The accessory TIMP57 has been conceived for technical departments and measuring technicians in order to measure in combination with instruments fault loop impedance / line impedance and to calculate the assumed short-circuit current, which is essential for determining the dimension of the protections provided in common industrial electric systems. The high generated test current (max. 200 A) allows carrying out high-resolution measurements (0.1 mΩ) and therefore obtaining correct and precise results, even near MT/BT transformers. TIMP57 consists of a practical and resistant suitcase structure, it has no display and it can be interfaced by RS232 serial connection to the below mentioned instruments (called Master) in order to obtain the readings. The 4-terminal measurement allows the effect of the resistance of the supplied cables, therefore no preliminary calibrations are required.