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TABLE 1 – NEMA CLASSES AND LOAD RATINGS
NEMA Standard VE-1 8A-12A 12B 12C 16A A6B 16C 20A 20B 20C
Load/Span Class
50 lb./ft 70 lb./ft 100 lb./ft 50 lb./ft 75 lb./ft 100 lb./ft 50 lb./ft 75 lb./ft 100 lb./ft
NEMA Load/Span
12' span 12' span 12' span 16' span 16' span 16' span 20' span 20' span 20' span
Selecting the Tray – Key Considerations
The first step is to determine what type of system is best for the intended application.
Weight capacity and cable volume must be calculated to specify the correct tray criteria,
and trays requiring greater span distances will require a greater cross-sectional area
for the side rails. This is classified and defined in the VE-1 standards. See Table 1 for an
overview of NEMA classes and load ratings.
Knowing the type of cable and the environment in which it will be installed will determine
the type of cable tray you need.
LADDER TRAY
A ladder tray is a prefabricated metal structure consisting of two side rails
connected by individual transverse members or rungs. Used in most cable tray
system installations, ladder trays provide maximum ventilation for cabling. Ladder
trays are commonly used in exposed areas like industrial facilities or data centers.
VENTILATED TROF
A prefabricated metal structure with clear openings up to 4". Trof cable trays are
the best choice for smaller cables. Ventilated trofs offer enhanced airflow while
eliminating cable sagging. The vent holes may be bushed with a grommet for
dropping out communication cables.
SOLID TROF
The bottoms of solid trofs have no openings within the cable bearing surface. Solid
bottom cable trays eliminate cable sagging and offer the most protection for cables.
A trof is usually optimal for any size cable. The bottom design also offers safety and
security from unauthorized personnel.
CHANNEL
A channel tray consists of a one-piece ventilated or solid bottom channel section up
to 6” wide. Offered in ventilated or solid bottom, channel systems with pre-punched
holes allow the secure attachment of cables to the inside of the channel without
the need to drill holes, reducing labor and speeding up installation. Compatible
with any cable tray system, channel systems can be more economical than conduit
in applications like communication, fire alarm, or call station and clock cabling.
WIRE BASKET
Produced from high-strength steel wires, a wire basket is a lightweight welded mesh
cable management system that provides superior flexibility and ease of installation.
This is usually best for maneuvering around obstacles. Low-voltage telecom cables,
control cables, and AV cables are traditionally installed in wire basket cable trays.
Codes and standards must be considered in advance. For instance, NEC 392.10
contains requirements on types of cable tray, cable size, cable types, and cable
spacing that must be used.
www.ieci.org | November/December 2021 | Insights Magazine 11