Often unheralded, cable trays play a vital role in tray cable installations throughout industrial, commercial, and residential projects. Just like the cables they hold, carrier trays are essential to safe electrical installations, but are not one-size-fits-all solutions.
It takes a lot of effort to ensure the tray cable fits the applications we need it for. We should show the same care when selecting cable trays, depending on the environment, cable, and location.
But what cable tray options are available, and how do you know what makes the most sense for your project?
As with anything electrical, the National Electrical Code (NEC) has rules tied to its use.
NEC Article 392.2 defines a cable tray system as “a unit or assembly of units or sections with associated fittings forming a rigid structural system used to securely fasten or support cables and raceways.” Other NEC codes cover the mounting used to install the carriers.
Basically, a cable tray is a support system for wires installed in an open area. Their job is to offer a place for the cables to go and protect them from debris, moisture, and other threats. Depending on the application, carriers can hold everything from tray cable and power limited tray cable (PLTC) to instrumentation wire and metal-clad armored cable.
Trays also hold data wires like fiber optics, communication, and fire alarm cables. To make this installation work, you’ll need to use a cable tray divider to separate power from data cables to stay UL compliant.
Typically, manufacturers make carrier trays out of lightweight and strong aluminum. But when the situation calls for it, you can also find galvanized steel, stainless steel, fiber-reinforced plastic (FRP), or fiberglass trays.
Metal is durable and cost-effective but corrodes in certain situations. To reduce corrosion risk, manufacturers may coat trays with either PVC or use an electro-zinc process to galvanize the metal.
Despite potential corrosion, metal cable trays protect wire well and hold plenty of weight without compromising. Metal trays, like aluminum, steel, and coated steel, also work for equipment grounding, per OSHA 1910.305(a)(3)(iii).
Meanwhile, fiberglass trays are unique because they offer several other benefits. Unlike metal, fiberglass will not rust and is lightweight, durable, non-magnetic, and fire-retardant. It also excels in marine applications, where sea salt could eat metal, and in areas where corrosion is a risk.
This might sound trivial, but just because a tray holds and protects cable doesn’t make it a raceway.
Raceways are enclosures designed to protect cables but must comply with different rules. Unlike trays featuring openings and venting, raceways encompass the wires running through them. Raceways also follow fill capacity and conductor count rules outlined by the NEC.
Cable trays, on the other hand, provide some protection but have open areas where moisture, dust, and other stuff can accumulate. Trays are also easier to work with than conduit because cables are more accessible for repair or removal.
Though trays offer less protection than conduit, they’re easier to manage and cleanly organize wires. They also have much better ventilation and heat dissipation than fully closed conduits.
Although you can use cable trays anywhere wires need protection, a few common locations stick out, including:
Generally, cable trays ensure accidental contact with people and machines is avoided. Trays also work where chemicals, moisture, dust, and other concerns could cause issues.
Depending on venting, weight limits, cost, environment, and moisture/heat dissipation, the type of tray needed may change.
Beyond the different cable tray types, some manufacturers provide additional services, like powder coating, to help workers identify runs in crowded areas.
Having the right tool for the job isn’t helpful when you’re not using it correctly. Learning to handle carrier trays can save you time, money, and labor costs over a project’s lifespan.
Know how the cable trays work before installation, including how they move or bend. With that said, don’t move or bend trays without using approved pieces! Consult NEC Article 392.5(E) if you have questions about which parts are approved for changing direction and altering grounding paths.
NEC guidelines even regulate the cables and zip ties used to secure wires in the tray through UL 62275 and NEC Article 392.30(B).
When space is tight, proper cable management sometimes means installing data and power cables in the same cable tray.
Power cables emit electromagnetic interference (EMI) during use, potentially interfering with more delicate data cable types. Dividers allow power and data cables, like telecom, instrument, and signal wires, to rest in the same tray while limiting EMI.
Tray dividers also work for separating high-voltage cables (>600V) from lower-voltage ones when sharing the same tray.
The last thing any installer wants is to damage the wire during installation. To avoid those situations, the NEC has several rules to ensure installations are safe and secure, including Article 392.100.
These guidelines cover everything from tray rigidity and smooth edges to corrosion protection, fitting, and even flame resistance.
Fill amounts, spacing, and weight limits are all necessary information, especially to avoid heat dissipation.
When multiple wires are in the tray, consider using a carrier with more tray width to accommodate the additional cabling or derate the ampacity of the cables to reduce heat buildup. In high-risk areas, flame-retardant cabling can offer more protection in the case of a fire.
And as with any installation, what we do today can impact future decisions. The goal for every installation is to be as safe as possible while ensuring there is room for future expansion.
In every case, keep the environment in mind and know what dangers lurk out of view. Not following the rules can turn a minor issue into a catastrophic problem without anyone realizing it.
Cable trays are a critical part of any tray cable installation. While installing them seems easy enough, workers should know the rules and regulations.
Not knowing the rules can have massive consequences, ranging from overheated cables and ground faults to reduced efficiency and shorter cable lifespans. At the least, you could set yourself up for several code violations, resulting in lost time and wasted labor.
Like any installation, always anticipate the consequences. Use the correct tray for the job, don’t jam more wires into the system than it can handle, and keep an eye on the NEC guidebook.
