4 Generac®Power Systems, Inc.
GENERATOR
This equipment is a liquid-cooled, engine-driven gener-
ator set. The generator is designed to supply electrical
power that operates critical electrical loads during util-
ity power failure. The unit has been factory-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 operation of 120
and/or 240 volts, single phase loads.
These models are available. They are rated as follows:

Model 004188: Provides 15,000 watts (15 kW) of 1 phase power.

Model 004189: Provides 15,000 watts (15 kW) of 1 phase power.

Model 004370: Provides 20,000 watts (20 kW) of 1-phase power.

Model 004371: Provides 20,000 watts (20 kW) of 1-phase power.

Model 004474: Provides 25,000 watts (25 kW) of 1 phase power.

Model 004475: Provides 25,000 watts (25 kW) of 1 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 iso-
late the electric system from the utility distribu-
tion 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 workers due to backfeed of electrical ener-
gy.
TRANSFER SWITCH
This Guardian system includes a matched automatic
transfer switch which is intended to be used in con-
junction with a Guardian generator. It is supplied in
either a NEMA 1 enclosure (15 kW models 004188, and
004189, and 20 kW models 004370, and 004371) or a
NEMA 3R enclosure (25 kW models 004474 and
004475). 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 support-
ing structure.
• To prevent switch distortion, level the switch if neces-
sary. This can be done by placing washers between
the switch enclosure and the mounting surface.
• Never install the switch where water or any corrosive
substance might drip onto the enclosure.
• Protect the switch at all times against excessive mois-
ture, dust, dirt, lint, construction grit and corrosive
vapors.
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 preset
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.
GENERATOR AC CONNECTION SYSTEMS
The generator was shipped from the factory with its sta-
tor AC output leads connected in a single-phase, 3-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

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.
GENERATOR FUEL SYSTEM
This unit has been factory tested and adjusted using a
natural gas fuel system. If propane (LP) gas is preferred,
contact an authorized service dealer.
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Section 1 - General Information
Guardian Liquid-cooled 15 kW, 20 kW and 25 kW Generators