In addition to simply routing and protecting cables a cable tray system must provide protection to life and property against faults caused by electrical disturbances, lightening, failures which are part of the system, and failures of equipment that is connected to the system. These protections can be obtained through proper bonding and grounding. Article 250 of the National Electric Code (NEC) provides the minimum requirements for grounding and bonding. Article 392 provides guidance and minimum requirements specific to cable trays.

To understand these Code requirements adequately, one should always be familiar with defined terms related to the subject matter. Understanding how the defined terms are used within the Code will provide users an improved understanding of how the rules apply[……]

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National Electrical Code (NEC) Section 318-11 Ampacities of Cables, Rated 2000 Volts or Less, in Cable Trays. (b) Single Conductor Cables allows cables of identical construction and conductor material to be operated at different maximum ampacities depending on the physical placement of the cables in ladder or ventilated trough cable trays.

NEC Section 318-10 Number of Single Conductor Cables, Rated 2000 Volt or Less, in Cable Trays. (a) Ladder or Ventilated Trough Cable Trays. Doesn’t cover the width requirements of ladder or ventilated trough cable tray for all the types of installations that contain single conductor cables.

This is best exhibited by cable tray width calculations for three different examples of single conductor cables in ladder or ventilated trough cable tray that a[……]

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One of the most important choices when designing a cable tray system for corrosive or outdoor environments is the material. Steel cable tray with a Hot-Dip Galvanized after Fabrication (ASTM A123) finish has been used successfully for many years. Increasingly, however, aluminum is becoming the material of choice for cable tray systems. In these days of shrinking construction budgets, why would engineers, contractors, and end users choose aluminum cable tray, which typically has a slightly higher initial cost, over Hot-Dip galvanized steel cable tray? The answer lies in aluminum’s many advantages in design, installation, delivery, performance and total cost over the lifetime of the installation.

Design and Installation

Most people know of aluminum’s superior strength-to-weight ratio.[……]

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It is essential that the grounding of cable tray systems, including the cables in the tray systems, is inspected for compliance with the grounding requirements in the National Electrical Code (NEC) BEFORE the cabling in the tray is energized and BEFORE cable is installed. If cable is installed, then it is possible to energize the cable before a grounding inspection. It is also easier to do the cabletray grounding inspection if the tray system does not have cable installed.

Electrical grounding is essential for personal safety and protection against arcing that can occur in any part of the wiring system, motor enclosures, conduits, etc. The owner, engineering firm, or their designated representatives should provide approval of the inspection.

For safety reasons, the grounding should b[……]

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Cable tray wiring systems have excellent safety and dependability records. These excellent records are the result of cable tray’s unique features plus the proper design and installation of the cable tray wiring systems. The intent of this article is to review grounding practices for cable tray wiring systems. The Equipment Grounding Conductors are the most important conductors in the electrical systems. The Equipment Grounding Conductor is the electrical circuit’s safety conductor.

When designing a cable tray wiring system, the designer should evaluate the National Electrical Code’s (NEC) Equipment Grounding Conductor (EGC) options that are applicable for the project.

Evaluate the following Options:

1. Use the cable tray as the EGC. [The cable tray may only be used as an EGC in qual[……]

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The objective of this article to provide clear information as to the use of cable tray in those areas covered by Section 300-22 of the 1996 National Electrical Code.

Section 318-4 Uses Not Permitted states that “Cable tray systems shall not be used in environmental air spaces except as permitted in Section 300-22 to support wiring methods recognized for use in such spaces. The wiring methods allowed under Section 300-22 that utilize cable tray must follow the installation and safety requirements as covered in Section 318 – Cable Tray.”

Many of the misinterpretations about cable tray are due to the fact that those misinterpretations are made with the thought that cable tray is a raceway. It is not a raceway and it has never been a raceway in the National Electrical Code. Cable tray is[……]

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Cost is usually a major consideration in the selection of a wiring system. This article provides information as to where cable tray wiring system cost savings will occur; however, it is not the intent of this article to state that the selection of a wiring system should be based only on cost.

Early in the life of a project, the costs and the features of the applicable wiring methods should be evaluated to provide decision information for the selection of the best possible wiring method or methods for the project. The evaluations should include items that relate to cost, dependability, future changes, maintenance, safety, and space savings. Usually the evaluation will determine if a cable tray wiring system or a conduit wiring system is to be selected as the projects major wiring system.[……]

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It is not necessary to install bonding jumpers in parallel with the standard rigid aluminum or steel one-piece metallic bolted side rail splice plates that are the connections between the cable tray sections. Here, the use of bonding jumpers does not make a safety contribution to a properly installed cable tray system, and wastes both materials and labor.

For personnel and facility safety all the metallic electrical equipment enclosures and supports that may become energized in the event of an electrical fault must be bonded electrically back to the equipment connection for the system’s equipment grounding conductor cable tray wiring systems must comply with all the appropriate requirements of NEC Article 20 – Grounding Properly installed standard metallic splice plates provide the elec[……]

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Improperly secured covers on outdoor cable trays can cause a serious safety hazard in high winds. In the majority of cases, covers are not used on cable trays for technical or safety reasons, but due to the “raceway complex,” a feeling by specifiers that cables must be totally enclosed in metal. Quality tray cables have a life of 30 to 40 years without covers when exposed to the elements. For outdoor installations, the most desirable cable tray system is a ladder cable tray or a ventilated trough cable tray without covers. If covers are used they should be the ventilated type.

Cable tray wiring systems have a 30-year plus proven track record of safety and dependability. They are the best economic choice for commercial and industrial wiring systems.

Fig. 1. Wind Effect on Covered[……]

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