Very often, electricians must employ portable power sources to bring electrical power to their customers.

Portable generators provide dependable electricity on construction locations where commercial power is not yet available; they light the workplace and operate tools and equipment to restore power when failures occur in commercial and industrial facilities; and they are essential for rescue and repair operations when disasters strike.

Most contractor equipment fleets include portable generators in various sizes, and generators are readily available at general rental centers and construction equipment rental specialists. Rental stores replace equipment frequently, so rental units usually are relatively new and equipped with the latest features.

Whether an electrical contractor wants a dependable, all-purpose generator to handle varied power requirements, or needs equipment with special capabilities for an unusual project, the right equipment is easy to find from the wide selection of sizes and models available.

Small generator units are powered by air-cooled gasoline engines; they are light in weight and small enough to fit in the trunk of a car. Larger gasoline and diesel models are mounted on trailers for easy towing and positioning on the job. Many are available on skids for mounting on contractor vehicles or on job sites. Liquid propane and natural gas models also are available. Larger units almost always use diesel engines.

Depending on generator model, both single- and three-phase power can be developed; some units permit the use of small tools at the same time the generator is producing three-phase power. Generator packages are designed for specific jobs such as portable light towers including both generator and self-contained fresh air blowers and heaters.

Output of generators used on construction projects varies widely, starting at 4kW and going up to large units producing as much as 5,000kW and higher. Units producing from 50 to 100kW are popular models and come with a variety of features.

“The most important generator features are those that are needed at the moment,” observed Jim Rose, MQ Power director of product management.

There are many variables to consider.

“The primary need is for generators to be flexible in design and to allow for multiple voltage taps and output currents,” Rose continued. “Site requirements can vary and the capability of the power equipment to handle various requirements is also very important. Engine emissions and noise requirements are important considerations, because in some areas, there are very stringent limitations placed on both of these environmental issues.”

Their basic function—producing electrical power—has not changed over the years, but current generator models are more compact, lighter in weight, more powerful for their size, produce cleaner power and have convenience features that make them much easier to use than earlier generations. Current models require little maintenance and provide dependable, trouble-free service without much attention—something equipment users appreciate in any product. Regular maintenance basically is servicing the engine, and new engines are designed to run for longer between oil and filter changes.

The most significant application for today’s generators is to operate computers and other power-sensitive electronic equipment and that requires generators that provide “clean” power.

While tools and lights powered by a generator may be unaffected by slight AC power fluctuations, such variations can interrupt a program in operation, causing data loss or a sudden shutdown. Clean power that comes with a stable, consistent sine wave avoids such problems and reduces the risk of damage to equipment.

Here are observations and tips about today’s generator products from representatives of several generator manufacturers:

Derwin T. Pepper, product manager for Generac Power Systems Inc.’s air-cooled division: “For job site applications, high surge or maximum Watts is probably the No. 1 requirement for meeting the demands put on a generator. Multiple tools connected to the generator will be started and stopped with everything running at once or, worse, all starting at once. The electrical load initially could be far greater than the load placed on the generator when the tools are actually in operation. Automatic idle control saves on fuel when the capacity of the generator is not being fully utilized. Automatic voltage regulation is highly desirable to prevent damage from voltage spikes. It helps maintain a clean power output and reduces the need for line filters which ‘clean’ the generator’s output voltage quality.”

Ray Habic, CEO of Gillette Generators: “Demand for portable generators has increased because of the kW range of products available. Portable power at the household level for security purposes has become extremely active over the last few years. Product improvements include the reduction in size and weight per kW output. Sound levels have been reduced by better engine mufflers and enclosures on some models. Units today must generate clean power, harmonic distortion of power sine wave below 10 percent to not affect microprocessors on electronic equipment.”

Tom Pernice, generator marketing and planning manager, Honda Power Equipment, American Honda Motor Co. Inc.: “Perhaps the most important factor in selecting a generator is understanding the power requirements of the tools and equipment being used, and properly matching the size of the generator to those requirements. Honda and other manufacturers have Web site guides to educate customers about how much power various tools draw. Inverter technology now being offered provides quieter, lighter, more compact and fuel-efficient generators that deliver cleaner power output. For operating computers and electronic equipment, the most important thing to look for is regulated power output. Inverter technology in particular delivers power with sine wave distortion of less than 2.5 percent—comparable to a wall outlet.”

Al Prosser, industrial sales and marketing manager, Katolight Corp.: “Portable generators are not just for new construction anymore. We hear about new uses with every new customer. Models today are more consumer friendly, produce reduced emission levels, are quieter and have digital controls for operator ease. In the future, we will see more importance put on emissions of diesel engines.”

Ralph Schuh, national service manager, Kohler Rental Power: “Today’s generators are now more quiet than before, and much more fuel efficient, while overall size is more compact. Some of the most common features added over the last few years include multiple voltage reconnect switches, remote starting and the capability to be synchronized with other generators or a utility grid. We will see portable generators become even more quiet and be available with even lower exhaust emissions than what is available today. Future models will likely be easier to maintain. There will also be a higher demand for alternative fuels such as biofuel, fuel-cell powered generators and microturbines.”

Jim Rose, director of product management, MQ Power: “Engines on today’s portable generators are smaller, more fuel-efficient and provide this power with lower overall emissions. Horsepower-to-weight ratios are better. Noise control is a very important consideration, and some of today’s generators are much quieter than they were even a year ago. We will experience continued improvements in the area of electronic fuel control systems and generator control systems. Engines will become even more fuel-efficient. On Jan. 1, 2006, new EPA standards will usher in the use of ultra-low sulfur diesel fuel.“

Charles Hampton, product line manager, Porter-Cable: “Electricians want generators with sufficient power, reliability, low maintenance and portability. Engine and alternator quality are the primary determinants of reliability and maintenance issues. Brushless alternators with all-metal housings require less maintenance. Hour meters are important for scheduling engine maintenance, and idle control reduces noise, fuel consumption, pollutants and increases generator life. Lift kits are helpful for loading and unloading. The quality of the electricity produced is very important for electronic equipment; low THD is very important. ‘Dirty’ power can interfere with electronics and shortens tool life due to increased heat. User ergonomics are improving in the areas of panel layout and portability kit design. GFCI protection will become increasingly important as will noise control.”

Mark Conrardy, sales engineering manager, Wacker Corp.: “Features contractors find most important include duplex receptacles with ground-fault interrupters to provide protection for operators, large fuel tanks for long run times and auto idle controls to bring the engine down to idle when tools are not being used. The trend continues to make units smaller, lighter and quieter. Alternative fuels are always being explored by engine manufacturers, particularly for machines that need to run for long periods of time.”

Timothy Heinen, regional sales manager, WINCO Inc.: “Generators for the contractor market are built for heavy-duty use and are better suited for the job than their predecessors. Reliability is critical for contractors and generator manufacturers continue to develop equipment that is more durable with stronger components and structural support. Modern overhead valve engines provide excellent horsepower-to-weight ratios, and fuel efficiency has improved significantly. Most industrial line generators provide GFCI receptacles for operator safety and also provide for twist lock connections to prevent cords from pulling out. As contractor needs change, generator manufacturers will work to provide features that meet their new work requirements. Adapting to the market by providing generators that can run a wide range of equipment from a single generator will provide efficiencies for the contractor. Providing equipment that produces clean power will become more commonplace and meeting emission and noise standards will provide new challenges.” EC

GRIFFIN, a construction and tools writer from Oklahoma City, can be reached at 405.748.5256 or