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• NFPA No. 30, FLAMMABLE AND COMBUSTIBLE LIQUIDS
CODE.
• NFPA No. 10, INSTALLATION, MAINTENANCE AND USE OF
PORTABLE FIRE EXTINGUISHERS.
OTHER PUBLISHED STANDARDS
In addition to NFPA standards, the following information pertaining
to the installation and use of standby electric systems is avail-
able:
• Article X, NATIONAL BUILDING CODE, available from the
American Insurance Association, 85 John Street, New York,
N.Y. 10038.
• AGRICULTURAL WIRING HANDBOOK, obtainable from the Food
and Energy Council, 909 University Avenue, Columbia, MO,
65201.
• ASAE EP-364.2, INSTALLATION AND MAINTENANCE OF FARM
STANDBY ELECTRIC POWER, available from the American
Society of Agricultural Engineers, 2950 Niles Road, St. Joseph,
MI 49085.
• A52.1, AMERICAN NATIONAL STANDARD FOR CHIMNEYS,
FIREPLACES AND VENTING SYSTEMS, available from the
American National Standard Institute, 1430 Broadway, New
York, N.Y. 10018.
BASIC STANDBY ELECTRIC SYSTEM
Figure 2.1 shows a schematic diagram of a basic standby electric
system. Both the UTILITY power supply and the STANDBY (GEN-
ERATOR) output are connected to an approved transfer switch.
The transfer switch is required by electrical code and serves the
following functions:
• Permits the LOAD circuits to be connected to only one power
supply at a time.
• Prevents electrical backfeed between the generator and the
UTILITY power circuits.
Notice that both the STANDBY and the UTILITY power supplies to
the transfer switch are protected against overload by a main line
circuit breaker.
Figure 2.1 – Basic Standby Electric System
EMERGENCY CIRCUIT ISOLATION
METHOD
This prevents overloading the generator by keeping electrical
loads below the wattage/amperage capacity of the generator. If
the generator is powering only critical loads, within the wattage/
amperage capacity, during utility power outages, consider using
the emergency circuit isolation method.
Critical electrical loads are grouped together and wired into a sepa-
rate "Emergency Distribution Panel." Load circuits powered by that
panel are within the wattage/amperage capacity of the generator
set. When this method is used, it is difficult to overload the genera-
tor. The transfer switch must meet the following requirements:
• It must have an ampere rating equal to the total amperage rating
of the emergency distribution panel circuit.
• Have it installed between the building's main distribution panel
and the emergency distribution panel.
TOTAL CIRCUIT ISOLATION
METHOD
When a generator capable of powering all electrical loads in the
circuit is to be installed, use the "Total Circuit Isolation Method." It
is possible for the generator to be overloaded when this isolation
method is employed. The following apply to the transfer switch in
this type of system.
• Ampere rating of the transfer switch must equal the ampere
rating of the normal incoming utility service.
• The transfer switch is installed between the utility service
entrance and the building distribution panel.
GROUNDING THE GENERATOR
The National Electrical Code requires the frame and external electri-
cally conductive parts of this equipment to be properly connected
to an approved earth ground and/or grounding rods. For that
purpose, a GROUND LUG (Figure 2.2) is provided on the genera-
tor mounting base. Consult a qualified electrician for grounding
requirements in the area. Grounding procedures must meet local
regulations.
Figure 2.2 – Generator Grounding Lug (typical)
Installation
9
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