U.S. Department of Labor

Occupational Safety and Health Administration

Directorate of Technical Support & Emergency Management

Office of Technical Programs and Coordination Activities

SHIB 01-16-2008

Safety and Health Information Bulletin

Safely Installing, Maintaining and Inspecting Cable Trays

This Safety and Health Information Bulletin (SHIB) is

not a standard or regulation, and it creates no new

legal obligations. The Bulletin is advisory in nature,

informational in content, and is intended to assist

employers in providing a safe and healthful

workplace. The Occupational Safety and Health Act

requires employers to comply with safety and health

standards promulgated by OSHA or by a state with

an OSHA-approved state plan. In addition, pursuant

to Section 5(a)(1), the General Duty Clause of the

Act, employers must provide their employees with a

workplace free from recognized hazards likely to

cause death or serious physical harm. Employers can

be cited for violating the General Duty Clause if there

is a recognized hazard and they do not take

reasonable steps to prevent or abate the hazard.

However, failure to implement any recommendations

in this SHIB is not, in itself, a violation of the General

Duty Clause. Citations can only be based on

standards, regulations, and the General Duty Clause.

Purpose

The purpose of this Safety and Health Information

Bulletin is to:

Review the proper methods for safely

installing, maintaining and inspecting electrical

cable trays;

Provide information regarding the hazards of

overloaded cable trays;

Identify specific Occupational Safety and

Health Administration (OSHA) regulatory

requirements and National Electrical Code®

(NEC) guidance that address the proper

installation and maintenance of cable trays;

Recognize electrical cable tray misuse that

can lead to electric shock and arc-flash/blast

events and fires caused by overheating.

OSHA Regulations and Industry Consensus

Standards that Apply to Cable Trays

The use and installation of cable trays is covered by

legally enforceable OSHA regulations in 29 CFR

1910.305(a)(3), or comparable standards

promulgated by States operating OSHA-approved

State plans. In addition, this document contains

several references to provisions of the National

Electric Code (NEC), which is published by the

National Fire Protection Association (NFPA). The

2005 edition of NEC is listed as a reference in

Appendix A – “Reference Documents” of OSHA

Subpart S, Electrical (1910.301 through 1910.399).

While these references provide nonmandatory

information that can be helpful in understanding and

complying with Subpart S, compliance with the

referenced provisions of the NEC is not required and

is not a substitute for compliance with any applicable

OSHA standards.

Although the recently promulgated electrical

standards for general industry at 29 CFR 1910

Subpart S (72 FR 7136—7221, February 14, 2007)

are based on the 2002 edition of the NEC, OSHA

has not conducted rulemaking to adopt all of the

requirements of the NEC (or subsequent revisions)

and, therefore, cannot enforce those requirements.

However, industry consensus standards such as the

NEC and others referenced throughout this Bulletin

can be used by employers as guidance for conducting

hazard analyses and selecting effective control

measures.

The National Electrical Manufacturers Association

(NEMA) also publishes three consensus standards

that apply to the proper manufacture and installation

of cable trays: ANSI/NEMA-VE 1-1998, Metal

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Cable Tray Systems; NEMA-VE 2-1996, Metal

Cable Tray Installation Guidelines; and NEMA-FG1998, Nonmetallic Cable Tray Systems.

Cable Trays

According to OSHA 1910.399, a cable tray system 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. Cable tray systems include ladders,

troughs, channels, solid bottom trays, and other similar

structures.” Cable trays are not raceways, but they

are treated as a structural component of a facility’s

electrical system. Cable trays are a part of a planned

cable management system to support, route, protect

and provide a pathway for cable systems. Cable trays

support cables across open spans in the same way

that roadway bridges support traffic.

Cable trays can provide a safe component of a power,

low voltage control, data or telecommunications wiring

distribution system. Cables in trays can be easy to

mark, find, and remove. Their flexibility makes cable

trays a good choice for installation situations that

require upgrading, reconfiguring, or relocation.

