Emergency Power Information

An emergency source of power is a wise investment for every farm and household due to constant and consistent heat or refrigeration needs. A standby power generator will help prevent costly losses during temporary local power failures.

Generators can be either engine or tractor driven.

The advantages of engine-driven generators include more efficient fuel use, longer periods of continuous operation, lower noise levels, and quicker start-up after power outages. The main disadvantage of engine-driven generators is the high initial cost.

Tractor driven generators are powered from the tractor’s PTO shaft. The advantages of these generators include lower initial costs and less maintenance because an engine is eliminated. The disadvantages of tractor driven generators include noisier operation and limited output capacity. These generators also take several minutes to start up and may be trailer mounted for portability.

Peak Load and Operating Load

The generator “peak rate” is the power produced by the generator for short term overloads such as when a motor starts. Operating load is the power produced on a continuing basis after initial startup and is much lower than peak.

Type and Amount of Power Needed

Your emergency power will need to be the same type, same voltage and same frequency as supplied by the power lines. Generally this will be 120/240 volt, single-phase, 60-cycle alternating current. Alternating current may also be referred to as AC. This type of electrical system can power single-phase motors from 1/4 to 10 horsepower; bigger will require special or three phase power.

Electric motors for agricultural use require about four times more power to start than to run. The start-up power peak load can be estimated by multiplying the operating load by 4. Heaters and lights are resistance loads, so the start-up and operating loads are the same.

A full electrical load system provides the total required electrical load for the entire farmstead. Automatic-start, engine-driven generators are recommended for full load systems to prevent power disruptions. The main advantage of full load systems is that all equipment can be started at the same time. Furthermore, the greater generator capacity of full load systems allows more flexibility to add equipment.

Partial Electrical Load Systems are recommended and used when only critical electrical loads need to be met. The generator capacity for a part load system is much smaller and more economical than that for a full load system. Tractor driven generators and Welder Generator Combinations are good choices for emergency power when only partial power is needed for critical projects. The main advantage of part load systems is that lower capacity generators are less expensive and are designated to meet specific needs.

Sizing the Generator for the Job Requirements

Whether opting for a Full Load or Partial Load Generator System properly sizing the unit for the job will keep you out of trouble.

Assume the start-up load is four times the operating load. Size the generator using the following steps:

For Full Load System:
1.  List the operating and start-up loads of all motors to be connected to the generator. Note that the start-up load is the same as operating load for heaters and lights as previously mentioned.

2.  Total the start-up load.

3.  Add 20% to the total for future expansion, then round up to the nearest 5 kW.

For a Partial Load System

1. List the operating and start-up loads of only the critical motors in order of highest start-up load first. Resistance loads such as heater and lights should be added last.

2.  Determine the peak load as each of the loads is added. Then add the start-up load of the next piece of equipment to the operating load of the running equipment.

3.  When the desired peak Load is established add 20% to the total for future expansion, then round up to the nearest 5 kW.

Tractor Driven Power Unit

If you plan on using a Tractor-Driven Generator the tractor should have at least twice the horsepower as electrical output of the generator. For example, to determine the tractor size for a 50 kW generator you multiply 50 times 2 to determine that a 100 HP tractor is needed.

Connecting to the System

When connecting the Generator System so that the existing wiring will feed the power it must be connected to the wiring system through a transfer device that prevents power from feeding back in the supply line.  Install a double-pole transfer switch to prevent feedback. Contact your local power supplier before installing a generator and have a licensed electrician make all electrical connections. Wiring should be installed in accordance to local codes and the requirements of the local power supplier.

Fixed type generators should be anchored to a 6-inch concrete pad and sheltered from the weather. When housed inside provide half of a square foot of inlet and outlet air opening for each 1 kW of generator rating to allow excess heat to escape. Combustion fumes must be carried outdoors safely and away from building inlets. Exhaust pipes should be at least 6 inches from combustible material.

Automatic start generators should start automatically when power fails and stop when power is restored.

When using manual start engine driven or tractor driven generators follow this procedure:

  • Call power supplier and advise them of power outage
  • Turn off or disconnect all electrical equipment before starting
  • Position the tractor or engine for belt of PTO drive
  • Start the unit and bring the generator up to proper speed (540 or 1000 rpms)
  • Check voltage to indicate when the generator is ready to carry the load
  • Put the transfer switch in the generator position
  • Turn on the motors one at a time, starting with the largest motor first
  • Monitor voltage and keep 240 V (±10%) at generator
  • Put the transfer switch in normal power position when commercial power is restored
  • Stop the standby unit

The length of time a generator can run depends on the size of the fuel tank and the size of the load on the generator. Higher loads require more fuel. Gasoline and diesel fueled models use slightly less fuel than those fueled by LP gas. You can also check with the manufacturer for specific information.


Proper Maintenance is an absolute must so your generator should be kept clean and in good running condition so it will always be ready for immediate use. Dust and dirt accumulations on the motor can cause it to overheat when running. To keep engine in good operating condition the generator should be operated under at least 50 percent load for short durations throughout the year. Fuel should be replaced or used every two months to prevent moisture condensation in the tank.