Standby Power Gets Smart: New controllers help home generators work more effectively

Shutterstock / Tukang Desain
Shutterstock / Tukang Desain
Published On
Jan 14, 2022

If you had to pick which electrical branch circuits or feeders to supply power to during a utility company power outage, what would you choose, and would that make you popular or not in your household? If you are the electrical contractor or electrician installing a generator or other supplementary power source to a home, would you know what circuits to supply and what not to supply?

Does the customer know that a generator must be periodically exercised or turned on for a period to ensure everything is working properly? Can the homeowner remember to exercise the equipment, or should you sell them a service contract that will ensure proper maintenance so the power source will function appropriately when needed?

Making choices

These may sound like strange questions. However, many of us have had to make those decisions and then justify them, or have a customer unhappy that the system does not operate properly when needed. A good electrician must ask the customer major questions prior to bidding on the installation project. The customer may not be required to make choices where the temporary power source is large enough to supply whole-house power. But not everyone has enough money to provide larger generators, and smaller power sources, such as small generators, require certain choices to be made.

Many ECs and their customers are not familiar with “state-of-the-art” digital controllers that handle a larger variety of functions for monitoring and controlling standby generators. These controllers turn the system on and off, monitor safety sensors and notify the homeowner when service is required. These smart controllers are easy to use and permit the monitoring of operating parameters, status checking and generator run logs. The controller can do an automatic startup once a week, every other week or once a month, with automatic customer notification to provide the homeowner with peace of mind.

The controller monitors the utility company power, and if the utility company’s voltage drops by 60% or more, the controller identifies the voltage drop as a power outage and initiates a generator start sequence that begins with a “nuisance” delay, as described by one manufacturer. The nuisance delay is a period of time lasting 10–30 seconds, during which the generator does not start in case the power outage and voltage drop was only momentary.

When the generator does start, the controller monitors and regulates the generator’s output voltage to keep it within 1% of the operating level. This regulation even occurs when a large motor, such as an air conditioner, starts causing a momentary sag in voltage due to high current in the motor’s startup current.

The controller can also monitor the frequency and adjust the generator’s engine speed to maintain a constant 60 hertz (60 cycles per second) frequency. Once utility company power has been restored, the home is switched back to that power source. There is a time delay where the utility company power is monitored to ensure it is not intermittent, after which the switchover is completed, with the controller keeping the generator running for at least one minute without load to permit it to cool down before turning it off.

The controller monitors the generator’s battery, regulates the current to the battery to prevent overcharging and can be programmed to alert the homeowner if the battery is about to fail or has failed. The controller will also automatically shift the generator down if there is insufficient oil pressure, high engine speed or temperature, improper wiring, internal or external faults, over-cranking or low frequency. The controller keeps a log of all events, which is accessible by the homeowner or the electrical contractor servicing the unit.

These digital controllers can be programmed to pick up certain important loads and shed others as necessary to ensure that whatever loads are important to the homeowner can operate when needed. Section 702.4(B) of the National Electrical Code provides requirements for optional standby system capacity. Where manual transfer equipment is used (the utility company power is lost), the optional standby system must have adequate capacity and rating for the supply of all equipment intended to be operated at one time. The homeowner is permitted to select the loads connected to the system. Where automatic transfer equipment is used, the standby source must be capable of supplying the full load transferred by the automatic transfer equipment. An additional option permits a load management system that automatically manages the connected load to a capacity sufficient for the generator’s maximum capacity.

We have come a long way over the past decade or so in providing safety and reliability for our standby systems, while still providing power during utility company outages.

About the Author

Mark C. Ode

Fire/Life Safety, Residential and Code Contributor

Mark C. Ode is a lead engineering associate for Energy & Power Technologies at Underwriters Laboratories Inc. and can be reached at 919.949.2576 and Mark.C.Ode@ul.com.

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