isolé terre (IT)

IT networks are a network form of low- voltage networks, also known as 3- wire systems, which are characterized by increased reliability. They are therefore preferred in hospital operating theaters, mobile generators, federal railroads, and some industrial plants with hazardous areas. In IT networks, the abbreviation "IT" stands for Isolé Terre.

In these three- phase low-voltage networks, there is no direct connection between the three current-carrying conductors and the ground. Isolation is provided by an isolating transformer or by an independent power supply with its own generator or uninterruptible power supply. This ensures that no direct touch voltages can occur in IT networks.

In the event of an earth fault, no additional residual current can flow in addition to the capacitive leakage current and thus no upstream residual current circuit breakers can trip. In this case, the reference potential earth is at the voltage level of the phase. Operation is thus maintained. IT systems are thus safe against one insulation fault; the fuse protection is only triggered in the event of a second insulation fault.