Commercial Stand-By Generators

Investing in a generator… a WISE decision

Cows need to be milked, milk needs to be cooled, livestock needs water, the silo unloader needs to get silage down for the cattle, feed conveyors need to work, hogs in confinement need ventilation, the family’s refrigerator and freezer needs to keep food cold.

If you have a critical need for uninterrupted power, you may want to consider purchasing a stand-by generator to protect against such interruptions.

Investing in a standby generator is like paying a premium for insurance. You hope you never have to use it, but if you do need it, it is well worth the price. A standby generator reduces the risk of losses due to power outages.

Runestone Electric allows a lower rate for single and three phase accounts to have a back-up generator. A double throw transfer switch is required. Power-Take-Off (PTO) units on tractors do not qualify. The generator must be a permantly mounted system with automatic operation.

A double throw transfer switch needs to be installed at the main service entrance just after the meter so the generator is always isolated from incoming power lines. This switch keeps generated power from feeding back over Runestone Electric´s supply lines, eliminates generator damage when the power is restored, and protects power line repair crews.

For more information about standby generators and how one could help protect your farm operation in time of need, contact the Runestone Electric Member Services.

Selecting The Generator

When selecting your standby generator, four basic considerations should be made:

    1. The size (KW) of the unit that will be required to handle the job. You must determine what your total load will be. Your generator must NOT be overloaded or damage to the unit will occur.
    2. The proper speed required for your generator. Typically 1800 RPM slow speed revolving armature units are selected for more continuous duty applications. High speed, 3600 RPM, revolving field units are less expensive but are not intended for continuous use.
    3. The starting method for your generator must be an electric start and automatic.
    4. The fuel required. Gasoline, diesel or propane?
Sizing Your Generator

Generators need to be sized correctly to prevent overloading. Overloading a generator can cause poor power quality, and may damage the generator and electrical appliances in your home and out-buildings. In order to determine the generator’s size, make a list of what will be operating, and add the wattage of all the equipment. Be particularly cautious when calculating and connecting motor loads as starting wattage can be considerably higher than operating wattage. Refer to motor nameplates when making these calculations. Otherwise, horsepower can be used to determine the generator size. Motors require three to five times more current for starting than for continuous running.



Equipment Watts
Milking machine 800-5,000
Bulk milk cooler 1,500-12,000
Water pump 500-2,500
Water heater 4,500
Space heater 1,000-5,000
Ventilation fans 300-1,000
Silo unloader 2,000-7,500
Electric fencer 7-10
Feed grinding 1,000-7,000
Feed mixing 800-2,000
Feed conveyor 800-5,000
Security lights 100-500
Shop tools 300-1,500

Typically, when sizing a generator, it is wise to add the starting wattage of the largest motor to the running wattage of all other necessary motors and equipment. Identify the loads that can be interrupted for extended periods, and note those that are critical like milking equipment, water pumping, refrigerations, etc.

Installing the Generator

If you are considering buying a standby generator for your home, farm or business, make sure it’s properly installed by an experienced electrician and follow these guidelines:

Always have a qualified electrician install the generator. To be properly installed, a generator must be connected to your home’s wiring through a double-throw, double-pole transfer switch as required by the National Electric Code. This will ensure that the house wires are isolated from the utility wires, meaning the generator and the electric utility’s power cannot be energized at the same time. When you run a generator without a double throw switch, you may fee 240 volt current back into the transformer. The transformer will “step it up” to 7,200 volts that could give a lethal shock to a lineworker who considered the line dead.

Never connect a portable electric generator or a motorhome/RV generator directly to your home’s electrical system during a power outage. Electricity could backfeed into the power lines and endanger Runestone Electric workers and damage your equipment.