa.com/blog/2017/11/25/conduit-or-cable-tray-the-easy-guide |date=2018-10-08 }}. Retrieved 2017 Nov 29</ref> | |||
| ⚫ | Large power cables laid in tray may require support blocks to maintain spacing between conductors to prevent overheating of wires. Smaller cables may be laid unsecured in |
||
| ⚫ | Large power cables laid in the tray may require support blocks to maintain spacing between conductors, to prevent overheating of the wires. Smaller cables may be laid unsecured in horizontal trays, or secured with ] to the bottom of vertically mounted trays.<ref>Wiring duct cable,https://bazaredakt.ir/full-introduction-to-alborz-duct/</ref> | ||
| ⚫ | To maintain support of cables at changes of elevation or direction of a tray, a large number of specialized cable tray fittings are made compatible with each style |
||
| ⚫ | To maintain support of cables at changes of elevation or direction of a tray, a large number of specialized cable tray fittings are made compatible with each style and manufacturer. Horizontal elbows change direction of a tray in the same plane as the bottom of the tray and are made in 30, 45 and 90 degree forms; inside and outside elbows are for changes perpendicular to the tray bottom. These can be in various shapes including tees and crosses. Some manufacturers and types provide adjustable elbows, useful for field-fitting a tray around obstacles or around irregular shapes.<ref>http://www.tnb.com/contractor/docs/cabletray_us_revised_lr.pdf {{Webarchive|url=https://web.archive.org/web/20100103092350/http://tnb.com/contractor/docs/cabletray_us_revised_lr.pdf# |date=2010-01-03 }} One manufacturer's cable tray catalog, retrieved 2010 Aug 11.</ref> | ||
| ⚫ | Various clamping, supporting and splicing accessories are used with cable tray to provide a complete |
||
| ⚫ | Various clamping, supporting and splicing accessories are used with the cable tray to provide a complete functional tray system. For example, different sizes of cable tray used within one run can be connected with reducers. | ||
| == Materials used == | == Materials used == | ||
| Common cable trays are made of galvanized ], ], aluminum, or glass-fiber |
Common cable trays are made of galvanized ], ], aluminum, or glass-fiber reinforced plastic. The material for a given application is chosen based on where it will be used.<ref>{{Cite web |url=http://www.t-trayusa.com/blog/2017/11/25/conduit-or-cable-tray-the-easy-guide |access-date=2017-11-29 |title=Archived copy |archive-date=2018-10-08 |archive-url=https://web.archive.org/web/20181008101331/http://www.t-trayusa.com/blog/2017/11/25/conduit-or-cable-tray-the-easy-guide |url-status=dead }}</ref> Galvanized tray may be made of pre-galvanized steel sheet fabricated into tray, or may be hot-dip galvanized after fabrication. When galvanized tray is cut to length in the field, usually the cut surface will be painted with a zinc-rich compound to protect the metal from corrosion. | ||
| == Fire safety concerns and solutions == | == Fire safety concerns and solutions == | ||
| Combustible cable jackets may catch on fire and cable fires can thus spread along a cable tray within a structure. This is easily prevented through the use of fire-retardant cable jackets or ] |
Combustible cable jackets may catch on fire and cable fires can thus spread along a cable tray within a structure. This is easily prevented through the use of fire-retardant cable jackets, or ] coatings applied to installed cables. Heavy coatings or long fire-stops may require adjustment of the cable current ratings, since such fireproofing measures may reduce the heat dissipation of installed cables.<ref>{{cite web|last1=Jones|first1=Dean|title=Cable Trays Make it Easy to Repair & Maintain Cables in Industrial Settings|url=http://commercialelectriciansperth.com.au/cable-trays/|publisher=Commercial Electricians Perth|accessdate=15 September 2014|archive-url=https://web.archive.org/web/20140917233537/http://commercialelectriciansperth.com.au/cable-trays/#|archive-date=2014-09-17|url-status=dead}}</ref> | ||
| Regular housecleaning is important for safety, as cable trays are often installed in hard to reach places. Combustible dust and clutter may accumulate if the trays are not routinely checked and kept clean. | |||
| Plastic and fibreglass reinforced plastic are combustible |
Plastic and fibreglass reinforced plastic cable trays are combustible; the effect is mitigated through the use of fire retardants or fireproofing. | ||
| Ferrous cable trays expand with the increasing |
Ferrous cable trays expand with the increasing heat from accidental fire. This has been proven by the German Otto-Graf-Institut Test Report III.1-80999/Tei/tei "Supplementary Test On The Topic Of Mechanical Force Acting On Cable Penetration Firestop Systems During The Fire Test", dated 23 October 1984, to dislodge "soft" ]s, such as those made of fibrous insulations with rubber coatings. This also applies to any ] foam seals, but is easily remedied through the use of ] of sufficient compression strength and thickness, as shown above. Also, some ]s mandate that ]s such as cable trays are installed in such ways so as to avoid their contribution to the collapse of a ]. | ||
