When the residual current (leakage) protection function is added to the controller, an external residual current transformer shall be used, one for each motor. SHI-ZT30 has two current specifications: rated current 500mA (current range: 50~500mA), rated current 5A (current range: 0.5A~5A), SHI-ZT100 rated current 5A (current range: 0.5A~5A).