Cable trays are available in a number of different

configurations, including ladder, ventilated trough,

ventilated channel, solid bottom, wire mesh, single rail

and other configurations. They come in a wide variety

of shapes and sizes, with a host of hanging options that

are able to meet almost any installation need. Cable

trays are manufactured of steel, stainless steel,

aluminum and fiber reinforced plastic (FRP). They

also are available with special finishes including

polyvinylchloride (PVC) coated and galvanized finish.

A significant portion of cable trays used in industry

today are aluminum. Aluminum, steel and coated-steel

cable trays, all being metallic, may be used as

equipment grounding conductors in accordance with

OSHA 1910.305(a)(3)(iii). This requirement is

mirrored by the guidance provided by NEC Section

392.3(C). Depending on the need, covers and

ventilated louvers or slats are available for all trays.

Covers physically protect the cables as well as

shielding the cable jackets from the sun’s ultraviolet

radiation when used outdoors. Suitable guards or

covers must be installed to a minimum height of 2.5m

(8 ft.) above grade such as where cable trays are

exposed to physical damage from vehicular traffic.

Ventilated louvers also protect the cables and

facilitate cooling by allowing natural convection (heat

dissipation) to occur.

Cable Tray Use

Cable trays can be used in a variety of settings.

Cable trays can be rated for outdoors, indoors,

corrosive and classified hazardous locations, and

areas with high electrical noise and vibration. As

with any electrical equipment, cable trays and the

wiring contained in the trays must be listed, labeled

or otherwise approved, pursuant to the requirements

of 29 CFR § 1910.303(a). The National Electrical

Manufacturers Association (NEMA) Standard VE

1-2002 provides guidance for metal cable trays and

associated fittings designed for use in accordance

with the rules of the NEC. NEMA Standard VE 2-

2006 addresses shipping, handling, storing, and

installing cable tray systems; it also provides

information on cable tray maintenance and system

modification. Compliance with these standards helps

to ensure safe loading and the electrical continuity of

cable tray systems.

Cable trays may be designed to cross through

partitions and walls, as well as go vertically through

platforms and floors.

However, where cable trays (and the conductors

and cables they contain) pass through fire-rated

partitions, walls and floors, appropriate fire-stops

Figure 1. Ladder cable tray, ventilated cable tray,

solid-trough cable tray.
3

should be provided in accordance with NEC Section

300.21 to prevent the spread of a fire or the byproducts of combustion. Typically, specific building

codes should be consulted and the design and

oversight should be done by a qualified engineer.

Use of cable trays is popular in hazardous locations

where concentrations of flammable or combustible

gases, vapors and dusts exist. However, the improper

use of cable trays in these environments could result in

an explosion. 29 CFR § 1910.305(a)(3)(iv) requires

that cable trays in hazardous (classified) locations

contain only the cable types permitted in such

locations (see 1910.307 for details on hazardous

(classified) locations). In addition, the NEC also

contains specific requirements for wiring in hazardous

or classified environments. For example, NEC

Section 392.3(D) states that cable trays in hazardous

locations should contain only the wiring permitted in

specific sections of Chapter 500 (Sections 501.10,

502.10, 503.10, 504.20 and 505.15).

Proper Loading of Cable Trays

Since cable trays come in a wide variety of sizes, they

can be designed to accommodate a wide range of

loading configurations. Because of their flexibility,

cable trays are especially subject to overloading. Safe

and permissible loading of cable trays is governed by

three criteria: manufacturer-specified weight

restrictions; limitations of cable fill because of crosssectional area limitations; and conductor spacing

Figure 2. Outdoor metal clad cable in cable tray.

Figure 3. Electrical wires in multiple cable trays.

requirements. The appropriate size and number of

cable trays for an installation depends on the number

and size of conductors included and the allowable fill

area specified in the guidance provided by the NEC.

Because cable trays offer flexibility for expansion and

changes, engineers and designers should design and

size cable tray systems to anticipate both current and

future needs.

Load and Support Requirements

29 CFR § 1910.303(b)(8) requires the appropriate

mounting and cooling of electrical equipment.

