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1/2019 | MONITOR | 1 MAGAZINE FOR ELECTRICAL SAFETY 19 1 LINETRAXX® SensorPRO residual current monitors Smart. Flexible. Future-proof. Market-driven solutions for modern applications When the power supply ensures survival Insulation fault location on board the Polarstern Additional page "Practical Expertise" at the back of the booklet for collection! Insulation fault location in unearthed systems (IT systems) | MONITOR |1/2016 Practical Page A Expertise Insulation fault location in unearthed systems (IT systems) Ifa low-resistance insulation faultoccurs between theactiveconductorsandearth in anunearthedsystem,anearth faultorshort- circuit toexposed-conductivepart willoccur. However, since the level of the residual current is lim- ited by the overall leakage capacitance of the system, neither non-permitted high touch voltage nor a risk of fire will occur. The insulation monitoring device (IMD) will report an alarm, but the power supply is usually maintained and the system will continue to operate. The action required is to eliminate the insulation fault asquickly aspossible.Buthowdo you locate the fault? In earthed systems, narrowing down the location is very simple. If a dead short-circuit to earth occurs, the short-circuitprotectivedevice closest to the locationwill trip (provided selectivity ismaintained). In the eventof a short circuit to exposed-conductive part in an electrical device, the circuit-breaker of the supplying final circuit will trip.Locating the fault is thennarroweddown to the cable system and the equipment located behind the protective device in the direction of current. Although the system is shut down until the fault is rectified, locat- ing the fault isquick inpractice. 1/2019 | MONITOR | 44 In an unearthed system: The system continues to function despite a short-circuit to exposed-conductive part, the IMD indicates an insulation fault In earthed systems:A shortcircuit to exposed- conductive part leads to a shutdown Power quality Not all power sources are the same