Technical aspects affecting the use of insulation monitoring devices A-ISOMETER® 5.2 Connection to a disconnected IT system 5.3 Monitoring an IT system with multiple infeeds When monitoring a disconnected IT system, make sure that the measuring voltage of the insulation monitoring device can be superimposed on all live conductors. This is achieved either via the load: (Note:the windings on a motor/transformer are low resi- stance for the measuring voltage) or by means of corresponding connection of the insulation monitoring device (multi-pole link). In an IT system, only one insulation monitoring device may beactive at any one time, otherwise, the measuring voltages willgenerate mutual interference and the measurement results will be distorted. If two IT systems are working independently of one another, there must be an insulation monitoring device installed in each system. However, it must be ensured that if the two systems are coupled, only one of these devices can ever be active at any one time.
Figure 5.2 Multi-pole connection to an insulation monitoring device on a disconnected IT system Figure 5.4 Insulation monitoring in two IT systems which can be interlinked Figure 5.3 Superimposition of measuring voltage e.g. motorwindings Figure 5.5 Connection to the supply voltageFuse protection for insulation monitoring devices Annex 1.9.1 Main catalogue part 1 – 08.2007/Insulation monitoring 167