ABOUT ELECTRICAL SAFETY

Learn about overvoltage and how you can protect yourself.

The risk of overvoltage surges is increasing as distribution systems and loads become ever more complex. Motors, capacitors and equipment for converting current, such as motor controls with variable speed, can cause electric arcs. Lightning strikes in power lines outdoors can cause extremely dangerous surges with high energy. When you take measurements on electrical systems, these surges constitute an “invisible” and mostly unavoidable risk. They occur regularly in low voltage circuits and can peak at values of thousands of volts. In order to help protect yourself against surges, safety must be built in to the test equipment.

We have specified the safety class for each instrument in texts and tables, so you can select the right level for your work.

Overvoltage category

CAT IV

Summary

Three-phase at the primary level and all cables for outdoor use

Examples

Refers to the “installation origin”, i.e. where the low voltage connection is connected to the power socket.
Current meters, primary flashover protection.
Outdoor and at the service level, service cables from pole to building, runs between meter and panel.
Air connection to detached building, ground connection with well pump.

CAT III

Three-phase distribution, including single-phase commercial lighting

Equipment in fixed installations, e.g. control equipment and multiphase motors.
Bus and feed at industrial plants.
Feeder lines and short primary voltage circuits, distribution panel units.
Lighting systems in larger buildings.
Equipment sockets with short connections to the service level.

CAT II

Single-phase plug connected loads

Equipment, portable tools as well as household and other loads.
Sockets and long primary voltage circuits.
Sockets more than 10 metres from the CAT III source.
Sockets more than 20 metres from the CAT IV source.