Managing the Safety of Portable Electrical Appliances
Accidents with this equipment occur in a number of ways, with potentially lethal effects.
- By Rod Taylor
- Oct 01, 2006
ELECTRICITY powers the wheels of industry and commerce, but the dangers and the hazards associated with the use of damaged electrical equipment and the use of faulty electrical tools and appliances in the workplace can be costly in both human and corporate terms.
Manufacturers of electrical equipment and appliances have come to recognize that verification of performance and safe operation of products is absolutely vital, not only to comply with established safety standards, but also to ensure total customer confidence, uphold market reputation, and minimize the risk of litigation. As a result, the safe testing of electrical products on the production line has become an essential part of the manufacturing process. But what happens when electrical items leave the factory, often for prolonged "in service" use in an industrial plant, office, or construction site? It is important to identify appropriate methods for diagnosing problems such as the deterioration in the electrical integrity of products (in vending machines, for instance) or potentially dangerous faults (as can occur in a power tool or a piece of IT equipment).
It is questionable whether sufficient attention is paid to the importance of safety checking and testing the range of electrical and electronic equipment used in commercial and industrial workplaces. It is vital to ensure that enough consideration is given to the safety implications of all types of electrical portable appliances, including hand-held power tools.
The need to be ever alert to all aspects of electrical safety standards and to continuously place great emphasis on improving those standards can be conclusively demonstrated by the following facts:
- U.S. Labor Department statistics indicate an average of more than 4,000 non-disabling and more than 3,000 disabling electrical-contact, work-related injuries are recorded annually in the United States.
- OSHA records state that an average of one person is electrocuted at the workplace every day.
Records indicate a large number of these deaths and injuries are due to electrical shock from misused or faulty electrical equipment, and most could have been avoided if proper electrical checking procedures had been applied.
Hazards Linked to Portable Electrical Appliances
Portable electrical appliances are often roughly handled when moved from place to place, operate in a variety of environments, and in many instances have more arduous and onerous usage than does fixed equipment. Accidents with such equipment occur in a number of ways.
At times, faulty cables and cords could result in bare conductors being exposed to touch, ineffective ground conductors that could result in operator electrocution if the metalwork of an electrical tool or equipment is gripped, and damaged or deteriorated insulation causing leakage currents.
In the context of leakage currents, it is always worth noting that the human body reacts to relatively low levels of current. For example, a current is discernable at levels as low as 0.9 to 1.2mA. Between 15.0 and 20.0mA, the body can experience a loss of muscle control and the onset of the "let go" threshold. At 50.0mA ventricular fibrillation occurs, and at 100mA serious burns and muscular contractions occur that are so strong the thoracic muscles constrict the heart.
Obviously, there are potentially lethal effects from faulty hand-held and portable tools and appliances. This is substantiated by the fact it is estimated that up to 25 percent of all reportable electrical accidents involve the use of portable and hand-held equipment.
Section 5(a)(1) of the OSH Act states that "each employer shall furnish . . . a place of employment [that is] free from recognized hazards that are causing or are likely to cause death or serious physical harm to his employees."
Beyond that, an electrical "general duty clause" found in OSHA 1910.303 (b)(1) is the requirement that "Electrical equipment shall be free from recognized hazards that are likely to cause death or serious physical harm to employees."
To be fully assured of meeting this requirement, an employer of personnel using portable electrical appliances would have to establish safety programs that demand rigorous inspection and meaningful electrical testing of the equipment because of the recognized hazards that can occur with such equipment. Meaningful tests in this context should not predict how an item will function when conditions are not normal, but rather determine the equipment remains safe and in a condition that will not pose a hazard to the user.
For portable appliances, tests should check the integrity of the insulation, the effectiveness of grounding conductors, the operation of personnel protective devices (i.e., Ground Fault Indicators or GFCIs) and the levels of any leakage current.
OSHA is chartered to establish requirements for employers and has no jurisdiction to assign responsibilities to employees. The National Fire Protection Association set the standard for electrical requirements for employee workplaces in its NFPA 70E publication and provides a national consensus covering the "personal safety aspects" relating to electrical energy for employers, employees, and OSHA.
NFPA 70E informs employers of the need for insulation integrity, GFCIs for personnel protection, and effective grounding paths. However, the only relevant references to "testing" in the standard are:
- That all equipment grounding conductors be tested for continuity and continuous electrical paths on all cord sets and receptacles not part of the permanent wiring of a building and cord- and plug-connected equipment required be grounded.
- That each receptacle and attachment plug be tested for correct attachment to the equipment grounding conductor, which in turn must be connected to its proper terminal.
- That "safety grounds" be tested after repair or modification.
- That under the term "testing," the insulation of defined protective tools and equipment be verified.
Although these provisions are plainly stated, none of the test parameters for the acceptable "safe" resistance of insulation or methods of continuity testing for any of the above items are defined in NFPA 70E. However, by exploring the National Electric Code and OSHA document 3007, which deals with electrical standards for construction, it becomes possible to deduce the relevant parameters surrounding acceptable levels of resistance and insulation.
The NEC Code requires that, where applicable, there must be an intentionally constructed permanent, low impedances electrical path designed to safely carry current under ground fault conditions from the point of a ground fault wiring system to the electrical supply source. Additionally, in OSHA 3007 it is stated that if the resistance of the equipment grounding conductor is significantly greater than one ohm, appliances with even small leakage currents become hazardous. If the grounding conductor has a low resistance, no shock should be perceived when the leakage current of an appliance is below one amp.
