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How A Home Standby System Works
 An Onan Home Standby System has two components:
- An Onan generator set to produce the power needed to run your essential home systems.
- An automatic transfer panel that immediately senses when utility power has been interrupted, transferring responsibility to the generator.
Below is a basic description of how these components operate to provide
you with the comfort and convenience your family depends on. Please
note that this is an overview only. For specific questions about
operation and maintenance, please refer to the operator's manual or
contact an Onan dealer or distributor.
Normal Utility Power Mode:
Under normal circumstances when utility power is available, utility
power runs through the transfer panel contactors, and connects the
power to the distribution panel and then to all the electrical loads in
a home. The existing electrical system is not compromised in any way by
integrating an automatic standby power system in a home. A battery
charger installed in the transfer panel enclosure is powered by the
utility to keep the starting battery in the generator set charged.
Power Outage Occurs:
When utility power voltage falls to less than 85% of nominal, or fails
entirely, the standby power system will automatically go through a
start sequence and connect to a home. The transfer panel control
constantly monitors the power quality from both the utility source and
the generator set. When the transfer panel control senses unacceptable
utility power, the control waits for 3 seconds and then sends a signal
to start the generator set engine. If the utility power returns before
3 seconds has passed, the generator set engine will not be signaled to
start. When the start signal is received, the engine starts and reaches
the proper operating speed and AC power is available at the generator
set. The transfer panel control senses this, waits for 3 seconds and
will then transfer generator set power to the home through the transfer
panel contactors. This sequence of operations will usually occur in
less than 10 seconds from the time the power outage occurred to the
time when generator set power is connected.
Utility Power Returns:
When utility power comes back on and returns to your home, the transfer
panel control senses this and will watch for acceptable voltage. After
checking for acceptable utility voltage for five minutes, the transfer
panel control will signal the transfer panel contactors to re-transfer
the load back to the utility source and disconnect the generator set
source. At this point, the generator set is "off-line" and will be
operated automatically another five minutes to properly cool down.
After the cool down cycle, the generator set will be turned
automatically off and reset to standby mode.
Automatic Exercise Cycle:
The generator set should be exercised monthly for system readiness. The
time of day can be set for the system to operate and it will
automatically start and run for a preset period of time. During this
exercise period, the power available from the generator set WILL NOT be
connected to the home, and utility power will not be interrupted.
Manual Exercise Operation:
The generator set can be operated at anytime from the generator set
control panel behind the service access door. Simply move the
"RUN/OFF/AUTO" switch to "RUN", and the generator set will start and
run. Power available from the generator set WILL NOT be connected to
the home, and utility power will not be interrupted. The switch must be
returned to the "AUTO" position for fully automatic operation.
System Testing:
The entire system can be tested manually by simulating a power failure.
This can be done by manually opening the main circuit breaker ahead of
the transfer panel. The standby power system will then go through the
start sequence and pickup the home electrical loads. Manually
re-closing the main utility breaker will then signal the standby power
system to go through the retransfer sequence and return to standby
mode.
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