Fluke 179 Fluke Multimeters - ABCs of Multimeter Safety Multimeter Safety and - Page 3

location... It's not just the voltage level In Figure 1, a technician working on office equipment in a CAT I location could actually encounter dc voltages much higher than the power line ac voltages measured by the motor electrician in the CAT III location. Yet transients in CAT I electronic circuitry, whatever the voltage, are clearly a lesser threat, because the energy available to an arc is quite limited. This does not mean that there is no electrical hazard present in CAT I or CAT II equipment. The primary hazard is electric shock, not transients and arc blast. Shocks, which will be discussed later, can be every bit as lethal as arc blast. To cite another example, an overhead line run from a house to a detached workshed might be only 120 V or 240 V, but it's still technically CAT IV. Why? Any outdoor conductor is subject to very high-energy lightning-related transients. Even conductors buried underground are CAT IV, because although they will not be directly struck by lightning, a lightning strike nearby can induce a transient because of the presence of high electro-magnetic fields. When it comes to Overvoltage Installation Categories, the rules of real estate apply: it's location, location, location... (For more discussion of Installation Categories, see page 6, "Applying categories to your work.") Independent testing Independent testing is the key to safety compliance Look for a symbol and listing number of an independent testing lab such as UL, CSA, TÜV or other recognized testing organization. Beware of wording such as "Designed to meet specification ..." Designer's plans are never a substitute for an actual independent test. How can you tell if you're getting a genuine CAT III or CAT II meter? Unfortunately it's not always that easy. It is possible for a manufacturer to self-certify that its meter is CAT II or CAT III without any independent verification. The IEC (International Electrotechnical Commission) develops and proposes standards, but it is not responsible for enforcing the standards. Look for the symbol and listing number of an independent testing lab such as UL, CSA, TÜV or other recognized approval agency. That symbol can only be used if the product successfully completed testing to the agency's standard, which is based on national/international standards. UL 3111, for example, is based on IEC 1010. In an imperfect world, that is the closest you can come to ensuring that the multimeter you choose was actually tested for safety. What does the CE symbol indicate? A product is marked CE (Conformité Européenne) to indicate its conformance to certain essential requirements concerning health, safety, environment and consumer protection established by the European Commission and mandated through the use of "directives." There are directives affecting many product types, and products from outside the European Union can not be imported and sold there if they do not comply with applicable directives. Compliance with the directive can be achieved by proving conformance to a relevant technical standard, such as IEC 1010 for lowvoltage products. Manufacturers are permitted to self-certify that they have met the standards, issue their own Declaration of Conformity, and mark the product "CE." The CE mark is not, therefore, a guarantee of independent testing. Tool Tip Non-contact voltage detectors are a quick, inexpensive way to check for the presence of live voltage on ac circuits, switches and outlets before working on them. 1. Verify the voltage detector function is working properly. 2. Make sure the detector is rated for the level of voltage being measured and is sensitive enough for your application. 3. Make sure you're grounded (through your hand, to the floor), to complete the capacitive voltage connection. Use either a voltage detector "wand" or a DMM with non-contact measurement built in. This meter has a built-in non-contact voltage tester. ABCs of multimeter safety Fluke Corporation