Additionally, guidance provided in NEC Section

392.6(C) states, in part, that cable trays shoul be

supported at intervals in accordance with the

installation instructions. This straightforward approach

is corroborated in 29 CFR § 1910.303(b)(2), which

states that “listed or labeled equipment shall be used

or installed in accordance with any instructions

included in the listing or labeling,” and guidance

provided by NEC Section 110.3(B). The type and

number of cable trays, and the support required to

handle loads must take into account several factors,

including, but not limited to, environmental or weather

factors; the weight of the cable tray; current and future

cable needs; electromagnetic forces; and any

accessories installed. Manufacturers of cable tray

systems provide a wide range of parts and typical

support methods, as well as detailed installation guides

and tables for appropriate supports and support
4

spacing for cable trays. However, engineering

calculations are often required to determine where to

place supports so that the designed cable tray system

provides the proper strength.

Concurrently, NEC392.6(J) permits cable tray

systems to externally support raceways, cables and

boxes, and conduit bodies as covered by Section

314.1, provided that the cable tray is listed and

designed for the application. Support for the

equipment also must be in accord with the appropriate

NEC article. This permission does not extend to

other non-electrical equipment, such as water pipes,

sprinklers, and gas pipes. In addition, cable tray

supports should also take into account dynamic loads

(e.g., loads caused by the motion of the cable tray

system and its contents) and lateral stressors. Cable

tray systems need not be absolutely rigid; most

systems are designed with about a 1/200 spandeflection ratio (i.e., 1.2 inches in a 20-foot span)

when fully loaded.

Wiring Fill and Spacing Requirements

In industrial establishments, where the conditions of

maintenance and supervision assure that only qualified

persons will service the installation, OSHA

1910.305(a)(3)(ii) defines the wiring methods that

may be installed in cable trays. Cable tray fill is

addressed in NEC Sections 392.8, 392.9, 392.10,

and 392.12. The type of cable tray (e.g., solid,

ventilated), ampacity (current-carrying limit)

requirements, and the type and voltage rating of cable

used determines the allowable fill for each cable tray.

Ventilated cable trays provide for the greatest

allowable fill due to increased airflow. A generic

guideline developed by the Cable Tray Institute

indicates that cable trays should not be filled in excess

of 40-50% of the inside area of the tray or of the

tray’s maximum weight based on the cable tray

specifications. However, the NEC provides more

detailed requirements for cable tray fill (e.g., single

conductors sized 1/0 through 4/0 used in ladder or

ventilated cable trays must be installed in a single layer

and where multi-conductor cable is used 4/0 and

larger conductors must be installed in a single layer

and the sum of the diameters of the cables must not

exceed the width of the cable tray). In making cable

tray fill determinations, the best strategy is to review

and follow the requirements of the NEC and the

manufacturer’s installation guides to determine the

appropriate fill when installing cable in cable trays.

The ampacity (current-carrying rating) for conductors

and cables in cable trays provided in NEC Sections

392.11 and 392.13 is based on compliance with the

NEC cable tray fill requirements.

Importance of Supports and Allowable Fill

Overfilling cable trays can lead to a number of serious

hazards. The weight of the cables inside the cable tray

may pose a hazard. All cable trays and their

associated supports are rated for a specific maximum

weight, based partly on the allowable fill area and the

spacing of the cable tray supports. Overloading cable

trays can lead to a breakdown of the tray, its

connecting points, and/or supports, causing hazards to

persons underneath the cable tray and even leading to

possible electric shock and arc-flash/blast events from

component failure that occurs when the cables are

suddenly no longer supported. Paragraph (b)(1) of 29

CFR 1910.303 requires that equipment shall be free

from recognized hazards that are likely to cause death

or serious physical harm to employees. Some of the

tests for suitability and use are mechanical strength and

durability (1910.303(b)(1)(ii)), heating effects under

all conditions of use (1910.303(b)(1)(v)), and arcing

effects (1910.303(b)(1)(vi)).

