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How a Standby Generator Works

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Home standby systems consist of two components. The first component is the generator set which has an engine connected to a generator/alternator and control system. This generator burns fuel, which results in the production of electricity. The second component of the standby power system is the transfer switch.

Normal utility power runs through the transfer switch and then connects to the power distribution panel. It then runs to all of the electrical loads for a home. A backup power unit continually monitors the utility power voltage and when it falls to 85% of nominal, or fails completely, the automatic transfer switch senses there is a problem and signals the standby generator to start. A standby generator can take over and be running in less than ten seconds after power is interrupted. When the utility power comes back on, the transfer switch senses this and watches for an acceptable voltage to be reached. Once this voltage has been reached, the transfer switch reverses the process and your home goes back on utility power. The standby system then is considered to be off-line and will spend five minutes in a cool down mode and then automatically resets to a standby mode. All of this takes place automatically even if you are not at home.

Home standby generators run at a speed of either 1800 RPM or 3600 RPM. An 1800-RPM system will last longer and run more quietly. A 3600-RPM system has a smaller motor and is a lighter unit.
Standby generators come either air-cooled or liquid-cooled with the main difference being that air-cooled systems are louder and do not run quite as effectively. Liquid cooled systems are more expensive but are also more dependable. Typically, the 20kW and larger units are 1800-RPM and liquid-cooled.

The generator should be exercised monthly to be sure the system is ready for use. You can preset the time you want this procedure to take place so you do not have to be present. This process does not interrupt the utility power to your home. The standby power system can also be set to run manually by switching it to a “run” mode. The system should be tested on a regular basis to be sure it is in good running condition when needed.

You will need to change the oil and filters in a standby system. Generally, the oil should be changed after the first 50 hours of run time. After the initial oil change, you should change the oil about every 250 hours or every six months, whichever comes first.

Next Page: Selecting the Size of Standby Generator Needed

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