Shock-proof your jobsite

Ground-fault circuit interrupters are a good first-line defense against electrical hazards. Or, you can use an assured grounding conductor program that can help reduce the risk of ground-fault shocks.

It’s not easy being a power cord on a jobsite. As they snake along the corridors and across walkways on a construction project, there is a chance for damage every time a worker comes through the area.

Steel-toed shoes step on them; tools and supplies drag over them. Clumsy workers trip over them; users yank on them. Some users think (incorrectly) they are also for raising and lowering power tools from scaffolds and ladders.

All of these dangers put the cord’s protective coating at risk of cuts or abrasions and can stress flexible internal wires. It can also take connectors past the point of effectively insulating the electricity from the outside environment.

Combine this tough environment with wet or damp conditions, and workers are set up for some shocking results.

According to a report on ground-fault protection on construction sites by Alexis M. Herman, secretary of the U.S. Department of Labor, ground-fault electrical shock dangers are the most common electrical hazard on today’s jobsites. This story is based on this report.

How electricity escapes
If electrical conductors are exposed, there is a danger of shocks, burns or fire. If a cord’s connector is wet, the electrical current may leak to the equipment grounding conductor or worse, through the person holding the tool as the electricity tries to find the easiest path to ground.

Moisture makes a good conductor, so power can follow the outside of a cord looking for the shortest path to ground.

If the current leaking from the tool is less than one amp and the grounding conductor has a low resistance, the tool user is not likely to feel a shock. But if the grounding connector has a higher resistance, then the current that travels through the body will also increase. The report states that if the resistance to the grounding conductor is significantly greater than one ohm, even a small electrical leak is very hazardous.

Electrocution dangers to humans
According to information from the Construction Safety Council, the human body is very conductive. It’s made up of about 60 percent water and contains many electrolytes.

An outside electrical force, even as little as 0.1 amp, can short-circuit a victim’s nervous system, causing muscles to contract involuntarily.

It can even cause the heart to fibrillate, which can stop efficient blood flow. At higher amperages, the body is like a light bulb in a circuit. The body’s resistance causes heat to be generated in tissue, causing first- and second-degree burns. At extremely high voltages, the amperage going through the body can create temperatures as high as 1,800 F, literally cooking the body tissue on the cellular level.

Because of these dangers, OSHA has developed some specific electrical standards for temporary power in 29 CFR 1926.404. It lists the requirements for ground-fault circuit interrupters (GFCIs) and the components of an assured equipment grounding conductor program. Either can be used on a jobsite, with the goal of reducing the number of injuries and accidents from electrical hazards without greatly disrupting work to complete needed inspections and maintenance.

GFCIs are a first-line defense
A GFCI is a fast-acting circuit breaker that senses small imbalances in the circuit caused by current leakage to ground. In a fraction of a second, it can shut off the electricity. It protects against a ground fault, which is the most common electrical shock hazard. It also protects against fires, overheating and destruction of the insulation on wiring.

It’s also very likely to trip if the connectors and tools are wet. That’s a good thing, but can be a nuisance, so it’s best to keep the tools and connectors dry or use water-tight or sealable connectors.

Although one GFCI can be used on a circuit that serves several tools, it may be wise to use more GFCIs to prevent several tools from losing power if one cord and tool causes the trip. It may also trip if the cumulative effect of several small leaks adds up to five milliamps, or from leaks in very long circuits.

If the GFCI senses a 5 milliamp difference in the power going out vs. the power coming back to the outlet, it will interrupt the electric power in as little as 1/40 second. A GFCI, however, will not protect workers from line-to-line contact hazards, such as a worker touching two hot wires or a hot and neutral wire in each hand simultaneously.

Other preventive measures
Insulation and grounding are meant to funnel the electricity to where it should go by providing it with a path of least resistance. That’s why the grounding wire on a tool is so important. It provides a path for electricity to follow to ground.

However, a break in the ground wire may go unnoticed, creating a shock hazard. That’s why an ongoing tool inspection program can catch those hazards.

Some tools are double-insulated, which offers additional protection on the live parts of the tool, but it does not provide protection against defective cords and plugs in heavy moisture conditions.

OSHA ground-fault protection rules and regulations require employers to provide GFCIs on construction sites for receptacle outlets that are not part of the permanent building wiring. GFCI protection must be supplied on all temporary 120-volt, single-phase, 15- and 20-amp outlets on the jobsite. A GFCI circuit does not replace the need for grounding as required by OSHA under 29 CFR 1926.

Instead of using GFCIs, a scheduled and recorded assured equipment grounding conductor program covering all cord sets, temporary receptacles and power equipment connected to those receptacles can be used.

However, OSHA is very specific about the components of an assured equipment grounding conductor program. The program must be written, describing all of its components. A competent person must be identified who will implement the inspection and testing and record test results.

The inspections must occur before each day’s use. All cord sets, cap, plug and receptacle cord sets and all equipment connected by cord and plug on temporary circuits must be checked for damage or wear. Receptacles and cord sets that are fixed and not exposed to damage do not have to be inspected daily.

Tests must be completed before first use, after repair and before placing a tool or cord set back in service. If any cord or tool damage is suspected, it must be inspected. Otherwise, the records must show checks every three months. Cord sets and receptacles exposed to damage must be tested at regular intervals, at least every six months.

The tests should check for continuity of the grounding conductor on the equipment and for a proper terminal connection of the grounding conductor.

Published in the March/April, 2003 issue of Contractor Tools and Supplies magazine.

 back to top