We can all agree that choosing the correct pathway for your electrical installation is crucial. This will be the structure, support, direction, protection and fastening of your electrical design, this article will give you some guidance when determining when to use Conduit or Cable Tray.

The Basics.

What is a Cable Tray and Conduit? This sounds like a silly question if you are immersed in this world, however the basic definition of a Cable Tray and Conduit can give us a pathway on when is the best idea to choose these over conduit or vise-versa.

Raceway: According to the National Electrical Code (NEC) a raceway refers to an enclosed channel of metal or nonmetallic materials designed expressly for holding wires, cable, or bus bars, with additional functions as permitted in this Code.

Cable Tray: According to the National Electrical Code (NEC),  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.

Conduit:  An electrical conduit is a tube used to protect and route electrical wiring in a building or structure. Electrical conduit may be made of metal, plastic or fiber, most conduit is rigid, but flexible conduit is used for some purposes.

Cable Tray Classifications

• Ladder Tray

The Ladder tray provides a solid side rail protection, system strength, smooth radius fittings, and a wide selection of materials and finishes. Ladder cable tray is generally used in applications with intermediate to long support spans

• Solid Bottom

This Cable Tray provides non-ventilated continuous support for delicate cables with added cable protection available in metallic and fiberglass. Also available are solid bottom metallic trays with solid metal covers for nonplenum-rated cable in environmental air areas. The Solid Bottom cable tray is generally used for minimal heat-generating electrical or telecommunication applications with short to intermediate support spans.

• Wire Mesh

This innovative type of Cable Tray provides job site or field-adaptable, it is used primarily for low-voltage wiring. Wire mesh tray generally is used for telecommunication and fiber optic applications. The Wire mesh tray systems are typically zinc plated steel wire mesh.

• Trough or Perforated Bottom

This type of tray provides moderate ventilation, trough cable tray is generally used for moderate heat generating applications with short to intermediate support spans.

• Channel

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.

Advantages of Cable Tray Systems

Cable tray advantages include wiring system design flexibility, simplicity, and lower installation cost, also Cable trays can typically adapt to complex configurations with a simple set of tools.

Cost: The cost for cable tray systems is not necessarily lower than that of conduit systems in all cases. However, compared to labor cost of conduit installation, cable trays present significant savings of up to 75% in some cases. (NECA, 2006)

In the case of cable tray, the ease of installation and the development of new innovative products that reduce the time and tools needed, coupled with lower materials costs, as well as a major reduction in cable-pulling costs, consistently results in double-digit savings when compared with similar steel conduit installations (Carazo,D. 2006)

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Conduit Advantages.

The most obvious reason for the pervasive use and popularity of conduit is the fact that it is an enclosed raceway offering outstanding protection to the shielded wiring or cable Grounding and bonding play a significant role in minimizing electromagnetic interference (EMI) by up to 95%, effectively shielding computers and sensitive electronic equipment from the electromagnetic interference (EMI) caused by power distribution systems.

It is important to consider that the coefficient of expansion for steel conduit/EMT is 6.5×10-6in./in./deg F. This is significant as it relates to whether or not expansion fittings would be required in a particular application thus outdoors installations might require expansion fittings which would also increase the installation cost and cost of materials.

Classification

According to NEC there are 3 different types of Conduit Rigid metal conduit (RMC) with the thickest wall, inside and outside zinc coated, Intermediate metal conduit (IMC) has a thinner wall with only an outside zinc coating for corrosion and Electrical metallic tubing (EMT) is the lightest weight steel conduit manufactured. EMT is made of galvanized steel and is unthreaded. 

What do I choose then?

At the end the type of Raceway you would need for an electrical installation will depend on different factors, among which the most important are:

• Environmental conditions
• Safety Requirements 
• Load 
• Corrosion Requirements 
• Space Available 
• Type of Cable Supported
• Budget 
• Expansion needs and design flexibility 

Sometimes the best option when you have particular questions about a specific type of installation, material or design  is to consult a professional and ask for advise. Most of the professional firms often offer consulting services for free.