MCB belongs to the advanced level of the nineties in the international. And they also have many merits of high protective grade(up to IP20), high breaking capacity, good reliability of sensitive action, convenient multi-pole assorting, long using life etc. They are mainly used for overload and short circuit protection within the circuit of AC 50Hz, 230V in single pole, 400V in double, three & four poles of lighting distribution system in industry & commerce. Meanwhile, they are also used un turning on or off the electric apparatus and lighting circuit under the normal condition.