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 support wiring. Cable trays are often used industrially and commercially, including in offices, malls, and restaurants. There are many cable trays depending on the structure, including ventilated, ladder, and channel trays.
What cables are permitted in cable trays?
The types of cables allowed to be installed in cable trays can be found in Article 392 of the NEC National Electric Code. The cables must be fire-resistant, have top-notch tensile strength, and meet crush and impact testing requirements.
Common types of cables are approved for use in the cable tray under NEC 392. 3 are type AC armoured cables, communication cables, fiber optic cables, fire alarm cables, type MC metal-clad cables, service entrance cables, non-metallic sheathed cables, MI metal sheathed 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 if they have other ratings specified in NEC 392.3.
Most often, tray cables designed specifically for cable trays are used in a tray. These include power-limited tray cables (PLTC) and instrumentation trays (ITC). Interestingly, cable conduits are also approved to run in trays. These include electrical metallic and non-metallic tubing, flexible and intermediate metal conduit, and flexible non-metal conduit.
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/THWN 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 raceways aside from conduits are wireways 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, and it can be bent and cut. It is typically made of aluminium 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 than the conduit, thanks to the reduced labour costs. Many types of cable trays, such as mesh trays, are specifically designed to save costs.
- Cable tray is more flexible than conduit and has a simpler and more approachable design.
- Cable trays are easier to maintain and inspect because they provide easy cable access.
- The variety of cable tray systems is expanding, and new innovative design solutions are on the way.
- The open structure of trays allows for better heat dissipation, reducing the risk of overheating in power cables.
- Trays offer less physical protection compared to conduits; cables are more exposed to environmental hazards, such as dust, moisture, and chemical vapors.
- Trays are noticeable and visually unappealing in environments where this might pose a concern.
- Conduit provides excellent protection from physical and environmental damage. Cables used in conduit should generally be weather and water-resistant.
- Conduits allow for grounding and bonding, which helps to control EMI. The conduit made of steel offers protection from electromagnetic interference without extra shielding.
- If grounding is required, the conduit will 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 also offers superior fire protection.
- Conduit can be used to bury cables in the ground.
Conduit vs. Tray Use Cases
- The cable tray can be picked over conduit if the conduit is too expensive for an electrical project.
- A cable tray is best if frequent maintenance is required.
- For more hazardous environments, cable trays are a better choice.
- The best use cases of cable trays are industrial settings, data centres, and offices that call for access to cables for maintenance.
- Conduits are mostly used in residential and commercial buildings where additional protection is required.
- They are also used in environments with harsh conditions, such as underground or outdoor applications where exposure to moisture or chemicals is a concern.
NNC offers all kinds of conduit and trays, and the cables approved for use in these enclosed wiring systems. These include THHN/THWN-2, XHHW-2, XLP USE 2, UF-B, NM-B, SER, SEU for conduit, and all cables permitted under NEC Article 392 for tray.
