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BASIC STATIONARY EMERGENCY
GENERATOR ELECTRIC SYSTEM
Figure 9.1 shows a schematic diagram of a basic standby elec-
tric system. Both the UTILITY power supply and the Stationary
Emergency Generator output are connected to an approved trans-
fer switch. The transfer switch is required by electrical code and
serves the following functions:
•
Allows 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.
Figure 9.1 – Basic Stationary Emergency Generator
Electric System
Notice that both the Stationary Emergency Generator and the
UTILITY power supplies to the transfer switch are protected against
overload by a main line circuit breaker.
STATIONARY EMERGENCY
GENERATOR 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 designated loads, within the wattage/
amperage capacity, during utility power outages, consider using
the emergency circuit isolation method.
Designated electrical loads are grouped together and wired into a
separate "Standby Distribution Panel." Load circuits powered by
that panel are within the wattage/amperage capacity of the genera-
tor set. When this method is used, it is difficult to overload the gen-
erator. The transfer switch must meet the following requirements:
•
It must have an ampere rating equal to the total amperage rating
of the standby distribution panel circuit.
•
Have it installed between the building's main distribution panel
and the standby distribution panel.
Operation
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.
CONNECTION DIAGRAMS
All wiring in the Stationary Emergency Generator electric power
system must be in strict compliance with applicable codes, stan-
dards and regulations. Such wiring must be properly supported,
routed, and connected. In addition, wiring must be properly sized
to carry the maximum load current to which it will be subjected.
The connections between the generator and transfer switch will
vary depending on the equipment ordered. In each case there are
two types of interconnections, load wiring and control wiring.
Control wiring must always be run in a separate conduit from
the load wiring.
Make sure to turn OFF both the NORMAL
(UTILITY) and GENERATOR (EMERGENCY)
power supplies before trying to connect
power source and load lines to the transfer
switch. Supply voltages are extremely high
and dangerous. Contact with such high volt-
age power supply lines causes extremely
hazardous, possibly lethal, electrical shock.
Be sure to maintain proper electrical clear-
ances between live electrical parts and
grounded metal. Allow at least one-half inch
of clearance for circuits up to 400 amps.
NOTE:
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