Transient overvoltages caused by four pole miniature circuit breakers (MCB) in three-phase circuits

Miniature circuit breakers (MCB) are ubiquitous in low voltage installations and are considered to be suitable, safe, cheap and reliable protection devices. Nevertheless, they have the potential to inadvertently cause transient overvoltages downstream because of their intrinsic construction and their corresponding erratic switching nature. Thorough AC and DC tests have been performed on a plethora of MCBs across the most prominent brands on the market. The results yield that transient overvoltages have a significant probability of occurring. Their duration can range from a few milliseconds to up to tens of milliseconds. The amplitudes of the invoked transients range from 110% up to the theoretical limit of 173%. From the tests it is shown that the switching behaviour of a MCB can be simply modelled by a state system and consequently the transient voltages can simply be derived by simple network theory (i.e. voltage division principles). Therefore, this model allows further theoretical assessment for determining performance criteria and compliance tests in the relevant product standards.