LIMIT | Everything can be measured 1
ABOUT ELECTRICAL SAFETY As distribution systems a
nd load become increasingly complex, so the risk of transient overvoltages increases. Motors, capacitors and current conversion equipment, such as variable-speed motor controllers, may cause electric arcs. Lightning strikes involving outdoor power lines can cause extremely dangerous high-energy transients. When performing measurements on electrical systems, these transients present an “invisible” and largely unavoidable hazard. They occur regularly in low-voltage circuits and can reach peak values of thousands of volts. Safety has to be built into test equipment so that you can protect yourself from transients. We have provided the safety classes for each instrument in texts and tables so that you can choose the right level for your work. OVERVOLTAGE CATEGORY IV Three-phase at primary level, all conductors for outdoor use Refers to “origin of the installation”, i.e. where the low-voltage equipment is connected to a power socket. Electricity meters, primary spark arrestors Outdoors and at service level, service lines from terminal to building, passing between meter and panel. Overhead connection with freestanding building, ground connection with well pump. ÖVERSPÄNNINGS KATEGORI II Single-phase, plug-connected loads Equipment, portable tools and household and other loads. Sockets and long mains voltage circuits. Sockets more than 10 metres from the CAT III source. Sockets more than 20 metres from the CAT IV source. OVERVOLTAGE CATEGORY III Three-phase distribution, including single-phase commercial lighting Equipment in permanent installations, e.g. inspection equipment and multiphase motors. Buses and feeds at industrial plants. Feeder cables and short mains voltage circuits, distribution panel units. Lighting systems in larger buildings. Appliance connectors with short connections to the service level. CAT IV CAT I CAT II 90 | CAT III