Cable Tray Types Overview
Cable trays are open cable management systems. NEC Article 392 recognizes these types:
- Ladder tray — Two side rails connected by rungs; best airflow, most common in industrial plants. Ideal for power cables ≥4 AWG.
- Solid-bottom tray — Full solid floor; provides physical protection and containment for oil drip environments. Requires ampacity derating.
- Perforated tray — Solid sides with perforated floor; compromise between ladder and solid-bottom. Common in commercial construction.
- Wire mesh tray — Lightweight, flexible, popular in data centers for low-voltage data cables.
- Channel tray — Small (4" or 6" wide) for small quantities of cables or instrument tubing.
Cable Duct/Wireway Overview
Cable duct (wireway, or cable trunk) is an enclosed sheet-metal or PVC raceway with a hinged or removable cover. NEC Article 376 covers metal wireways. Key differences:
- Enclosed on all six sides (three sides for cable tray)
- Conductors must be derated if fill exceeds 20% of cross-sectional area (NEC 376.22)
- Maximum 30 current-carrying conductors per section without derating
- Better dust and splash protection (NEMA 12 rated types available)
- Suitable for use in electrical rooms and panel areas where open trays may not be aesthetically acceptable
Ampacity Impact: The Most Misunderstood Difference
This is where engineers make costly mistakes. NEC 392.80 covers ampacity in cable trays. The key rule:
- Ladder or ventilated tray with 4 AWG or larger conductors: No ampacity derating required (cables treated as in free air)
- Solid-bottom or covered tray: Apply 95% of free-air ampacity for cables not in conduit
- Any tray type, cables ≤3 AWG: Apply 60% (conduit fill method) ampacity if bundled in groups of 4+
In contrast, cable duct/wireway with more than 30 current-carrying conductors requires derating even for large cables. For high-density power distribution, this makes open ladder tray significantly more efficient.
Head-to-Head Comparison
| Factor | Cable Tray | Cable Duct/Wireway |
|---|---|---|
| Heat dissipation | Excellent (open air) | Limited (enclosed) |
| Ampacity derating (power cables) | Minimal (ladder tray) | Significant beyond 30 conductors |
| Dust/moisture protection | Low | High (NEMA 12 option) |
| Future cable additions | Easy | Limited by fill rules |
| Material cost | Lower | Higher |
| Best for | Industrial, process plants | Electrical rooms, panels |
What Type of Cable Can Go in Cable Tray?
Not all cable types are listed for cable tray use. NEC 392.10 lists permitted cable types, including:
- Any cable listed and marked for cable tray use (TC — Tray Cable, UL 1277)
- Type MC cable (Metal Clad, listed for cable tray)
- Type MV cable (Medium Voltage)
- Conductors 4 AWG and larger in metallic conduit laid in cable tray
Standard THHN in cable tray is only permitted if it is installed in conduit that runs through the tray — THHN cannot be laid loose in cable tray without conduit.
The Right Cable for Cable Tray: Tray Cable (TC)
For factory-wiring the most economical and code-compliant solution for open cable tray is Tray Cable (Type TC, UL 1277). TC cable features:
- Multiple conductor configurations (2–37 conductors)
- Flame-retardant jacket rated for open tray installation
- Available with overall shielding for EMI-sensitive control circuits
- 600V rating standard; 1000V available for VFD circuits
- Oil-resistant jacket options for petrochemical and food processing
Need Tray Cable or Industrial Cable Direct from the Factory?
Shanghai Unicorn manufactures UL 1277 Type TC tray cable, MC cable, and VFD cable. Custom configurations, shielded options, and OEM runs. Factory-direct pricing with 24-hour quote turnaround.