On the basis of this OSHA statement, a test on the grounding conductor should therefore indicate a resistance no greater than one ohm. For safety's sake, it is ideal to operate between a margin of 0.25 ohms and 0.8 ohms.
OSHA also states that a GFCI must operate when the leakage current exceeds 5mA +1mA within a time of 0.25 milliseconds to ensure that any possibility of electrocution is eliminated.
A GFCI installed for personnel protection as required in NFPA 70E but not tested to ensure it will operate within the above OSHA-stipulated parameters cannot justifiably claim to be in a condition to meet the purpose of its installation.
Protection Against Electrical Shock
The majority of U.S. and international standards for electrical equipment require one of two independent forms of protection against electrical shock:
- Class I (Metal Case) electrical appliances, where the safety of the operator depends on the integrity of one layer of insulation and a grounding conductor that bonds all the metalwork of the equipment to ground and ensures that in the event of a fault in the equipment, any fault current is diverted to ground and not through the human body.
- Class II (Double Insulated) electrical equipment, where there is no grounding connection and the operator's safety depends on the integrity of two layers of insulation.
Ensuring these forms do not degrade and successfully maintain protection levels over long periods is the primary objective of regular electrical inspection and safety testing routines.
Portable Appliance Testers
To meet the range of safety testing requirements of portable appliances, manufacturers of electrical instrumentation have produced a wide range of portable appliance testers under the term "PATs." These testers range from very simple to operate, low-cost versions to microprocessor-controlled units capable of carrying out more complex testing.
The acceptable safe electrical levels and the parameters of the functions performed by the portable appliance testers are based on U.S. national standards (where they exist), established best practices, or on international standards where applicable. The tests identified in NFPA 70E above, for example, could be undertaken by a basic "GO/NO GO" tester capable of providing an unambiguous "Pass" or "Fail" instruction. For example, a "Fail" would indicate a resistance greater than one ohm in the grounding conductor. Such a tester would confirm whether or not there is continuity of the grounding conductor but would not provide an actual figure of the resistance of the conductor for records or subsequent comparison purposes.
More sophisticated microprocessor-controlled portable appliance testers generally provide actual figures for the resistance of the grounding conductor, insulation levels, and ground current leakage. They also undertake a load and operation test and possess the ability to store test results in an integral internal memory. Test results can be downloaded to a PC or to a printer. In addition, the majority of these testers can operate in either automatic or manual mode.
Advances in test technology and special operator features have ensured that portable appliance testers are available to help organizations with many different appliances to consider. In particular, automatic test sequencing or menu-driven operator instructions ensure the right safety tests are performed at the right time and in the correct sequence to ensure reliable results.
The latest general-purpose portable appliance testers incorporate a full QWERTY keyboard and "fast keys" integrated with the LCD to provide instant test selection with an internal memory storage capacity up to 5,000 memory locations. Besides conventional electrical safety tests, which include a ground bond test, a ground screen test, insulation, and hi pot tests, these instruments also test for touch leakage and power cords. Units also have the facility for auto or user-defined pass/fail settings and printer output for bar codes and test certificates.
Specialist testers for specific groups of products or industry sectors are also available. For example, advanced-technology safety testers have been specially developed to help tool rental companies meet their electrical safety testing responsibilities. They include compact new bench top products designed for rental stores and tool repair and appliance service firms to enable all relevant electrical tests to be carried out quickly and easily to ensure maximum customer safety.
Any electrical safety program devised for personnel operating portable electrical appliances should include a requirement to check on a routine basis that the appliances are operating within acceptable functional levels. For example, using a tester that provides actual digital readings of the safety tests undertaken enables comparisons of successive tests to help in identifying any degradation in the safe condition of an appliance that might require increased frequency of testing.
However, the successful management of such a test or maintenance schedule can only be attained if full and accurate records of test results are made at the time of testing. As a result, the capacity to record test results in specialist software programs is another area where considerable technological progress has been made in recent years.
Specialist PAT software programs are now available that are capable of building up test databases with asset management capabilities, including report printing and calendar options highlighting next test due dates to help organizations plan and manage test programs effectively.
The pressures of insurance companies, potential penalties, and litigation all encourage a greater understanding of the need to maintain the integrity of electrical products and equipment used in the workplace. To ensure the requirements of an established safety program are being met, it is essential that a tagging system be used that defines the state of the equipment at any time and displays details of inspection, test results, and whether the equipment should be withdrawn.
For those responsible for establishing safe working conditions in the workplace, a well-planned program of preventative maintenance with regular portable appliance safety checks at its core is recognized as the optimal way to protect personnel from dangerous hazards, avoid accidents, and prevent the often serious financial consequences that can follow.
This article appeared in the October 2006 issue of Occupational Health & Safety.
Electrical Safety Testing Checklist
- Establish an electrical tool, equipment, and appliance register, preferably using a safety testing software program.
- Carry out regular visual inspections.
- Determine the frequency of testing in consultation with specialist guidelines or safety advice.
- Nominate an employee with responsibility for the safety of electrical equipment and ensure he/she is fully trained.
- Ensure tests are carried out in keeping with the frequency of testing plan.
- Establish a formal recordkeeping system, file, or software.
- Commit to a regular test and inspection program.
- Determine a retest schedule well in advance.
This article originally appeared in the October 2006 issue of Occupational Health & Safety.