Data Cable Tray Fill
Tray fill for communications bundles, with the tiers kept straight: the NEC Table 392.22(A), Column 1 allowable areas are code for cables the NEC regulates in tray; the 25%-initial / 40%-max / 6-inch-depth trio is TIA-569 comms practice; and the cable counts are computed from those plus the same verified cable diameters as the conduit fill chart.
Fill areas and 4-pair counts by tray width (ladder / ventilated)
| Tray width | NEC Col. 1 area (in²) | Cat6 UTP (0.24″) | Cat6A UTP (0.29″) |
|---|---|---|---|
| 6″ | 7.0 | 106 | 72 |
| 9″ | 10.5 | 159 | 109 |
| 12″ | 14.0 | 212 | 145 |
| 18″ | 21.0 | 318 | 218 |
| 24″ | 28.0 | 424 | 290 |
| 30″ | 35.0 | 530 | 363 |
| 36″ | 42.0 | 636 | 436 |
Depth is the limit people miss
The area math permits piles the cable can't survive: fill depth caps at 6 inches (and no more than half the rail height) because the bottom of a deep stack bears the weight of everything above it — crushed jackets and deformed pairs fail certification with no visible damage. High-power PoE tightens this further: big warm bundles are exactly what NEC 725.144 regulates, so a dense Type 4 tray needs the bundle ampacity chart alongside this one. For the conduit version of this math, see the Cat6 conduit fill chart; for the power-cable tray rules, the electrical trade's cable tray fill chart.
Common questions
What is the fill limit for data cable in cable tray?
Comms practice (TIA-569 tier): design to 25% calculated fill at initial installation, never exceed 40%, and cap the fill depth at 6 inches (or half the side-rail height) — cable stacked deeper stops counting and starts crushing. These are voluntary-standard/practice values; the NEC's Chapter 392 fill areas govern where the tray carries conductors the code regulates.
How many Cat6 cables fit in a 12-inch tray?
About 212 at the 40% practice fill with 2 inches of usable depth (Cat6A: 145). The counts scale linearly with width — roughly 18 Cat6 per inch of tray width — but remember the initial-install target is 25%: a tray "full" on day one has no room for the next renovation, and weight adds up fast at these counts.
Does the NEC limit communications cable in tray?
Differently than you'd expect: communications cables are largely exempt from the conductor-fill regime (NEC 800.110(B) exempts them from Chapter 9 raceway fill, and Chapter 8 stands alone), but Class 2/3 cables in tray and mixed trays fall under Article 392, and inspectors commonly apply the 392.22(A) areas as the reference. The clean answer on a real job: design to the TIA practice numbers — they are tighter than the NEC areas at these cable sizes — and nobody argues.
Run your whole job on the same numbers
These NORDIX tools are a taste of the full platform — bid pipeline, estimating, and job costing that carry your numbers from the first bid to the final invoice. Our team sets it up for your shop and walks you through your next real job.
Request access →