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4 Generac
®
Power Systems, Inc.
1.1 GENERATOR
This equipment is a liquid-cooled, engine-driven gen-
erator set. The generator is designed to supply elec-
trical power that operates critical electrical loads
during utility power failure. The unit has been facto-
ry-installed in a weather resistant, all metal enclosure
and is intended for outdoor installation only. Use this
generator as a source of electrical power for the oper-
ation of 120 and/or 240 volts, single phase loads.
These models are available. They are rated as follows:
Models 0047210 and 0047220: Provides 15,000
watts (15 kW) of single phase power.
Models 0047230 and 0047240: Provides 20,000
watts (20 kW) of single phase power.
Models 0047250, 0047251, 0047252, 0047253,
and 0047260: Provides 25,000 watts (25 kW) of sin-
gle phase power.
If this generator is used to power electrical
load circuits normally powered by a utility
power source, it is required by code to install
a transfer switch. The transfer switch must
effectively isolate the electric system from the
utility distribution system when the generator
is operating (NEC 701). Failure to isolate an
electrical system by such means results in
damage to the generator and may also result
in injury or even death to utility power work-
ers due to backfeed of electrical energy.
1.2 TRANSFER SWITCH
This generator system may include a matched auto-
matic transfer switch which is intended to be used in
conjunction with the Guardian generator. It is sup-
plied in either a NEMA 1 enclosure (15 kW model
004721, 20 kW models 004723) or a NEMA 3R
enclosure (25 kW models 004725). The NEMA 1
enclosure is intended for indoor use only. The NEMA
3R enclosure is weather proof and can be used
indoors or outdoors. Follow these rules:
• Install the transfer switch on a firm, sturdy sup-
porting structure.
• To prevent switch distortion, level the switch if nec-
essary. This can be done by placing washers
between the switch enclosure and the mounting
surface.
• Never install the switch where water or any corro-
sive substance might drip onto the enclosure.
• Protect the switch at all times against excessive
moisture, dust, dirt, lint, construction grit and cor-
rosive vapors.
• Failure to utilize a Generac/Guardian transfer
switch with this generator will void the warranty.
1.3 AUTOMATIC SYSTEM OPERATION
When this generator, along with its transfer switch, has
been installed and interconnected, a circuit board in
the generator panel constantly monitors utility power
source voltage. Should that voltage drop below a pre-
set value, and remain at such a low state for a preset
amount of time, the generator cranks and starts. After
the generator starts, the transfer switch transfers load
circuits so the generator can power them.
When utility source voltage has been restored, the
switch re-transfers back to the utility source voltage
and the generator then shuts down.
Please reference the transfer switch manual for spe-
cific information.
1.4 GENERATOR AC CONNECTION
SYSTEMS
The generator was shipped from the factory with its
stator AC output leads connected in a single-phase,
three-wire generator AC connection system (Figure
1.1). The stator assembly in this system consists of a
pair of stationary windings, with two leads brought
out of each winding. Each single winding can supply
120 volts AC, 60 Hertz. When the two windings are
connected in series, a 240 volts, 60 Hertz AC output
results. Typically the two “hot” leads in the circuit are
Wires No. 11 and 44. The “Neutral” leads are the
junction of Wires 22 and 33.
Figure 1.1 - Generator AC Connection System
1.5 MAIN CIRCUIT BREAKER
The generator’s main circuit breaker is included with
the unit as shipped from the factory. The breaker for
each unit is described in Figure 1.2 at the top of page
5.
1.6 GENERATOR FUEL SYSTEM
The generator has been factory tested and adjusted
using a natural gas fuel system. If propane (LP
requirements) gas is preferred, contact an authorized
service dealer. Refer to Secion 1.12.
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Section 1 - General Information
Guardian Liquid-cooled 15 kW, 20 kW and 25 kW Generators