These tests should be made to the system put into service and repeated, then, modifications, repairs or extensions of an electrical installation. The installer has to demonstrate that the installation meets the requirements regarding protection of human beings, animals and electronic equipment 1. Let’s see now what weight has measurement of resistance of insulation within the mandatory testing and to what extent the connected consumer installations or surge protectors can distort the results of the test. In general terms, with the insulation measurement, the owner or user of the installation gets data about the security status of the installation. If the resistance is too low the cables are subjected to loads excessive that they can become the focus of a fire. Just this fact was that caused insurance companies to impose periodic measurements of insulation for industrial electrical installations. But what means a low insulation resistance and how we can detect it? Also here the norm (DIN VDE 0100 part 610) is very explicit.
Measurement to apply voltages and insulation resistances allowed are indicated in table 1. As seen in this table, in installations with a nominal voltage of 230/400 V insulation measurement is performed with a DC voltage of 500V. The resistance between the points described below has to be exceeding 0.5 MW, taking into account interference arising from the capabilities of the cables are excluded when measuring on direct current. The measuring device must comply too, as it is logical, the requirements of the standard DIN VDE 0413 part 1. Now it is important knowing between what drivers has the measurement. Again (we find the answer in the norm, which establishes the following: to) between the active phases (L1, L2, L3) and the protective conductor (PE).
(b) between the neutral (N) and the protective conductor (PE). (c) between the active phases (L1, L2, L3). The insulation resistance must be carried out without a network connection, but consuming facilities may follow connected if the values provided in the preceding table are met. Otherwise it must be disconnected consuming the network facilities to carry out the test. However it is important to check if electrical devices with electronic or sensitive components that can be seen are connected to the circuit to be tested affected by the test voltage measurement to apply voltages and insulation resistances allowed table. Rated circuit voltage test voltage V minimum resistance value of insulation protection or control of low voltage 250 MW circuits 0.25 nominal voltage less than 500 V, if it is not protection or reduced control circuits voltage 500 0.5 more than 500 rated voltage 1000 V 1.