Basic types of power generators

All power generators have two main components. A motor burns fuel - usually propane, natural gas, gasoline, or diesel - to supply power, and a power generator head turns that power into electricity. Together, the motor and the power generator head comprise a standard generator.

The electricity created by a power generator is measured terms of voltage and watts. Voltage is a measure of the "pressure" of an electric current. Wattage is more like a measure of the "volume" of electricity being created. When choosing a power generator, you'll need to know the specific voltage your situation calls for, then you can pick the model that supplies enough wattage for everything you'll be running.

Voltage
In the U.S., standard household current is single phase, 120 volts. Most houses have 120/240v service, meaning they have two 120v circuits. The two are combined to provide 240v for power-hungry appliances such as electric ranges, central air conditioning, and water pumps. Many small businesses use this 120/240v service.

However, larger businesses often have different power needs. Often, they use three-phase power, which is better for running heavy-duty motors than the residential-standard single-phase service. In the U.S., three-phase power usually produces 120/208 volts or 277/480 volts. Power generators are available for all common voltages - make sure you know what voltages your business is using now and you'll be able to find a match.

Wattage
Unlike voltage requirements, which are set based on your existing circuits and electric service, wattage requirements increase with each additional appliance or piece of equipment you want the power generator to power. Choosing the right wattage is critical - we'll discuss Sizing Your Generator in the next section.

The smallest generators produce around 800 watts, while large industrial generators can produce 500,000 watts (500 kilowatts, or kW) or more. Typical sizes are around 15 to 100 kW for small businesses.

Types of power generators
There are two basic types of generators to consider: standby generators and portable generators.

Standby generators are used to offset the harmful effects of power outages: they're installed permanently as an emergency power source for your business. They are hardwired into the building's electrical system and often get fuel from city gas or propane lines. They start at around 7 kW and can easily be as large as several hundred kW.

In contrast, portable generators are used to provide power in places that don't have any, such as construction sites or other remote locations. In a pinch, they can also be used to power essential equipment during a power outage, just like standby generators. However, unlike standby generators, they're designed to be used for short periods of time - only a few hours at a stretch. As a result, they tend to be much smaller and less expensive.

Built-in fuel tanks allow them to run anywhere, and standard power outlets let you plug in ordinary extension cords. The smallest gasoline-powered portable generators are under 1 kW, and the largest reach around 15 kW. A sub-class of "towable" generators - designed to be towed to construction sites - run on diesel fuel and can be as large as 200 kW or more.