B-Line Systems Inc.
Highland, IL
As a cable tray product manager and as an active member of the Cable Tray Institute, I agree with the message in "Cable trays adapt to changing needs" (December 1995, page 14). However, some issues in the article need clarification:
Cable tray systems are mechanical support systems; raceways are enclosed channels designed to hold wires, cables or bus bars.
The National Electrical Code requires metallic cable trays to be grounded using bolted mechanical connectors or bonding jumpers. The cable management system pictured in the article only uses clamps.
A channel cable tray is commonly used for branch cabling or for smaller amounts of cables, and per the NEC, is 3, 4 and 6 inches wide.
If the cables in the tray are plenum-rated, they can be supported in ladder cable tray without covers. If the cables are not plenum-rated, the NEC allows them to be installed in solid-bottom metal cable tray with solid metal covers--and this system is still a cable tray system, not a raceway.
One of the drawbacks of a covered cable-tray system is that it makes cable additions and removals more difficult; however, some cable-tray systems--center-rail systems--could be covered and still offer flexibility.
The NEC Section 318-9, which addresses the allowable fill of particular cables in different types of cable trays, should be closely followed.