Paragraphs (b)(8)(ii) and (b)(8)(iii) of 29 CFR

1910.303 contain requirements for the cooling of

electrical equipment. Avoiding heat buildup is another

important issue. The NEC requirements for cable tray

fill address heat build-up in conductors while current is

flowing. When cable trays are overloaded, excessive

heat builds up in and around live conductors, which

can cause the insulation to break down and create

potential shock hazards or fires. Fires can occur

either in cable trays (which may provide a fire path) or

in combustible materials near cable trays.

Furthermore, the improper use of flexible cord within

cable trays could lead to the spread of toxic vapors if

a fire were to occur.
5

Types of Conductors to Use

Any wiring method used in cable trays must be

“acceptable” as defined in OSHA 1910.399. In other

words, the wiring method used must be listed by a

nationally recognized testing laboratory (NRTL) as

suitable for use in cable trays and in the environment in

which it is installed. 29 CFR § 1910.305(a)(3)(i) and

NEC Table 392.3(A) provide corresponding lists of

wiring methods permitted in cable tray systems.

Additionally, 29 CFR § 1910.305(a)(3)(i)(b) and

NEC Section 392.3(B) allow other specific

conductors in industrial establishments where

maintenance and supervision assure that only qualified

persons will service the cable tray systems.

Mixing of cable types and voltages is permitted in

cable trays provided that some specific requirements

are met. For example, NEC Section 392.6(F)

permits cables rated to carry over 600V to be

installed with cables rated 600V or less, provided that

the cable rated over 600V is Type MC, or if a solid

fixed barrier of material compatible with the cable tray

is installed to separate the voltage levels. Installing

barriers between power and control cables is a

recommended practice, regardless of the ratings and

voltages of the cables in question.

It is important to note that although NEC Table

392.3(A) states that “other factory-assembled, multiconductor control, signal, or power cables that are

specifically approved for installation in cable trays”

may be used in cable trays, flexible cords and cables

are not approved for use in cable trays (29 CFR §

1910.305(g) - Flexible cords and cables, and NEC

Article 400). There are several reasons for this. First,

both OSHA and the NEC prohibit the use of flexible

cord as a replacement for the fixed wiring of a

building. Since wiring in cable trays is considered a

fixed or permanent wiring method by both OSHA and

the NEC, flexible cords are prohibited from being

used in cable trays (see NEC Article 400.4 for a list of

prohibited flexible cords). Secondly, flexible cord

insulation can break down and become brittle over

time which can result in electrical shorts, shock

hazards, and fires releasing toxic smoke.

Additionally, flexible cords and cables might not be

rigid enough to span the openings in ladder and

ventilated-type cable trays. Furthermore, the

conductor insulation might not withstand the load of

stacked cables.

Securing Cables within Cable Trays

There are many reasons for securing cables within

cable trays. Securing cables will maintain proper

spacing between cables, keep cables in the trays, and

confine the cables to specific locations within trays.

Those designing and installing the system must

determine the distances between fastenings in cable

trays. While the weight of the cable itself keeps it in

the tray in horizontal runs, the recommended practice

is to tie all cables down so that the cables are not

knocked out or “whipped” during abnormal or fault

current conditions. When cables are not installed in

horizontal runs, guidance presented by NEC 392.8(B)

indicates that said cables should be securely fastened

to transverse (crosswise) members. Smaller diameter

cables might need to be lashed or tied to the cable

tray more frequently than the stiff large diameter

cables to prevent them from hanging away from the

cable tray. Support is also required where cables are

routed from one cable tray to another or where cables

enter raceways or other enclosures (see OSHA

1910.305(a)).

Certain cable installations, such as in higher ambient

temperatures, might require the spacing between

adjacent cables to be increased to not less than one

cable diameter between cables pursuant to NEC

Section 392.11. Generally, multiconductor cables do

not need to be spaced.

Cable ties should be appropriate for the conditions in

which they are used. Factors such as moisture

resistance, ultraviolet resistance, extremely high or low

temperatures, chemical resistance, flammability, lowsmoke characteristics, tensile strength, and length are

important to consider. In all cases, persons installing

or inspecting cable tray installations should refer to the

manufacturer’s instructions and specific NEC articles

for the proper wiring support method to be used.
6

Proper Grounding and Bonding

Grounding and bonding help to prevent electrocutions

and arcing by facilitating the operation of over current

devices and preventing exposed non-current-carrying

metal parts and enclosures from being energized.

