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Figure 6-2.—Two speakers connected in series. |
CHAPTER 6
COMMUNICATIONS AND LIGHTING
Many advances in lighting and communications
have occurred in the past few years. With the cost of
energy rising daily and the demand for accurate and
reliable communications, any system that provides a
higher level of efficiency must be considered.
In this chapter we will discuss public address
systems, interoffice communications, and the
fundamentals of fiber-optic communication cables and
components. This chapter also will cover area
streetlighting, floodlighting, and security lighting.
PUBLIC ADDRESS SYSTEM
The type of public address system that you will
install, maintain, and troubleshoot is intended for
installation in administrative and living quarter areas.
This system will be used for general announcements,
for indoor talk-back paging, and to entertain or address
personnel.
A common system authorized by the General
Services Administration consists of one 100-watt solid-
state amplifier, four trumpet speakers with drivers, two
paging speakers, one dynamic microphone with floor
stand, and all accessory terminal fittings and hardware
required to operate this system. The set will conform to
the design and functional test requirements of
Underwriters Laboratory (UL) 813 Standard and the
wiring and design requirements of the National Fiie
Protection Association (NFPA) 70.
INSTALLATION
Before you install a public address system, refer to
the National Electrical Code© (NEC©) and the
manufacturers’ recommendations. Several factors must
be met for the permanent or temporary installation of a
public address (PA.) system.
We will discuss these factors for the installation of a
public address system, consisting of an amplifier
(console), speakers, and cable that are approved for this
system.
Amplifier
The solid-state amplifier comes with an ac power
cord that is terminated in a three-prong plug. The power
cord must be plugged into a three-wire, 120-volt, 60-
hertz grounded outlet. The cord will ground the
amplifier and the auxiliary power receptacle. The
auxiliary power receptacle is a three-wire grounded
outlet that supplies power to accessory sound
equipment. The receptacle will supply power only as
long as the amplifier is connected to a 120-volt power
source and turned on.
The amplifier will be internally wired with a circuit
breaker for protection. If the breaker trips, turn off the
amplifier and reset the circuit breaker. Turn on the
amplifier, and, if the breaker trips again, do not attempt
to reset it. A problem
investigate and correct.
Speakers
exists that you will need to
The speakers will be weatherproof and have
adjustable mounting brackets. The input impedance of
the speakers will match the amplifier output with a low-
frequency cutoff, as shown in figure 6-1.
Figure 6-1.—Total speaker impedance matches the output
impedance of the amplifier.
6-1
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