Before starting each job, take a minute to check the category rating and certification label of your digital multimeter or other test tool. It's not just a good work practice--it could save your life. Each tool should conform to IEC (International Electrotechnical Commission) 1010, an international standard developed to help design test tools that will stand up to today's electrical test environment.
The front of the meter should carry a designation of its CAT (category) overvoltage rating. Some also carry the marks of independent laboratories guaranteeing they meet IEC standards. Those standards are largely voluntary, and many meters claim to meet the standards but don't. That's why the seal of an independent lab is worth the extra cost.
Ranging from Category I, dealing with low energy circuits to Category IV, covering installations with lines exposed to outdoor environments, the rigorous IEC standards are designed for safety. Meters designed to the standards can withstand hazards caused by transients and other dangers. Be sure your measurement tool category rating matches how you are using the tool, even if that means switching from meter to meter throughout the day. Here's a look at the category ratings:
Category I--typically covers electronic equipment
Category II--single-phase receptacle connected loads
Category III--three-phase distribution, including single-phase commercial lighting
Category IV--three-phase at utility connection, any outdoor conductors
Category II conditions are most prevalent, but that shouldn't lull those testing electricity lines and sources into complacency. Moving from inside a house or garage to outside or into an industrial setting, probably means dealing with Category III or Category IV. Large industrial motors are in Category IV territory.
The bottom line is matching the meter to the application. One meter doesn't fit all applications.
Rosemary Baisch is a product marketing manager with Fluke Corp. (Everett, WA). For more information, she can be contacted at email@example.com.