Compact, portable generators provide power on construction and maintenance job sites that don’t have conventional power. They are essential for emergency repairs when the power is out and are one of the types of equipment needed for rescue and emergency work to restore basic services immediately after hurricanes, tornadoes, earthquakes and other disasters.

Portable generators are available in sizes to fit a variety of requirements, including operating power tools, lighting and computers and other office equipment at mobile job-site offices. One person can easily carry the smallest units by him or herself.

Electricians have a choice of portable generator models with a broad range of power output capacities. Depending on the model, both single- and three-phase power can be developed, and some units permit the use of small tools at the same time the generator is producing three-phase power.

A host of manufacturers offer portable generators. The most popular sizes are readily available at general rental centers, with equipment rental specialists stocking larger models.

“Electricians and other construction industries depend on small, lightweight, hand-carry portable generators for temporary power,” said Jim Rose, Multiquip director of product management for power equipment. “For just about any venue or site, there is likely a small portable generator available and able to meet demands for portable power.”

Multiquip distributes eight basic models of hand-carry, tube-frame type portable generators.

“The kilowatt [kW] output needed for a job depends on the type of job and number of electrical appliances used. From our product line, generators rated from 2.5 kW to 10 kW are very popular,” Rose said.

When more power is needed, larger models fill a range of temporary power needs and are still compact and easy to move around job sites. Larger units are available in trailer-mounted models, and some portable lighting units have self-contained generators.

“I believe that the single most important feature is reliability because down time costs money,” Rose said. “As for physical features, the majority of users want readily accessible power receptacles, in both 120-volt [V] and 240V configurations. Another great feature is automatic idle control, which allows the generator engine to come to an idle if there are no tools in use. If the electrician picks up a saw or other power tool and pushes the start switch, the generator will come up to full operating speed. This feature reduces fuel consumption when the generator is not actually producing power and also helps to reduce noise.”

Honda Power Equipment markets compact generator products rated from between 1,000 and 6,500 watts (W).

“Quiet, reliable and durable power is extremely important to electricians and other contractors, said Rock Reed, assistant vice president, Honda Power Equipment. “Minimal unit downtime and maintenance are vital to a productive contractor. Product reliability, fuel efficiency and cost of operation are strong considerations when purchasing or renting compact generators. Although we have not experienced drastic swings in generator size demand over the past two years, it does appear that users are very carefully evaluating their generator purchases and rentals more than ever.”

Inverter technology is one of the most important advances in compact generator equipment. It takes raw power produced by the generator and passes it through a microprocessor that provides power with a sine wave similar to alternating current from a standard household wall outlet.
Inverter technology also has allowed portable generators to substantially reduce weight and size by eliminating a standard alternator. Reed said Honda inverter models weigh 50 percent less and are one-third smaller than conventional generators.

He added that inverter models should be used to operate computers and power-sensitive testing equipment that require consistent electrical current and a stable sine wave or signal.

Reed said computers and power-sensitive testing equipment require such clean power—consistent electrical current that has a stable sine wave or signal. A computer without clean power would likely freeze, shut down or its operation would be interrupted.

“Therefore, a generator featuring inverter technology is best for powering these types of sensitive products,” Reed said.

When deploying generators on a large project, it is important to match generator with power requirements for which it will be used.

Safe Generator Operation
Use of portable generators involves serious safety risks, primarily exposure to carbon monoxide poisoning, electric shock and electrocution, and fire or explosion. The U.S. Consumer Product Safety Commission (CPSC) provides general safety guidelines for avoiding these hazards. The following safety tips are summarized from information published by CPSC.

To avoid carbon monoxide hazards:
• Never use generators inside buildings, basements, crawl spaces, or other enclosed or partially enclosed areas, even with ventilation.
• Always operate generators outdoors, away from doors, windows and vents.
• Follow manufacturer’s instructions.
• In areas where power is provided by generators, install battery-operated or plug-in (with battery backup) carbon monoxide (CO) alarms following the manufacturer’s instructions.
• Test CO alarms often and replace batteries when needed.

To avoid electrical hazards
• Keep the generator dry, and operate on a dry surface under an open, canopy-type structure.
• Dry hands before touching the generator.
• Plug appliances directly into generator or use a heavy-duty outdoor-rated extension cord. Make sure extension cords are free of cuts or tears and the plug has all three prongs, especially a grounding pin.
• Never plug a generator into a wall outlet. This practice, known as backfeeding, can cause an electrocution risk to utility workers and others served by the same utility transformer.
• Only a qualified electrician can connect a generator to a building’s wiring system, or the power utility may install an appropriate transfer switch.

To avoid fire hazards
• Do not refuel a generator while it is running. Stop and allow time to cool before adding fuel. Fuel spilled on hot engine parts could ignite.
• Always store fuel outside of living and work areas in properly labeled, nonglass containers.
• Store fuel away from any fuel-burning appliance.

Information provided by the Consumer Product Safety Commission

Reed said Honda recommends that when considering your power needs, first determine the highest power application that will be operated by the generator. When operating reactive loads (tools and other devices with electric motors), it requires as much as three times the power to start the device as it does to keep the device running. Therefore, the power required to start the capacitor motor on these applications will determine the rated power of the generator for the application. When determining the proper generator for reactive loads, three modes of operation must be considered: starting power needed, power required to run the motor once it is started and loaded power requirements necessary when the tool begins to work—that is when a saw begins to cut or a drill penetrates material.

“A generator,” Reed said, “never should be operated at its maximum power output for more than 30 minutes. Rated power, or the power that a generator can produce for long periods of time, is a more reliable measure of generator power. Typically, rated power is 90 percent of maximum power.”

Generators have long been a popular rental item. While most large electrical contracting companies own portable generators in a variety of sizes, renting is an option during peak work periods.

The current recession has reduced generator rentals for the world’s largest equipment rental company.

“Until the beginning of the recession,” said Bruce Lafky, vice president for service and maintenance at United Rentals.

“Our experience was that the demand for portable power was growing, but that reversed in the downturn. As with most equipment categories tied to construction, demand for generators has been impacted by the cycle,” Lafky said.

Even so, generators remain an important part of United Rentals, business.

“Portable generators are an important component of our fleet mix, in part because of their versatility,” he said. “We had about 6,000 generator units in our fleet at the end of 2009, which was down slightly from 2008 but still significant.”

The most popular rentals at United Rentals locations for electrical contractors are towable units ranging from 25 kilovolts (kV) to 75 kV, Lafky said. Branches typically offer generators from 1,000W through 700 kV, plus a sampling of larger units. The bulk of the units are sourced from Multiquip, Wacker and Magnum, although a number of other major manufacturers also are represented in our inventory. Some locations specialize in power and heating, ventilating and air conditioning rentals and, in addition to offering larger, more sophisticated equipment, they provide expertise to customers.

“In our experience, commercial customers—including electricians—are most interested in quiet operation, single-phase and three-phase options, and large or auxiliary fuel tanks, as well as tight voltage regulation. Safety features rank high on the list,” Lafky said.

Lafky said recent improvements to generators are better electronic controls and tighter voltage regulation.

“Manufacturers tend to be very diligent about research and development, in part because generators have broad horizontal applications in the construction and industrial markets as well as special events and home renovation,” he said.

GRIFFIN, a construction and tools writer from Oklahoma City, can be reached at