How does a Home Standby System Work?

A Cummins Onan residential standby system (RSS) will provide power to your home when the utility company’s supply fails. There are many causes for power outages – storms, accidents, or shortages – at times when you least want your home to be without electricity. By having a standby system, you will have a seamless and automatic transfer of power to your generator that will enable you to go on with your life and keep your family comfortable and secure.

There are two components of a home standby system:

  1. Residential Standby (RS) Unit  – a Cummins Onan generator set that produces the power needed to run your essential home systems in the event of an outage.
  2. Automatic Transfer Switch (ATP) – a Cummins Onan RSS Automatic Transfer Switch senses when the power supply from the utility company has been interrupted and immediately initiates the transfer of responsibility to the generator.

Automatic and Seamless Transfer Process

1. Voltage coming into your home from the utility is monitored by the Cummins Onan Automatic Transfer Panel (ATP).
2. When the ATP senses that the power to your home drops below an acceptable level it will send a signal to start the Cummins Onan Residential Standby (RS) unit.
3. The ATP will then automatically disconnect the utility power from your home’s electrical circuits and reconnect them to the RS unit.
4. The RS unit will continue to supply power to your home until the electricity is restored by the utility company.
5. The ATP will sense when the utility power is restored and automatically disconnect your RS generator set from your home’s electrical circuits and reconnect the power from the utility.
6. Lastly, the RS system will automatically reset itself to be ready for the next power outage.

Modes of Operation

Normal Utility Power Mode

  1. Power is being supplied by the utility.
  2. Generator is in standby mode.
  3. Transfer panel monitors electrical loads in the home and voltage levels coming from the utility.

Power Outage Occurs

  1. Voltage supplied by utility falls below 85% of nominal, transfer panel will initiate the residential standby system.
  2. Within 10 seconds of power failure, the generator set is connected to the home and power is restored.

Utility Power Returns

  1. Once the standby system is in effect, the transfer panel will continue to monitor the power supplied by both the generator set and the utility.
  2. If power is restored and the transfer panel determines the supply’s voltage is at an acceptable level, it will transfer the electrical load back to the utility.
  3. The transfer panel will signal the generator to go “off-line” and it will operate automatically for five minutes through a cool down cycle.
  4. Following cool down the generator will reset to standby mode.

Automatic Exercise Cycle

  1. Each month, a time of day can be set for the residential standby system to run automatically. This exercise cycle is recommended to maintain system readiness.
  2. During the exercise period, power produced by the generator will not be connected to the home’s circuit – utility supply will be maintained.

System Testing

    • A power failure can be simulated by opening the main circuit breaker ahead of the transfer panel. This will test the entire residential standby system.
    • Re-closing the utility breaker will restore power and the standby system will go through the retransfer sequence and return itself to standby mode.