Work crews spin an intricate web of electrical boxes, cords and lights across a jobsite, making it easy to get caught up in some not-so-safe power grids.

Too often, temporary power gets patched in place on jobsites with inferior distribution boxes, faulty cords and make-do components. Power experts recommend using a front-to-back approach to establish a power grid that delivers adequate, safe power on the jobsite.

Get grounded

Alternating current relies on a good ground to establish a neutral on the circuit, which is essential for system balance and safety. This can be overlooked, says George Funk of J.P. Nolan. “If you don’t properly ground the circuit, you have a floating neutral. You may have 140 volts on one side and then only 100 on the other side, depending on the loads. That means tools will be running over or under voltage, causing them to overheat, burn out or be underpowered for the job they are capable of doing,” he says.

Grounding is a simple process. “Whether it is a service panel or a generator, all it takes is a 1/2" diameter 6' long copper rod driven into the ground, then connected to the panel or generator with copper wire,” says Funk.

Scott Hagen, global product manager at Woodhead/Molex concurs. “Grounding is always important, especially with generators. Poor grounding will show up with tripping ground fault circuit interrupters while workers are using tools,” he says.

Unfortunately, the most often-used brand of distribution panel is “Jury-Rigged.” “Typically, the electrical contractor will build power distribution panels, running 10-gauge Romex NM or metal clad (MC) cable to plywood panels or pedestals with GFCI receptacles,” says Rob Larrabee, sales manager at Construction Electrical Products. “We see this more in the Midwest and eastern United States. The panels may have up to 16 receptacles with up to four outlets per circuit.

“These home-built panels are usually large and not very portable, so they are rarely moved until the job is almost finished. These panels are often outfitted household-grade GFCI receptacles that don’t work correctly because of the heavy jobsite use,” Larrabee says.

Another tactic often used: temporarily wiring metal quad boxes to I- beams or other framing components of the building. “This is very labor-intensive and can easily leave workers with a limited source of power so they run cords 100' or more, which leads to premature GFCI failure and even tool loss due to voltage drop,” Larrabee says.

Power distribution takes on even more importance if the jobsite is wet or hazardous, says Hagen. “Jury-rigged electrical distribution panels are typically not built for outdoor use and usually don’t have the proper receptacles. They accomplish getting power distributed, but don’t protect against the elements. That’s not really possible with used or renewed panels and Romex cabling.”

Electricians setting up the temporary power grid need to consider anticipated loads and likely of power cord lengths at the beginning of the project and then monitor it as the job progresses, Hagen advises.

“Workers will plug into anything, anywhere, to get the power they need. If power distribution isn’t monitored as construction progresses, it soon becomes like lighting a Christmas tree, with all sorts of tools feeding off the same outlet. That’s when circuit breakers begin to pop. That’s why ready-to-use distribution bases are a good idea. They provide GFCI protection and prevent users from overloading circuits,” says Hagen.

Once the temporary system is installed, voltage should be regularly checked along the circuits’ paths, advises Funk. “Check the voltage along the circuit several times during the day. It is hard to see voltage drop, but it can occur under heavy power use. It’s also affected by how far the tool is away from the power source.

“The electrician in charge of temporary power needs to know the input voltage, the length of the cords, their gauge and what tools they’ll be running. A simple voltmeter will confirm if there is voltage drop. If it’s noticeable, run a shorter or heavier gauge cord or use a transformer/ booster to increase voltage, but that in turn will drop amperage. If the tools run slowly, voltage drop is likely the cause,” says Funk.

Think modular

Instead of relying on jury-rigged distribution panels to power jobsites, the experts recommend using purpose-built distribution panels and boxes that are weather-resistant, easy to transport and modify as job needs change.

“If you set your temporary power up in a modular format, you can easily switch out components. Nothing should be hand-wired. It should all be plug-in components. It will save time and money in the long run,” says Funk.

The electrical service to the main distribution panel should be protected in a way that prevents unqualified workers from accessing the power source, adds Hagen.

Cord sets are your weakest link

While extension cords are perhaps the most important link in the temporary electrical power chain, they are also often the weakest link in the system, says Hagen.

“Off-the-shelf cords with molded ends are easily damaged by hard use on jobsites. Regularly inspect them and replace any damaged connectors. If the cord jacket is damaged, replace the whole cord set,” Hagen advises.

Jobsites can become wet places to work and a damaged cord can create electrocution or shock hazards.

“Workers tend to use what they have at the time they need it, so indoor-rated cords sometimes get used outdoors. Workers can’t rely on duct tape over connectors to make a waterproof connection because duct tape can easily wick water into the connections,” says Hagen.

“Cord sets used on jobsites should be SOW- or SJTOW-rated and have weather-resistant connections. Damp location-rated cords should have NEMA 3 or 4 ratings. If the cord sets will be used in areas where water may collect, NEMA 6P-rated cord sets should be used,” says Hagen.

GFCI protection

GFCI breakers or outlets at distribution panels seem like the simplest way to provide ground fault protection, but the experts advise it’s better to push the GFCIs as close to the tool as possible.

“GFCIs should be located at the point before the extension cord goes to the tool,” says Larabee. Ideally, each tool should have its own GFCI. It makes identifying tools with ground-fault problems easier.

“If several tools are on the same GFCI, it will shut down all the tools running on that GFCI, and then you have to hunt to find the tool causing the problem,” says Funk. GFCIs wear out over time, especially if there are frequent voltage spikes on the circuit. Variable-volt generators and electronic devices can also shorten GFCI life, says Funk. “Today’s GFCIs are better than older models, but if they don’t trip when the test button is pushed, they should be replaced immediately.”

Temporary lighting

String lights must be supported correctly to prevent cord damage. “Zipties work well to hold the cord in place, but the connection point should be at the built-in hook or loop on the light cages, not by the cord. The lamps are designed to carry the light set’s weight. If you are using trouble lights or other temporary lighting for task lighting, use the tool’s built-in hooks to support the light’s weight,” says Hagen.

Training

It takes diligence to maintain a temporary power system, and it will be easier if all workers are trained in the system basics and of warning signs that directly affect their safety and productivity, says Hagen. “All workers should be trained in the proper set up and use of the temporary power system. It should cover overloading, the importance of grounding and ground-fault protection and cord inspection,” he says.

“Cords need to be inspected often by everyone on the jobsite. Look for wear, cuts and broken or damaged components. This is elementary, but often overlooked. It should be done before the cords come on the job and regularly while they are on the job and again when they are taken off the job,” says Funk.