Cable Conduit vs. Cable Tray: Alternatives To Open Wiring
Two common alternatives to open wiring (types of an enclosed wiring system) are cable conduit and cable tray. Let's focus on which one to choose for your electrical application.
What is a Cable Tray?
A cable tray consists of one section or several sections that supports wiring. Cable trays are often used industrially and commercially, including in offices, malls, and restaurants. There are many types of cable trays depending on the structure, including ventilated tray, ladder tray, and channel tray.
What Cables are permitted in cable trays?
Types of cables that are allowed to be installed in cable trays can be found in article 392 of the NEC National Electric Code. The cables have to be fire-resistant, should have a top-notch tensile strength, and meet crush and impact testing requirements.
Common types of cables approved to use in the cable tray are type AC armored cables, communication cables, fire alarm cables, type MC metal clad cables, service entrance cables, and type UF underground feeder cables. Common building cables, such as THHN/THWN and RHH/RHW, can be used if they are specifically permitted for use in a tray.
Most often, tray cables designed specifically for cable trays are used in a tray. These include power-limited tray cable (PLTC), instrumentation tray cable (ITC), and others. Interestingly, cable conduits are also approved to run in trays.
What is a Cable Conduit?
A cable conduit is a tube typically made of metal and plastic that encloses electrical wire and cable and protects them. There are metal rigid conduit, non-metal (PVC) conduit, and flexible metal and non-metal conduit. Metal conduit is of either steel or aluminum. Many cables are rated for installation in conduit, with THHN being the most common one.
Are Conduit and Raceway The Same Thing?
Cable conduit is the subtype of raceway, perhaps the most popular one, but raceway is a more general term. In article 100 of the National Electrical Code NEC, a raceway is defined as an enclosed channel that holds wires and cables. Other types of raceway aside from conduit are wireway and tubing.
Wireways are non-circular raceways used when terminations and splicing are standard for an electrical application. They are an ideal choice when installation issues are possible. Wireways can be metallic and non-metallic. They are quite expensive compared to other types of closed wiring systems. For this reason, they are mainly used over short distances in industrial and commercial settings.
Tubing is the least heavy version of the cable raceway that can be bent and cut. It is typically made of aluminum or galvanized steel. Tubing is not recommended for use in corrosive environments as there is a lot of bureaucracy involved to approve such an application.
Conduit and Tray Compared: Pros and Cons
- The tray is usually cheaper compared to the conduit, thanks to the reduction in labor costs. Many types of cable trays, such as mesh trays, are specifically designed with the goal of saving costs in mind.
- Cable tray is more flexible than conduit and has a simpler and more approachable design.
- Cable trays are easier to maintain and inspect.
- The variety of cable tray systems is expanding, and new innovative design solutions are on the way.
- Conduits allow for grounding and bonding, which helps to control EMI. The conduit made of steel offers protection from electromagnetic interference without extra shielding.
- In case grounding is required, the conduit is to be used over the cable tray.
- Conduit protects wires better from all kinds of influence. This makes conduit a preferable choice in hazardous locations. Some types of conduit are corrosion resistant.
- Conduit can be used to bury cables in the ground.
