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Do you know what OSHA has to say about electrical safety testing requirements on jobsites?
In the rugged construction site environment flexible cords that supply portable tools and appliances are all subject to hazards that can damage the cords' insulation. Hazards are also created when cord connectors, receptacles, and cord-and-plug equipment are improperly used and maintained. That's why effective testing of the electrical protection and protective devices installed on such sites is essential to ensure the safety of all the trade workers on-site.
OSHA 29 CFR 1926 404 (b) (ii) and (iii) define two means of preventing ground fault electrical shocks on jobsites — the provision of ground fault circuit interrupters (GFCIs) and an assured equipment grounding conductor program.
Provision of GFCIs
The OSHA standard for ground fault protection on construction sites requires the provision of approved GFCIs for all 120V, single-phase, 15A and 20A receptacle outlets that aren't part of a building or structure's permanent wiring and are in use by employees. A GFCI operates by sensing small imbalances in a circuit caused by current leakage to ground. For grounded equipment on a jobsite, the OSHA standard requires that the GFCI must operate when the leakage current exceeds 5mA 11mA within .25 ms to ensure that any possibility of electrocution is eliminated.
The standard, however, doesn't define any testing of the operation of the GFCI to confirm that it performs to the requirements. To ensure that a GFCI is fully effective, the test button on the device should be operated monthly, according to the U.S. Consumer Product Safety Commission. Checking the leakage current and time operation of a GFCI should be undertaken at least once a year using an approved instrument. The instrument should be capable of injecting test currents of 5mA to 500mA and display times of 0 ms to 2,000 ms to provide current and time settings to meet OSHA requirements. The test instrument should be capable of ensuring accurate test results in the shortest time possible.
Testing a GFCI to the above requirements will confirm that the device is continuously providing effective ground fault protection.
Grounding conductor program
OSHA requirements include a scheduled and recorded assured equipment grounding program that covers all cord sets and receptacles that aren't part of the permanent wiring of a building or structure, and all equipment connected by cord and plug that can be used by employees. The program has to incorporate visual daily inspections of electrical equipment in order to ascertain any external defects like insulation damage, aging, or indication of internal damage. One or more designated persons must establish and implement the program. A written program description must be made available on-site for employees.
Diligent and conscientious daily visual inspections can go a long way in eliminating faulty cords, connectors, portable appliances, and similar products, but electrical testing is also necessary to ensure that the grounding of the equipment is effective.
OSHA defines two tests that must be performed. All equipment grounding conductors must be tested for continuity, and every receptacle and attachment cap or plug must be tested for the correct attachment of the equipment grounding conductor that in turn must be connected to its proper terminal.
OSHA states that if the resistance of the equipment grounding conductor is significantly greater than 1 ohm, tools with even small leakages become hazardous. If the grounding conductor has a low resistance, no shock should be perceived when leakage current of tools is below 1A. OSHA, however, doesn't refer to the appropriate pass level for the resistance of the grounding conductor.
It should be noted that when a fault occurs in the equipment, a grounding conductor with a high level of resistance could prevent the passage of the fault current to the protective device that would disconnect the fault. It's therefore essential that a meaningful test should be capable of indicating that the resistance of the conductor is within an acceptable and safe figure.
With a lamp-and-battery or bell-and-battery arrangement, the fact that the lamp could light and the bell could sound might mean that the resistance of the grounding conductor could range from nothing to thousands of ohms. It's therefore not possible for this method to determine that the actual resistance of the conductor is within a limit that doesn't give rise to any hazardous condition that could occur, as stated earlier, with a resistance of greater than 1 ohm. In addition, a lamp-and-battery or bell-and-battery unit, which has to be wired up for each test, isn't particularly robust or compact, nor easily applied for portable testing.
Testing with a handheld, portable, compact, and robust instrument on-site requires the tester to be connected to the source of power supply and the jobsite equipment. The need for such an easy-to-operate tester is further strengthened on two counts. The first relates to the frequency with which the tests have to be performed. Tests must be performed before initial use, after repairs, and before being placed back into service. Equipment must also be tested before use and after an incident that could have been suspected to cause damage. Barring either circumstance, equipment should be tested at least once every three months.
The second factor is linked to the requirement that records must be maintained of each test taken on every separate item of equipment. The ability to state that the equipment resistance levels continued to be within a specific pass level gives greater assurance to the test results. If a fail is recorded on the tester, the item or toll concerned can be justifiably withdrawn from use.
A combination of measures is recommended to reduce ground fault electric shocks on jobsites. Safety programs should ensure that GFCIs are installed and regularly tested to demonstrate that they'll operate within the leakage current and time requirements as defined by OSHA. In addition, a grounding conductor program must be linked to the regular testing of ground conductors for electrical continuity.
In both these cases the use of appropriate test instruments will help to eliminate any user uncertainty. When danger to construction workers is the issue it's better to be safe than sorry.
Jansen is vice president of Clare Instruments U.S., Inc., Tampa, Fla.