Power up!

Select generators with enough power for the job, and connect equipment safely. Right-sizing your generator for the job means accounting for the in-rush or start-up current a tool needs when you first pull the trigger. That demand can be as much as three times the tool wattage; supplying too little power to start tools quickly leads to heat buildup, which damages tools.

by Kay Falk

Generators and temporary power boxes can cause problems with power availability and safety.

“Contractors commonly use generators that don’t have enough power for their needs,” says Colin Iwasa of Yamaha Motor Corp. “Undersizing the generator damages tools and equipment.”

Matt Leggett, of the DeVilbiss technical service hotline, agrees this is the most common mistake contractors make with on-site power. “They have the generator running equipment that requires more wattage than the generator is designed to output,” he says.

Equipment running off of a generator often demands a surge of power at startup. “This is especially true with equipment that has an inductive motor,” Leggett he says.

Tool start-up can take two to three times the amount of power needed to run it. “If the generator is undersized, it doesn’t have enough power to start tools quickly,” Iwasa says. “A tool motor that doesn’t have enough power to start quickly builds up heat. That can damage the motor, and shorten its life.”

To properly size a generator, it takes some easy math. First, look at the volts and amps listed on a tool’s data plate. Multiply them to figure the wattage required by the tool. Do the same for all the equipment you want to run on the generator at the same time. Add the different tools’ wattage and you’ll have the size of generator to buy, with one additional consideration.

“Most generators have an overall wattage rating and a surge rating,” Leggett says. “If you need a 5,000-watt generator, and you’re using tools with inductive motors, you’ll need a generator that can produce 6,000 to 7,000 watts to handle the power surge. If the generator is undersized, you can blow a breaker. For example, this happens when an air compressor kicks in and you’re already powering another large piece of equipment.”

Connections make a difference
Rob Larrabee of Construction Electrical Products (CEP) says different areas of the country use portable and temporary power differently and each method has its problems. “On the West Coast, most jobsites use spider-type boxes fed with 6-gauge cords,” he says. “Contractors can make longer runs and move the power source closer to the work. This helps reduce power tool undercurrent burnout.”

Power surges are a potential problem with spider-type boxes. “They can back-feed through the system and destroy ground fault (GFCI) devices,” Larrabee says. “You can have internal surges from high in-rush, start-stop equipment like welders and submersible pumps. External surges can occur from lightning strikes or inconsistencies in power. We find the most common mistake with spider-type box systems is the miswiring of the supply cord. This can damage the GFCI devices or even leave half the box without power.”

East Coast contractors typically build their own temporary power panels on plywood, says Larrabee. “These are hard-wired to a source and generally feed off a 10-gauge building wire,” he says. “This may force contractors to use longer extension cords to reach work, which can starve tools. “The amp capacity of a 10-gauge wire is 40 percent less than a 6-gauge wire. You can’t properly power as many tools from a panel,” he says.

To assure you have enough power, think flexibility. “The ability to move the distribution equipment efficiently to accommodate the various electrical needs of the jobsite helps ensure the proper power will be available for use,” Larrabee says. “Crew concentration moves as work progresses, so power must move with them.”

Playing it safe
Because temporary power sources and generators provide electricity, they need to be used safely. Here are some tips on how to do that:

• Ground the equipment — If the generator is used outside, follow the U.S. Occupational Safety and Health Administration (OSHA) assured grounding conductor program. “An alternative option is to use portable ground-fault cord sets,” says John Otto of Tower Mfg. Corp.

“When using portable generators for primary power, inspect the generator to see if the output receptacles for 15-, 20- or 30-amp service are GFCI protected,” he says. “If they are not, seek alternatives for ground fault protection, such as portable GFCI-protected cords sets or GFCI-protected multiple outlet boxes. All GFCIs, whether they are in a breaker, receptacle or portable cord set, must have third-party listing approval, such as Underwriters Laboratories (UL).”

• Test before use — “A damaged or miswired GFCI device may allow power to flow in the presence of a ground fault, while you think you’re protected,” Larrabee says. “Unless a test is done before plugging into a GFCI device, you may not know it’s not working until you get shocked.”

He says factors that contribute to GFCI failures include power surges from miswiring and constant overvoltage. These factors can weld contacts together within the device so they can’t open when a ground fault is present, allowing current flow.

• Use proper extension cords — Otto says you want to use the gauge of extension cord that complies with the National Electrical Code (NEC) for the power being supplied. “Use 14/3- or 12/3-gauge cord for 15-amp/125-volt service. For 20-amp/125-volt service, 12/3-gauge is best; while for 30-amp/125- or 240-volt service, 10/3-gauge is good.”

• Train people — Iwasa suggests that all people using the generator should read, understand and follow the manufacturer’s owner manuals and instructions.

Otto emphasizes that key personnel need to know how to turn off the primary power if someone is being shocked or electrocuted.

Go ahead and ask for help. “Call the manufacturer’s service center if you’re unfamiliar with any aspect of generator use,” Leggett says.

• Keep it ventilated — Run the generator in an open space. “If the generator has to be protected from the elements by an enclosure, always keep one end of the enclosure open so exhaust fumes can escape,” he says.

Published in the November/December 2003 issue of Contractor Tools and Supplies magazine.

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