Proper grounding and bonding is done before the

cable is installed and must be tested before the cables

are energized.

Grounding and bonding are often associated together,

although, in reality, they represent two different

concepts. Bonding is the permanent joining of

metallic parts to form an electrically conductive path.

Equipment grounding is the connection of noncurrent-carrying metal parts of equipment, raceways,

and other enclosures to the system’s grounded

conductor, the grounding electrode conductor, or

both, at the service equipment or at the source of a

separately derived system. Both grounding and

bonding are done to ensure electrical continuity and

also to assure the capacity to safely conduct any

current likely to be imposed upon those non-currentcarrying metal parts, like cable trays.

Metallic cable tray systems used to support electrical

conductors must be grounded and electrically

continuous, and effectively bonded as required for

conductor enclosures (specified by 29 CFR §§

1910.304(g)(5), 1910.304(g)(6) and mirrored by the

guidance provided by NEC Section 250.96). If the

employer is following NEC guidelines, cable trays

may be used as equipment grounding conductors

provided that continuous maintenance and supervision

ensure that qualified persons will service the installed

cable tray system and that the provisions of NEC

Section 392.7 are met (i.e., cable trays are marked

for use as equipment grounding conductors and

minimum cross-sectional areas meet, and are marked

as meeting, the requirements of Table 392.7(B)). If

the cable tray system does not meet the marking

requirements of NEC Section 392.7, it also would not

meet OSHA’s suitablilty requirement in

1910.303(b)(1). Therefore it cannot be used as the

equipment grounding conductor for branch or feeder

circuits unless a single equipment grounding conductor

is installed in the tray and listed bonding connectors or

jumpers are used to effectively bond the cable tray

sections together to ensure electrical continuity.

Grounding of cable trays is so important that it has

become the industry practice to use grounding

conductors in cable trays for added reliability,

regardless of how the tray is listed and marked. It is

also recommended that cable trays be bonded to

building steel or earth every 60 feet in order to reduce

noise in the system. Where a cable tray includes only

multiconductor cables, there is generally no need to

use the tray as an equipment grounding conductor

because each multiconductor cable should have

integral equipment grounding conductor. Cable trays,

however, should be bonded in accordance with NEC

Section 250.96(A). Bonding jumpers on cable trays

are important to maintain the electrical continuity and

the ability to safely carry any fault current likely to be

imposed (in accordance with NEC Section 250.96).

As cable trays are typically fastened using direct

bolted connections, which provide bonding, bonding

jumpers are only required at adjustable splice plates,

expansion plates and non-continuous sections of trays.

However, as with the use of equipment grounding

conductors, industry practice is to use bonding

jumpers at all splice points to ensure continuity.

Figure 5. Grounding and bonding hardware.

Figure 4. Cable ties.
7

Required continuity applies to all enclosures and

utilization equipment and to cable dropouts from the

tray system to enclosures. If channel dropouts or

conduit-to-cable tray adapters listed for grounding are

not used, grounding and bonding must be provided by

grounding conductors in the cable or by bonding

jumpers.

Recognizing Overloaded Trays

Recognizing overloaded cable trays is not difficult. If

visual observation of the cable tray reveals that the

cable tray is nearly full or overflowing with cables,

then the installation does not meet the guidance

provided by the NEC. Cable tray fill is addressed in

the 2005 edition of NEC Sections 392.8, 392.9,

392.10, and 392.12. The number of single

conductors or multiconductor cables that are

permitted in a cable tray as indicated by the NEC

range from a single layer to a fill value that might

represent 50% of the cross-sectional area of the

interior space within the cable tray. This is an extreme

limit and the cable tray will appear to be over half full

due to voids between the cables or conductors.

Another consideration for cable tray fill is not to

overload the cable tray or its support system beyond

their ratings.

In any case, the best strategy is to review and follow

the rules set out in the NEC and the manufacturer’s

installation guides when installing cables in cable trays.

