Suppose an installation is completely or partially out of order. The installer is called to solve the problem, and finds out that the RCD is causing the trouble. When a difference between phase and neutral occurs, the RCD trips, due to an obvious leakage to earth. Frequently tripping means a continuous leakage.
The most logical reason for this problem is an decreased insulation resistance to phase and earth. In order to detect this problem, the installer decides to perform an insulation resistance test. To do so, all cables of the installation will need to be diverted and disconnected from the installation. In addition to this the installation is equipped with high sensitive appliances and equipment. Performing an insulation resistance test will seriously damage these devices.
The customer however, wishes to continue operation or at least keep the time for the inspection as short as possible. In this example, an earth leakage clamp can be used for measuring a leakage current or differential current. The clamp can also be used for locating such currents without having to disconnect or switch off the installation. This saves a lot of time and money!