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Standby Electric Generators

 Ken Hellevang, Extension Engineer

Standby Electric Generators

An emergency source of power is important during a flood or other disaster for farms with critical equipment, such as bulk milk-handling and mechanical feeding equipment, mechanically ventilated production facilities, and brooders or other facilities requiring constant heat.

An alternative power source also is vital for homes to keep sump pumps running and the heating system working, particularly in areas that may experience power interruption.

A standby electric generator could prevent costly losses during a power failure.

Types of Generators

Standby generators are engine- or tractor-driven. They can be stationary or portable. Engine-driven models are equipped with a manual or automatic starter and, depending on the model, will run on gasoline, LP (bottled) gas or diesel fuel.

Safety Guidelines

Here are some basic safety rules to follow when using a standby generator:

  • Do not operate the generator in an enclosed or partially enclosed space. Gasoline or diesel engines may produce deadly levels of carbon monoxide. Carbon monoxide can accumulate in a building even with a large door, such as an open garage door. Wind blowing into an attached garage can push the carbon monoxide into the house.
  • If you operate a generator in an enclosed building, you must use engine exhaust ducting to vent the engine exhaust outdoors and away from the building.
  • Choose a generator that provides the power at the same voltage and frequency as your power lines supply. Most power lines supply 120/240-volt, single-phase, 60-cycle alternating current to homes and farms.

Selecting the Right Generator

To help you buy the proper sized generator, you need to decide what you must keep running, such as a sump pump and furnace or certain farm equipment (milk cooler or ventilation fan, for instance). A full-load system will handle an entire farmstead’s electrical needs. A smaller and less expensive part-load system may be enough to handle essential equipment during an emergency.

Power takeoff generators are adequate for most farms, provided the generators are the right size to start the largest motor. Also, power takeoff generators can be mounted on trailers and are about half the cost of engine-driven units.

An air-cooled engine often is used for generators up to 15 kilowatts. A liquid-cooled engine is necessary for generators larger than 15 kilowatts. Generators must have an engine capacity of 2 to 2 1/4 horsepower with the proper drive system for each 1,000 watts generated.

Motors typically require four times the power to start as they do to run. Estimate power requirements from equipment nameplates when possible.

As a guide, electric motors require approximately 4,000 watts of power to start and 1,000 watts of power to run for every horsepower of output. A typical home operating a water pump, refrigerator, freezer, furnace blower (gas furnace) and a few lights will require about 5,000 watts of peak usage for starting and 2,000 watts for continuous operation.

Installation

Electrical equipment normally is plugged into a smaller generator. Extension cords must be the proper size based on the electrical load and distance from the generator. The proper voltage may not be provided to a motor at the end of a very long extension cord, which will result in damage to the motor.

Do not connect the generator to a home or farm electrical system without a transfer switch that disconnects the farm or home from the power line and connects to the generator. The wiring system must be isolated from the power lines using a double-throw transfer switch to prevent the generator from feeding electricity back into the power line. This protects linemen who may be working to restore your electrical service. Also, without a double-throw switch, the generator can be ruined due to overloading.

Operation

The automatic-start generator should start automatically when the power fails and stop when your power is restored. If you are using an engine-driven generator with a manual start or a tractor-driven unit, here are some basic steps to follow:

  • Alert your electric utility that you’ve lost power.
  • Turn off or disconnect all electrical equipment.
  • Start the generator and bring it up to proper speed (1,800 or 3,600 revolutions per minute).  The voltmeter will indicate when the generator is ready to carry the load.
  • Make sure the transfer switch is in the generator position.
  • Check on your arrangements to get rid of exhaust fumes.
  • Start the largest electrical motor first, adding other loads when each additional motor is up to operating speed. Do not add too much too fast.
  • If the generator stops, repeat all but the first step.
  • Check the voltmeter frequently. If the voltage falls below 200 for 240-volt service or 100 for 120-volt service, reduce the load on the generator by turning off some electrical equipment.
  • When commercial power is restored, put the transfer switch in the normal power position and stop the standby generator.

Maintenance

Make sure your standby generator is clean and in working order at all times so it will be ready when you need it. Dust and dirt accumulations on the motor can cause it to overheat when it is running.

Follow the generator manufacturer’s maintenance instructions. Running the generator briefly at regular intervals will keep it in good working order.

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