Handbook for Sound Engineers

440 Chapter 14

ing characteristics. It can also be substituted for all
applications below.
Riser—Suitable for use in a vertical run, in a shaft, or
from floor to floor, and has fire-resistant characteristics
capable of preventing the spread of fire from floor to
floor. It can also be substituted for all applications
below.
General Purpose—Suitable for general-purpose use,
with the exception of risers, ducts, plenums, and other
space used for environmental air, and is resistant to the
spread of fire. It can be substituted for the applications
below.
Restricted Applications—Limited use and suitable for
use in dwellings and in raceways and is flame retardant.
Restricted use is limited to nonconcealed spaces of 10 ft
or less, fully enclosed in conduit or raceway, or cable
with diameters less than 0.25 inches for a residential
dwelling.

14.28.2 Cable Types

Signal cable used for audio, telephone, video, control
applications, and computer networks of less than 50 V is
considered low-voltage cabling and is grouped into five
basic categories by the NEC, Table 14-35.

All computer network and telecommunications
cabling falls into the CM class. The A/V industry
primarily uses CM and CL2 cabling.
Table 14-36 defines the cable markings for various
applications. Note plenum rated cable is the highest
level because it has the lowest fire load which means it
does not readily support fire.

14.28.3 NEC Substitution Chart

NEC cable hierarchy, Fig. 14-23 defines which cables
can replace other cables. The chart starts with the high-
est listed cable on the top and descends to the lowest
listed cable on the bottom. Following the arrows defines

which cable can be substituted for others. Fig. 14-24

defines the Canadian Electrical Code (CEC) substitu-

tion chart.

14.28.4 Final Considerations

The National Electrical Code is widely accepted as the

suggested regulations governing the proper installation

of wire and cable in the United States. The code is

revised every three years to keep safety in the forefront

in wire and cable manufacturing and installation. Even

though the code is generally accepted, each state, county,

city, and municipality has the option to adopt all of the

code, part of the code, or develop one of its own. The

local inspectors have final authority of the installation.

Therefore, the NEC is a good reference when questions

arise about the proper techniques for a particular instal-

lation, but local authorities should be contacted for veri-

fication.

When choosing cable for an installation, follow these

three guidelines to keep problems to a minimum:

1. The application and environment determine which
   type of cable to use and what rating it should have.
   Make sure the cable meets the proper ratings for
   the application.


2. If substituting a cable with another, the cable must
   be one that is rated the same or higher than what
   the code calls for. Check with the local inspector as
   to what is allowed in the local area.


3. The NEC code is a general guideline that can be
   adopted in whole or in part. Local state, county,
   city, or municipal approved code is what must be
   followed. Contact local authorities for verification
   of the code in the area.

The local inspector or fire marshal has the final

authority to approve or disapprove any installation of

cable based on the National Electric Code or on the

local code.

Table 14-35. The Five Basic NEC Cable Groups

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

Table 14-36. Cable Applications Designations

Hierarchy

Cable Family

Application MP CM CL2 CL3 FPL PLTC

Plenum MPP CMP CL2P CL3P FPLP –

Riser MPR CPR CL2R CL3R FPLR –

General

Purpose

MP, MPG C M ,

CMG

CL2 CL3 FPL PLTC

Dwelling – CMX CL2X CL3X – –