User manual

6 ExtroNews 12.1 January/February 2001
The building authorities (usually county
or city) in your locality adopt standards and
codes to which construction must conform
for the overall good and safety of the
community. Remember that regardless of
national codes and standards, the local
building authorities have the last word on
what is considered acceptable building
and wiring practice in your area.
For both high voltage and low voltage
electrical wiring, all building authorities
adopt standards from the National
Electrical Code, or NEC. The NEC is a
collection of requirements for electrical
wiring and appliances that safeguard
against electrical fire and electrocution. A
committee under the supervision of the
National Fire Protection Association, NFPA,
creates the NEC. The NEC is but one code
document among many created by the
NFPA. Go to www.nfpa.org for more
information. I think it’s important to bring
up the difference between a standard and
a code. A standard is a level of
performance that may be adopted as an
option, but a code is a mandate imposed
by some authority.
“I’ll take CABLES for 50, please.”
All signal cable used for computer
networks, telephone, video, audio, and
Deciphering Cable Safety Ratings and
Applications
TECHNICALLY SPEAKING...
by Steve Somers, Vice President of Engineering
H
ave you ever found yourself confused or unsure of the type of wire
or cable to use in a project as it relates to local codes and safety
requirements? What do the various cable safety ratings mean? What
materials and characteristics make one cable less flammable than
another? What is meant by halogen-free cable? Is plenum cable cheaper
to run than cable in conduit? I’m going to try to answer these and
hopefully many other questions about cable fire safety and application.
control applications of less than 50 volts is
considered low voltage cabling. Low
voltage cabling is categorized into the
following five basic groups within the
National Electrical Code (NEC):
Cable Type: Use:
CM
Communications
CL2, CL3 Class 2, Class 3
remote-control, signaling,
and power-limited cables
FPL Power-limited fire
protective signaling cables
MP Multipurpose cable
PLTC Power-limited tray cable
Fire safety ratings under the NEC are
conducted according to a common group
of flame retardancy tests, which makes the
cable markings similar across all of these
designations. The NEC’s cable substitution
hierarchy for fire safety is shown in
Table 1. Video, audio, and low voltage
control cables fall into Class 2 typically due
to the available power limits set in
the NEC. All computer network and
telecommunications cabling falls into the
CM class. CM and CL2 categories of cabling
are of primary concern in the A/V industry.