Why does the contact resistance measurement need to be tested with a DC resistance of 100A or more?

The electrical conductivity of the circuit breaker of the switch gear plays an important role in ensuring the safe operation of the switch. The quality of the conductive properties can be reflected by the size of the conductive contact resistance. Therefore, both IEC standards and manufacturers specify that the contact resistance should be measured and that the contact resistance of the various types of switches be clearly defined. In the past, dual-arm bridges were used. Due to the voltage of the bridge, the current is relatively small. When there is impurity or surface oxidation between the moving and stationary contacts of the switch, the data dispersion of the test is large. At the same time, the bridge has poor anti-interference, so the standard stipulation must use more than 100A DC current for testing. 

Kingrun series switch (circuit breaker) contact resistance tester / loop resistance tester is widely used for measuring the contact resistance, cable wire and weld contact resistance of various electrical switches.