When a human body contacts an electrified body, there is an electric current passing through the human body. It is called an electric shock to the human body. According to the cause of electric shock, the human body can be divided into direct electric shock and indirect electric shock. Direct electric shock refers to an electric shock that the body touches the charged body directly (such as touching the phase line). Indirect electric shock refers to an electric shock caused by a charged metal conductor (such as an outer shell of a leakage device) when the human body touches a normal condition and is not electrified. According to the reasons of electric shock, the measures to prevent electric shock are divided into direct contact protection, interphase contact protection. Direct contact protection can generally use insulation, shields, fences, safety distance and other measures; indirect contact protection, generally can be used to protect the ground (zero), protection, cutting, residual current circuit breakers and other measures. The residual current circuit breakers mainly provide indirect contact protection, and under certain conditions, it can also be used as supplementary protection for direct contact, so as to protect the potentially fatal electric shock.