Tutorial: Hazard and risk categories for electrical workplace safety
As the electrical work environment becomes more hazardous, the need for arc flash, electrical transient, and electrical shock protection increases. Standards are cited and advice follows for ways to lower risk.
For U.S. electrical workplace safety, the key standard is National Fire Protection Association (NFPA) 70E, Standard for Electrical Safety in the Workplace. The U.S. Occupational Safety and Health Administration (OSHA) refers to NFPA 70E for electrical safety. The preferred way to work on hazardous electrical circuits is with the power off. Equipment that could be turned on must be locked out and tagged. But some tests, such as the current tests that clamp meters perform, aren’t possible unless circuits are live.
As the electrical work environment becomes more hazardous, the need for arc flash, electrical transient, and electrical shock protection increases. For situations when a location-specific arc flash hazard analysis is not available, NFPA 70E defines the arc flash protection boundary for equipment with voltage levels between 50 V and 600 V at four feet. (See NFPA 70E section 130.3 (A)(1) for full details.) The standard names a wide variety of electrical maintenance tasks and assigns each a hazard/risk category of 0 to 4. The standard also details the kind of personal protective equipment (PPE) that must be worn when working in the various hazard/risk categories.
The NFPA standard categorizes test equipment as PPE and requires that test equipment be rated and designed for the circuits and environments where it will be used. To clarify what this means, the 2009 Edition of NFPA 70E cites American National Standards Institute (ANSI)/ISA- 61010-1 (82.02.01)/UL 61010-1, the standard first established as International Electrotechnical Commission (IEC) 61010.
These measurement categories (CAT) listed in the standards cover systems of 1000 volts or less, including 480-volt and 600-volt, three-phase circuits. They define the danger of transient voltage spikes and electrical arc flash and differentiate the severity by location, voltage level, and potential for harm. ANSI, the Canadian Standards Association (CSA) and IEC define four measurement categories.
• CAT IV is applicable to test and measuring circuits connected at the source of the building’s low-voltage MAINS installation.
• CAT III is applicable to test and measuring circuits connected to the distribution part of the building’s low-voltage MAINS installation.
• CAT II is applicable to test and measuring circuits connected directly to utilization points (socket outlets and similar points) of the low-voltage MAINS installation.
• CAT I defines non-CAT rated products that are not intended to be directly connected to the MAINS supply.
Some installed equipment may include multiple categories. A motor drive panel, for example, may be CAT III on the 480-volt power side, and CAT I on the control side.
A higher CAT number refers to an electrical environment with higher power available and the potential for higher-energy transients. A test tool designed to a CAT III standard can resist higher energy transients than one designed to CAT II standards. Within a category, a higher voltage rating denotes a higher transient withstand rating. For instance, a CAT III-1000 V test tool has superior protection compared to a CAT III-600 V rated tool.
Product designs can lower risk
Industrial and commercial electricians often work in 480 volt electrical environments that pack enormous transient surge potential—and pose a significant threat of arc flash and shock. New Fluke test tools exceed international standards for safe use in such environments, the company said. Some tools enable technicians who must test live circuits to do their jobs at a distance from electrically hazardous installations.
For example, new Fluke 381, 376, 375 and 374 current clamps and Fluke iFlex current probes are rated for use in measurement category IV environments (CAT IV 600V, CAT III 1000 V) as defined by safety standards in the U.S., Canada and Europe. The detachable display of the new Fluke 381 Clamp Meter enables technicians to see measurements remotely—up to 33 feet from the equipment being tested. Those conducting the test can see readings when the test circuit is enclosed in an equipment cabinet.
The new Fluke ScopeMeter 190 Series II handheld portable oscilloscopes are the first four-channel scopes designed for harsh industrial environments. They are rated as dust and drip-proof and are said to be the first hand held oscilloscopes safety rated for CAT III 1000 V / CAT IV 600 V environments.
- Hazard / risk categories information provided by Fluke. See also
For more on machine safety, see Cover story: Machine Safety Integration.
See the Plant Safety and Security Channel at http://www.controleng.com/channels/plant-safety-and-security.html.
- Edited by Mark T. Hoske, CFE Media, Control Engineering, www.controleng.com
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