Solutions for Overloaded Cable Trays

If cable trays are overloaded because of poor design

and/or installation, the solution is to add additional

able trays in accordance with guidance provided by

the NEC. Another effective strategy for preventing

overfill is to review and follow the manufacturer’s

installation guides when installing cables in cable trays.

However, one of the major causes of overloaded

cable trays is abandoned conductors and cables for

circuits no longer in use, which often are not removed

from the cable tray when replacement or additional

cables are added. The solution in this instance is to

remove abandoned cable when they are no longer

necessary.

In fact, Section 590.3(D) and various sections in

Chapter 8 of the NEC specifically indicate that

abandoned communication cable and temporary

wiring installed within cable trays should be removed

upon the completion of projects.

Preventing Damage to Cables and Conductors

The cables and conductors approved for use in cable

trays are required to be insulated. However, while the

insulation of the conductors does provide some

protection, it is important to use measures to prevent

damage to the insulation when working around

energized conductors or cables so as not to damage

the insulation. If the work the employee is performing,

such as adding boxes or other approved electrical

equipment using screws or bolts, drilling into the cable

tray, and pulling or dragging cables or conductors

across each other, could damage the insulation, then

the wiring must be de-energized when attaching boxes

or other approved electrical equipment to cable trays.

In general, 29 CFR 1910.333(a)(1) requires that live

parts to which an employee may be exposed shall be

deenergized before an employee works on or near

them.

Figure 6. Overloaded Cable Tray.
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Conclusion

Cable trays can provide a safe component of a wiring

distribution system. However, if not designed and

installed properly, wiring inside cable trays may pose

hazards such as fire, electric shock and arc-flash blast

events. During the maintenance, installation and

inspection of cable trays, the following concerns

should be taken into consideration.

 • Cable trays, and the conductors and cable

they contain, must be listed or labeled by a

NRTL as suitable in the environment in which

they are installed.

 • Where cable trays pass through fire-rated

partitions, walls and floors, appropriate fire

stops should be provided in accordance with

guidance provided by NEC Section 300.21 to

prevent the spread of a fire or the by-products

of combustion.

 • Cable trays in hazardous locations must only

contain the wiring permitted in such locations.

 • Cable trays must be properly supported in

accordance with the installation instructions.

Overloading cable trays can lead to a

breakdown of the tray, its connecting points

and/or supports, causing hazards to persons

underneath the cable tray and even leading to

possible electric shock and arc-flash/blast

events from component failure when the

cables are suddenly no longer supported.

 • When cable trays are overfilled, excessive

heat build-up in and around live conductors

can cause the insulation to break down,

leading to potential shock hazards or fires.

• The fill values for cable trays specified in the

2005 NEC range from a single layer to

roughly a 50% fill of the cross-sectional area

of the cable tray.

• When cable trays are overfilled beyond the fill

criteria established by the NEC, add another

cable tray system above, below, or next to the

overfilled tray. Allow enough working space

around the added cable tray.

• Grounding of cable tray systems is essential

for personal safety and protection against

arcing that can occur anywhere in the wiring

system. Proper grounding must be done

before cables are installed and tested before

cables are energized.

• Abandoned cables within cable trays should

be removed.

• Work on cable tray installations may expose

employees to live parts. According to 29

CFR 1910.333(a)(1) deenergization of live

parts to which an employee may be exposed

is required before employees begin work on

or near them.
For more information

National Electrical Code® (2005) Article 392 (See

also NEC® Handbook).

OSHA Electrical Standard on Cable Trays, 29 CFR

1910.305(a)(3).

OSHA Fact Sheet - Electrical Safety Hazards of

Overloading Standard Cable Trays

(http://www.osha.gov/Publications/cable_trays_fs.pdf)

Cable Tray Institute (http://www.cabletrays.com)

Cable Tray Manufacturers:

Cabofil(http://www.cablofil.com)

Chalfant (http://www.chalfantcabletray.com)

Cooper (http://www.b-line.com)

Enduro Systems, Inc.(http://

www.endurocomposites.com)

GS Metals(http://www.gsmetals.com)

MPHusky (http://www.mphusky.com)