LSY Residual fire monitor CT

Why need to monitor the residual current and how to choose residual current transformer?

Residual current is also called leakage current (leakage current).In the absence of applied voltage, the electric current generated between metal parts with mutual insulation, or between live parts and grounded parts, through their surrounding medium or insulation surface, is called leakage current.That is, the current vector and non-zero current of each phase (including neutral line) in the low-voltage distribution line.
Leakage current will be generated in electrical devices, and very small leakage current will cause great harm and serious consequences.
Common facies interphase short circuit can produce a large current switch protection, and the human body to get an electric shock, to the aging power lines due to electric leakage and fire equipment grounding fault is caused by the leakage current, usually in 30 ma - 3 a, the value is very small, for traditional switch protection and must use of residual current monitoring and protection devices.
Residual current monitoring device (residual current transformer + control body) is suitable for AC660V TT and TN systems and is an effective measure to prevent electric shock, electrical fire and equipment damage.