The performance of the conductive circuit of the circuit breaker is important to ensure the safe operation of the switch. The pros and cons of the conductive performance can be reflected by the size of the resistance of the conductive loop. Therefore, the IEC standard and the manufacturer have stipulated that the loop resistance should be measured, and there are clear specifications for the loop resistance of various types of switches. The loop resistance tester is a testing instrument meets the requirements of GB50150-2006 and DL / T 845.4-2004 regulations. It is widely applicable to the measurement of contact resistance, loop resistance, cable, wire, and weld contact resistance of various electrical switches.