| ] | |||
| == Fireproofing == | |||
| ] and ]ping systems are ] measures. | |||
| The cable trays themselves are only of concern if they are made of plastic. Typically, what is of most concern is the items placed upon the trays. In some cases, the primary concern is to mitigate the fuel load that the cable jacketing represents. As cable jackets burn, smoke is produced, containing ] as one of the combustion by-products. Chlorine bonds with airborne moisture, yielding ], which contributes to corrosion damage after the fire. | |||
| Mitigation methods include the use of fire retardants, as well as concealment, panelling and fire-resistant wraps. Cables certified as ''low smoke-producing '' or ''resistant to the spread of fire ''<ref>NFPA 70 National Electrical Code 2008 Edition / Chapter 7 Special Conditions / ARTICLE 725 Class 1, Class 2, and Class 3 Remote-Control, Signaling, and Power-Limited Circuits / IV. Listing Requirements, 725.179</ref> produce limited amounts of smoke and combustion. The other concern is ]. Particularly, though not exclusively in ]s, it is necessary to maintain the operability of cables during a fire, so that critical equipment, such as reactor cores, safety valves, etc. can be shut down, to prevent a catastrophe. Mineral insulated cables are inherently fire-resistant. | |||
| Boxes or wraps constructed of fire resistant materials may also be used to isolate heat from the cables. Boxes and wraps must be accounted for in four respects: | |||
| * The added weight must be included in support calculations, hanger sizing and spacing, as well as seismic calculations. | |||
| * Boxes and wraps inhibit the ability of power cables to disperse operational heat. The hotter the cable, the less energy can be conducted. The difference between the unwrapped and the wrapped (or boxed) conductivity is quantified as a percentage, which is referred to as Ampacity Derating. If, for instance, a certain fireproofing system causes the ampacity to be lowered by 40%, then 40% more cables are needed to conduct the same amount of electricity. Ampacity derating is remedied through the use of purpose-designed "windows" that allow air flow during normal operations, but shut if exposed to the heat from accidental fires. | |||
| *Hanger systems may also need to be fireproofed. | |||
| *Firestops around penetrating cable trays that have been fireproofed must have been included at the time of test so that compatibility between firestopping and fireproofing can be documented. Chemical compatibility between the two systems should be checked to avoid longterm operational degradation. | |||
| == Images == | |||
| <gallery widths=175px heights=200px perrow=3> | |||
| ⚫ | |||
| ⚫ | |||
| Image:Tray cross barrier.jpg|Cable tray cross barrier firestop test, full scale wall, in ] as per DIN4102. | |||
| ⚫ | |||
| Image:Domtar.JPG|Cable tray with inoperable ] in ] pulp and paper mill. | |||
| Image:German tray 1.jpg|Cable tray penetration in Lingen/Ems, ]. The tray stops short of the fire barrier to prevent damage from heat expansion of the tray during an accidental fire. | |||
| Image:Promat signum tray cladding 2.jpg|] ] of cable trays in Lingen/Ems, ] using ] board ] qualified to DIN 4102. Contractor: Signum, ], Germany. | |||
| Image:Tray dirt.jpg|Cable trays in cable spreading room of a ], ], ]. This picture shows how combustibles, such as ], ], ] and ] can build up on cable trays. ] even in hard-to-reach places mitigates ]s. | |||
| ⚫ | |||
| </gallery> | |||
| == See also == | == See also == | ||
| <div style="-moz-column-count:2; column-count:2;"> | |||
| * ] | |||
| * ] | |||
| * ] | * ] | ||
| * ] | * ] | ||
| * ] | |||
| * ] | |||
| * ] | |||
| * ] | * ] | ||
| * ] | * ] | ||
| * ] | * ] | ||
| </div> | |||
| ==References== | ==References== | ||
| {{reflist}} | |||
| <references/> | |||
| {{commons category|Cable trays}} | |||
| ⚫ | ] | ||
| ⚫ | ] | ||
| ] | |||
| ] | |||
Latest revision as of 11:19, 24 May 2024
Electrical-cable-supporting structure | This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. Find sources: "Cable tray" – news · newspapers · books · scholar · JSTOR (September 2010) (Learn how and when to remove this message) |
| Electrical installations |
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| Wiring practice by region or country |
| Regulation of electrical installations |
| Cabling and accessories |
| Switching and protection devices |
In the electrical wiring of buildings, a cable tray system is used to support insulated electrical cables used for power distribution, control, and communication. Cable trays are used as an alternative to open wiring or electrical conduit systems, and are commonly used for cable management in commercial and industrial construction. They are especially useful in situations where changes to a wiring system are anticipated, since new cables can be installed by laying them in the tray, instead of pulling them through a pipe.
According to the National Electrical Code standard of the United States, a cable tray is a unit or assembly of units or sections and associated fittings forming a rigid structural system used to securely fasten or support cables and raceways.
