IT system refers to the power neutral ungrounded system, the exposed conductive part of all the equipment are directly grounded by the respective protective wire PE, called IT power supply system. IT system is generally three-phase three-wire system.
IT mode power supply system I means that the power side does not have a working ground, or through the high impedance ground. The second letter, T, indicates that the load-side electrical equipment is protected by grounding.
IT mode power supply system in the power supply distance is not very long, the power supply is highly reliable, good security. It is generally used in places where power outages are not allowed, or where there is a strict requirement for continuous power supply, such as power steelmaking, operating rooms in large hospitals, underground mines, and so on. In underground mines, power supply conditions are poor and cables are susceptible to moisture. The IT mode power supply system, even if the neutral point of the power supply is not grounded, once the equipment leakage, the single-phase ground leakage current is still small, and will not destroy the balance of the power supply voltage, so it is safer than the power supply neutral point grounding system.
However, if the power supply is used over a long distance, the distributed capacitance of the power supply line to the earth cannot be ignored. In the load short-circuit fault or leakage so that the equipment shell charged, leakage current through the earth to form a circuit, the protection equipment does not necessarily action, which is dangerous. Only when the power supply distance is not too long is it safer. This type of power supply is rarely seen on the site.