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Power Systems, Inc. 11
1.8 EMERGENCY CIRCUIT
ISOLATION METHOD
One effective way of preventing the generator from
being overloaded is to use the “Emergency Circuit
Isolation Method” (Figure 1.6).
Essential electrical loads are grouped together and
wired into a separate emergency distribution panel.
Load circuits fed by the emergency distribution panel
must be within the unit's rated wattage capacity. The
following apply to this type of isolation system:
• The transfer switch is installed between the main
and the emergency distribution panels as shown.
• The transfer switch must have an ampere rating
equal to the ampere rating of the emergency circuit.
Figure 1.6 – Emergency Circuit Isolation Method
* Ampere rating must equal or exceed the ampere
rating of the emergency distribution system.
** Ampere capacity is not to exceed the alternator
rating. Only these items will be powered by the
standby alternator. If the electrician sizes the load
properly, the alternator cannot be overloaded.
All wiring must conform to the National Electrical
Code, and all state and local codes. Consult a quali-
fied, licensed electrician.
The above illustration assumes the utility is supply-
ing 120/240-volt, single-phase electrical service.
1.9 TOTAL CIRCUIT
ISOLATION METHOD
If essential electrical loads cannot be grouped togeth-
er and wired into an emergency distribution panel,
you will have to select load circuits that the generator
will power during a utility power outage.
Be careful to avoid overloading the generator. The fol-
lowing apply to the “Total Circuit Isolation Method”
(Figure 1.7):
• The transfer switch is installed between the utility
service entrance and the distribution panel.
• The transfer switch ampere rating must be equal to
the main electrical service entrance rating.
Figure 1.7 – Total Circuit Isolation Method
* Ampere rating is equal to or larger than main (nor-
mal) power source.
** Use caution with this system to prevent overload of
the alternator during utility power failure. All load
items in the distribution panel must be individual-
ly turned off. Only certain items can be turned
back on during alternator operation. These items
should be specified by your electrician so as not to
overload the alternator.
All wiring must conform to the National Electrical
Code, and all state and local codes. Consult a quali-
fied, licensed electrician.
The above illustration assumes the utility is supply-
ing 120/240-volt, single-phase electrical service.
Service Disconnect
Section 1 — Installation
Guardian Air-cooled Generators