• Engine-driven generators – The generator and the engine powering the generator are often sold together as a single package or “genset.” It can be an automatic-start standby generator or a manual start (pull cord or manual key) design. Generators are sized according to a kilowatt (KW) power rating. Engine-driven generators range from large permanently mounted diesel units that are used for standby systems to small portable gasoline engine generators just large enough to power vital appliances.
• Tractor-driven generators – These generators are powered from an agricultural tractor’s power take-off (PTO) shaft. These models have a lower initial cost and are expected to require less maintenance because an engine is eliminated. Tractor-powered generators are often mounted on a trailer or on a three-point hitch mounted carrier so they can be towed to different locations to power welders or other equipment in areas remote from electrical power, or serve as a "service drop".

Whether it's a direct-connected engine-driven unit or one driven by a tractor power take-off (PTO), be sure a double-pole, double-throw transfer switch is properly installed by a licensed electrician if the generator is to be connected directly to the farm wiring. This switch disconnects the commercial electricity supplier power source (the electric power company lines) from the farm electrical wiring and prevents electricity made by the generator from flowing onto utility lines where it could electrocute members of the repair crew. The switch must have the capacity to carry the total load of the farm or building it feeds, even though the generator has less capacity. When the switch is in its second position, the generator is separately connected to only the farm’s (or building) electrical wiring. Extension cords typically connect individual equipment (freezers, portable lights) to small generators.