Short answer: A cable tray is a support system, not a raceway. Article 392 lists which wiring methods may be installed in a tray (NEC 392.10), requires the tray to be installed as a complete system (NEC 392.18), limits how many cables you can put in it (NEC 392.22), and sets the conditions for using a metal tray as an equipment grounding conductor (NEC 392.60). For multiconductor power or lighting cables with conductors 4/0 AWG and larger in a ladder or ventilated trough tray, the sum of the cable diameters generally cannot exceed the inside width of the tray, laid in a single layer.
PSI lists raceways and cable trays among the topics in the Wiring Methods and Materials subject area of the Texas Journeyman exam: 10 scored NEC Knowledge questions and 2 scored Calculations questions. PSI does not say how many cover cable trays alone. The Texas Journeyman Practice Pack has 1,000 original questions and 10 timed mock exams in the real two-part format, with step-by-step solutions for every calculation. Try free practice questions without signing up. Get the full pack for US$39 with one payment.
Tsai Electro is an independent learning site. Not affiliated with TDLR, PSI or NFPA. We explain the ideas in our own words and do not reproduce NEC text. Check every rule and table value in your own 2026 NEC, follow the tray manufacturer’s instructions, and follow your supervisor and the local inspector.
What a cable tray is
A cable tray system is a unit or assembly of sections and fittings that forms a structural system to securely fasten or support cables and raceways. Unlike conduit, it does not enclose the conductors. That is why Article 392 controls what may go in it.
| Tray type | What it looks like | Where you see it |
|---|---|---|
| Ladder | Two side rails joined by rungs | Large power cables in plants and data centers |
| Ventilated trough | A bottom with openings, side rails | Control and power cables that need some support between rungs |
| Solid bottom | A bottom with no openings | Cables that need more protection, with reduced fill and ampacity |
| Channel | A narrow one-piece channel | A few small cables, drops to equipment |
| Wire mesh (basket) | Welded wire grid | Low-voltage and communications cables |
What can go in a tray
The article lists the wiring methods allowed in cable trays (NEC 392.10). The list includes many cable types, for example types MC, TC and ITC, along with raceways such as conduit. Some conditions apply only in industrial establishments with qualified maintenance and supervision, such as the use of single conductor cables of certain sizes. Check the list and its conditions before you lay any cable in a tray.
Two rules apprentices often miss:
- Not every cable is allowed. A cable must be one the list permits for the conditions of use.
- Mixing voltages. Cables rated over 1,000 V and cables rated 1,000 V or less generally cannot share the same tray unless they are separated by a solid fixed barrier or the higher-voltage cables are Type MC. Check the exact conditions in your 2026 NEC.
Install it as a complete system
The tray must be installed as a complete system (NEC 392.18). Changes in direction and elevation are made with compatible tray fittings per the manufacturer’s instructions, and where the tray is used for grounding, continuity and bonding across sections and fittings must be maintained. Trays must be accessible, exposed and supported so the cables are not damaged, with enough space above and around them to install and maintain cables. Cables are secured or supported where they leave the tray and where they run vertically. The support rules are in 392.30.
Fill for large multiconductor cables
How many cables fit depends on cable type, size and tray type (NEC 392.22). The simplest case to remember:
- Multiconductor power or lighting cables, all with conductors 4/0 AWG or larger, in a ladder or ventilated trough tray. The sum of the cable diameters cannot exceed the inside width of the tray, and the cables are laid in a single layer.
- Smaller cables, mixed sizes and solid bottom trays use area limits from the tables in 392.22, with separate columns and formulas. Read the column headings carefully before you calculate.
Worked example: how many large cables fit
A 24 in. inside-width ladder tray will carry multiconductor 4/0 AWG power cables only. Each cable has an outside diameter of 1.50 in. from the manufacturer’s data. How many cables can go in the tray?
- Rule. All cables are 4/0 AWG or larger and the tray is a ladder tray, so the sum of the diameters cannot exceed the inside width, in a single layer.
- Calculation. 24 in. ÷ 1.50 in. = 16 cables.
- Check. 16 × 1.50 in. = 24.0 in., which equals the inside width and does not exceed it. A 17th cable would bring the sum to 25.5 in., which is too much.
- Next steps on a real job. Check the cable ampacity rules for cables in trays in 392.80, the tray’s load rating, and any spacing the design calls for.
Bonding and using the tray as a grounding conductor
Metal cable trays can serve as equipment grounding conductors only where the conditions in Article 392 are met (NEC 392.60), generally in qualifying installations where the tray sections and fittings are identified for grounding and the cross-sectional area of the side rails meets the table in that section. Even where a tray is not used as a grounding conductor, metal trays that support electrical conductors must be bonded. Check 392.60 and Article 250 for the details.
Check yourself
- Is a cable tray a raceway? No. It is a support system, which is why the article limits what can be installed in it.
- For multiconductor 4/0 AWG and larger cables in a ladder tray, what limits the fill? The sum of the cable diameters cannot exceed the inside width, laid in a single layer.
- Can a metal cable tray always serve as an equipment grounding conductor? No. Only where the conditions in Article 392 are met.
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Find Article 392 tables faster on exam day
NFPA 70, National Electrical Code, 2026 Edition (softcover). Highlight the permitted wiring methods in 392.10, the fill rules and table columns in 392.22, and the grounding conditions in 392.60, and practice finding the right rule and its conditions before you choose an answer. The Texas exam is open book. PSI allows a soft-bound NEC with highlighting, underlining and notes made in advance. Loose-leaf, spiral-bound and ring-bound copies are not allowed, and only permanent index tabs made or supplied by the NEC publisher are permitted; homemade and third-party tabs are not.
FAQ
Is cable tray a raceway in the NEC?
No. A cable tray system is a structural support system for cables and raceways. Article 392 lists which wiring methods may be installed in it.
How do you calculate cable tray fill?
It depends on the cable type, size and tray type. For multiconductor cables with conductors 4/0 AWG and larger in ladder or ventilated trough tray, the sum of the cable diameters cannot exceed the inside width in a single layer. Smaller and mixed cables use the area tables in 392.22.
Can I put NM cable in a cable tray?
Do not assume it is. NM cable can go in a tray only where the cable type and the conditions of use are on the list of permitted wiring methods and the cable’s own article allows it. Check 392.10 and the cable’s own article in your 2026 NEC before you plan it.
Are cable trays on the Texas Journeyman exam?
PSI lists raceways and cable trays in the Wiring Methods and Materials subject area, which has 10 scored NEC Knowledge questions and 2 scored Calculations questions. PSI does not say how many cover cable trays alone.
Sources checked October 2026
- PSI Candidate Information Bulletin, Texas electrician examinations (updated September 15, 2026): https://test-takers.psiexams.com/api/content/bulletin/1682
- NFPA 70, National Electrical Code, 2026 Edition, Articles 250 and 392
