Abstract
A practical method to test post-manufactured mechanical thermal and thermal-magnetic low voltage Moulded Case Circuit Breakers (MCCBs) is presented in this paper. Many standards pertaining to the ratings of low voltage MCCBs exist, but little literature exists on how to verify its specified rating post-manufacturing. In this work, a variable voltage over fixed cable and MCCB switch contact resistance test method is used to verify ratings. This method uses two variable transformers driven by two separate stepper motors controlled by a microcontroller with a final step-down toroid transformer. To measure the circuit breaker, trip current level an accurate Hall-Effect current sensor was used and the trip time is determined by a microcontroller-based peripheral timer. Testing was conducted on four different types of circuit breakers, namely: C6, D10, C16, and C20 in order to verify the test jig functionality with good results.