Building Design and Construction Handbook - Merritt - Ventech!

15.74 SECTION FIFTEEN
type uses thousands of small air terminals spread along the high points of a structure
to constantly dissipate any electrical charge in the air before it can build up high
enough to induce a lightning stroke.
The electrical wiring in a building is especially susceptible to the effects of a
lightning stroke. To minimize these effects, a multilevel protective approach is used.
Lightning arresters, which are connected from the phase wires to ground, are provided
on the utility company lines and at the various voltage levels down to utilization
voltage. Usually of the metallic oxide varistor (MOV) type, the arresters
present a very high resistance to ground at normal system voltage, but quickly
collapse to zero resistance during a lightning discharge, dissipating the discharge
to ground.
At sensitive electronic loads, it is necessary to provide a higher level of protection
against the effects of lightning and other voltage disturbances by providing
transient-voltage surge suppressors (TVSS). These devices utilize silicon-controlled
rectifiers (SCR) or combinations of SCRs and MOVs that closely limit the peak
surge voltage and react within 5 nanoseconds to voltage surges.
15.19.2 Fire-Alarm Systems
These provide means of detecting a fire, initiating an alarm condition, either manually
or via automatic detection, and responding to that alarm condition. A firealarm
system consists of a central fire-alarm control panel; perhaps several remote
subpanels; initiating devices, such as manual pull stations, smoke detectors, sprinkler-flow
switches; and alarm devices, such as horns, gongs, and flashing lights.
The control panel provides power to the system components and monitors the status
of all of the initiating devices. It also monitors all fire-protection-system functions
and supervises the condition of the wiring. In addition, the control panel provides
outputs, under alarm conditions, to shut down air-conditioning fans, initiate smoke
evacuation, close smoke doors, initiate elevator capture, release fire suppressants,
activate alarm devices, and notify the fire department.
Larger systems are generally of the addressable type. The control panels are
microprocessor based. Each device has a digital electronic identifier, or address. A
control panel sequentially polls each device to check its status. This method allows
as many as 30 devices to be connected to a single circuit and can greatly reduce
the wiring costs of the fire-alarm system.
Design of the fire-alarm system must comply with the requirements of the National
Fire Protection Association and local governing authorities. It is essential that
fire-alarm systems be designed to interface with the HVAC system controls for unit
smoke detection and shutdown and for smoke-exhaust-system control. Fire-alarm
systems also should interface with the fire-protection system to monitor building
sprinkler-system components and other fire-suppression systems. System design
should also consider the building type and occupancy in selecting components and
materials. Particular care should be taken in design of fire-alarm systems for highrise
buildings (over 75 ft high), which will require a firefighter’s control panel, fire
phone system, and voice-evacuation system as a minimum.
15.19.3 Communications Systems
These may include telephone, paging, and intercom systems. Telephone systems in
large buildings generally have telephone service to a computerized business