Types
Several types of tray are used in different applications. A solid-bottom tray provides the maximum protection to cables, but requires cutting the tray or using fittings to enter or exit cables. A deep, solid enclosure for cables is called a cable channel or cable trough.
A ventilated tray has openings in the bottom of the tray, allowing some air circulation around the cables, water drainage, and allowing some dust to fall through the tray. Small cables may exit the tray through the ventilation openings, which may be either slots or holes punched in the bottom. A ladder tray has the cables supported by a traverse bar, similarly to the rungs of a ladder, at regular intervals on the order of 4 to 12 inches (100 to 300 mm).
Ladder and ventilated trays may have solid covers to protect cables from falling objects, dust, and water. Tray covers for use outdoors or in dusty locations may have a peaked shape to shed debris including dust, ice or snow. Lighter cable trays are more appropriate in situations where a great number of small cables are used, such as for telephone or computer network cables. These trays may be made of wire mesh, called "cable basket", or be designed in the form of a single central spine (rail) with ribs to support the cable on either side.
Channel Tray provides an economical support for cable drops and branch cable runs from the backbone cable tray system. Channel cable tray is used for installations with limited numbers of tray cable when conduit is undesirable.
Large power cables laid in the tray may require support blocks to maintain spacing between conductors, to prevent overheating of the wires. Smaller cables may be laid unsecured in horizontal trays, or secured with cable ties to the bottom of vertically mounted trays.
To maintain support of cables at changes of elevation or direction of a tray, a large number of specialized cable tray fittings are made compatible with each style and manufacturer. Horizontal elbows change direction of a tray in the same plane as the bottom of the tray and are made in 30, 45 and 90 degree forms; inside and outside elbows are for changes perpendicular to the tray bottom. These can be in various shapes including tees and crosses. Some manufacturers and types provide adjustable elbows, useful for field-fitting a tray around obstacles or around irregular shapes.
Various clamping, supporting and splicing accessories are used with the cable tray to provide a complete functional tray system. For example, different sizes of cable tray used within one run can be connected with reducers.
Materials used
Common cable trays are made of galvanized steel, stainless steel, aluminum, or glass-fiber reinforced plastic. The material for a given application is chosen based on where it will be used. Galvanized tray may be made of pre-galvanized steel sheet fabricated into tray, or may be hot-dip galvanized after fabrication. When galvanized tray is cut to length in the field, usually the cut surface will be painted with a zinc-rich compound to protect the metal from corrosion.
Fire safety concerns and solutions
Combustible cable jackets may catch on fire and cable fires can thus spread along a cable tray within a structure. This is easily prevented through the use of fire-retardant cable jackets, or fireproofing coatings applied to installed cables. Heavy coatings or long fire-stops may require adjustment of the cable current ratings, since such fireproofing measures may reduce the heat dissipation of installed cables.
Regular housecleaning is important for safety, as cable trays are often installed in hard to reach places. Combustible dust and clutter may accumulate if the trays are not routinely checked and kept clean.
Plastic and fibreglass reinforced plastic cable trays are combustible; the effect is mitigated through the use of fire retardants or fireproofing.
Ferrous cable trays expand with the increasing heat from accidental fire. This has been proven by the German Otto-Graf-Institut Test Report III.1-80999/Tei/tei "Supplementary Test On The Topic Of Mechanical Force Acting On Cable Penetration Firestop Systems During The Fire Test", dated 23 October 1984, to dislodge "soft" firestops, such as those made of fibrous insulations with rubber coatings. This also applies to any silicone foam seals, but is easily remedied through the use of firestop mortars of sufficient compression strength and thickness, as shown above. Also, some building codes mandate that penetrants such as cable trays are installed in such ways so as to avoid their contribution to the collapse of a firewall.
See also
References
- NEC, 2017, ISBN 978-1455912797
- ^ W.E. Steward and R.A. Beck, Modern Wiring Practice, Newnes, London, 2010 ISBN 978-1-85617-692-7, pages 266-272.
- Conduit or Cable Tray, the easy guide, Nov 27, 2017,http://www.t-trayusa.com/blog/2017/11/25/conduit-or-cable-tray-the-easy-guide Archived 2018-10-08 at the Wayback Machine. Retrieved 2017 Nov 29
- Wiring duct cable,https://bazaredakt.ir/full-introduction-to-alborz-duct/
- http://www.tnb.com/contractor/docs/cabletray_us_revised_lr.pdf Archived 2010-01-03 at the Wayback Machine One manufacturer's cable tray catalog, retrieved 2010 Aug 11.
- "Archived copy". Archived from the original on 2018-10-08. Retrieved 2017-11-29.
{{cite web}}: CS1 maint: archived copy as title (link) - Jones, Dean. "Cable Trays Make it Easy to Repair & Maintain Cables in Industrial Settings". Commercial Electricians Perth. Archived from the original on 2014-09-17. Retrieved 15 September 2014.