Safe Use of Portable Electric Tools, Cords and Generators
This month’s Tailgate is a review of some basic safety precautions to take when using portable electric tools and equipment. The focus is on prevention of electrical shock, specifically when using 120-volt AC portable electric tools, cords and generators.
To simplify the issues, it is best to break down the equipment into the following risk categories:
Category 1 – High Risk: This covers portable electric tools and cords used exclusively through temporary wiring. It also includes portable electric tools and cords whose source of power may vary from permanent to temporary – this excludes portable generators – for construction, alteration and/or repair, including painting and decorating, or that are used in wet or visibly damp areas. This type of work has the highest risk for electrical shock hazards.
Category 2 – Low Risk: Category 2 covers portable electric tools and cords whose sole power source is the permanent wiring of any building, mobile trailer, temporary building or similar structure. This type of work has minimal risk for electrical shock hazards.
Following are some definitions that we will use as part of this Tailgate:
Ground fault circuit interrupter (GFCI): This fast-acting device senses small current leakage to ground (i.e., ground fault), and detects an imbalance between the hot and neutral circuits and trips the circuit. You must use an approved GFCI per OSHA 29 CFR 1926.449.
Vehicle-mounted: This means equipment, which is normally fastened to the vehicle, and portable equipment, which is transported on the vehicle and remains on the vehicle during use.
Portable Power Tools and Extension Cords
All extension cords and portable electric tools, except double-insulated or battery-powered tools, shall have a three-wire grounded cord and plug. A GFCI may be added as an option. If a GFCI is used between the power source and the cord or tool, the manufacturer’s recommendations should be followed for inspecting and testing the GFCI.
Tools likely to be used in wet and conductive locations need not be grounded if the supplied voltage is fewer than 50 volts or if the tools are double-insulated (29 CFR 1910.304 and 1926.302).
Typically, battery-powered tools are exempt from the inspection and testing requirements as described in this Tailgate, but the best practice is to use battery-powered portable electric tools when working on a pole, from an aerial lift or on a steel tower in an energized primary area.
Double-insulated tools shall be listed by Underwriters Laboratories or the equivalent.
Tools that are not double-insulated, and tools that normally require the user to hold an exposed metal portion of the tool, shall have a three-wire tool cord and plug with the grounding wire connected to the exposed metal portion of the tool. As an additional option, a GFCI may be permanently installed at the plug end of the three-wire tool cord.
Equipment should be inspected before first use, before it is returned to service following repairs and before it is used after any incident, which can be reasonably suspected to have caused damage.
Before each day’s use, each cord set, electrical tool and piece of electrical equipment should be visually inspected by the user for signs of damage. Equipment found to be damaged or defective shall not be used until repaired, inspected, and tested and taped for re-inspection. GFCIs should be tested before use by pressing the test button on the GFCI device or following other manufacturer’s directions. These daily-use inspections typically do not have to be documented.
Portable and Vehicle-Mounted Electric Generators and Welders
The metal frames of portable generators and welders shall either be bonded to the metal vehicle frame when operated on the vehicle or shall be removed from the vehicle to be operated.
Portable and vehicle-mounted generators and welders used to supply cord- and plug-connected equipment shall meet the following requirements:
• The generator may only supply equipment located on the generator or the vehicle and cord- and plug-connected equipment through receptacles mounted on the generator or vehicle.
• The non-current-carrying metal parts of equipment and the equipment-grounding conductor terminals of the receptacles shall be bonded to the generator frame.
• On vehicle-mounted generators, the frame of the generator shall be bonded to the vehicle’s metallic frame.
• Any neutral conductor shall be bonded to the vehicle’s metallic frame.
All portable and vehicle-mounted electric generators shall be inspected and tested. Whenever inspections, tests or repairs are made, determine that the insulation between the winding and frame is intact and that the ground wire to frame connection is intact and tight.
Guidelines for Testing 120-Volt AC Portable Electric Tools, Cords and Generators
All cord sets and receptacles that are not part of the permanent wiring of the building or structure, and cord- and plug-connected equipment required to be grounded, shall be tested to ensure the following:
• Continuity of all equipment-grounding conductors shall be continuous (not applicable for double-insulated tools)
• All equipment-grounding conductors are correctly attached to their proper terminals
The following optional tests may be performed using acceptable test equipment:
• Leakage current with the tool’s motor at rest
• Leakage current with the tool running
• Leakage current with the power to the tool reversed
• Current drawn by the tool
• Short circuits, line to line
• Short circuits, line to case
• Correct polarity
Note: Dielectric or hi-pot testing is not required for the following reasons:
• OSHA and other regulations do not require it
• Testing unnecessarily exposes the worker to high voltage
• Repeated testing may damage tool insulation
If a tool or extension cord is equipped with a GFCI, press the integral test button to ensure that the self-test function works.
Suggested test equipment:
• 120-volt AC current leakage tester
• 120- and 240-volt AC current leakage tester
• Tool and appliance tester
• Continuity tester
Testing should be performed in accordance with the test equipment manufacturer’s instructions.
Calibration of the test equipment shall be performed annually or in accordance with the manufacturer’s instructions, whichever is sooner.
Generator Inspection and Testing
• Inspect the ground conductor for visible deterioration
• Test the ground wire to the frame to ensure continuity of the ground conductor
• Ensure the tightness of all electrical terminal and receptacle connections
An assured grounding program allows for non-GFCI use, but the grounds of the equipment must be inspected and proven quarterly. Typically a colored tape or tag is used to demonstrate the inspection time frame. Extension cords without GFCIs, non-double-insulated tools and portable generators that bear an expired inspection color shall not be used until they have been inspected and taped with the correct color tape.
About the Author: John Boyle is vice president of safety and quality for INTREN, an electric, gas and telecommunication construction company based in Union, Ill. Boyle has more than 28 years of experience, and has worked in nuclear and wind power generation and electric and gas distribution.