Electric tools are divided into three categories according to the way of electrical protection:
The first type of tools: that is, ordinary electric tools with a rated voltage exceeding 50V. The first type of electric tools not only rely on basic insulation to prevent electric shock, but also contains an additional safety precaution. The method is to connect the accessible conductive parts with the protective conductors installed in the fixed circuit, so that the accessible conductive parts do not become charged bodies in the accident of basic insulation damage. For tools equipped with non-reconnectable power plugs, the grounding terminal in the tool must be connected to the core wire of the flexible cable or cord for protective grounding.
The second type of tools: that is, the electric tools whose insulation structure is all double insulation structure, and its rated voltage exceeds 50V. The double insulation structure is double insulation or reinforced insulation or a combination of both insulation forms. In addition to basic insulation, double insulation has a separate layer of additional insulation. When the basic insulation is damaged, the additional insulation will separate the operator from the charged body and prevent electric shock. Reinforced insulation is to strengthen and improve the basic insulation performance, so that it has the same dielectric strength and mechanical strength as double insulation, and thus has a considerable safety protection effect.
Three types of tools: safety voltage tools, whose rated voltage does not exceed 50V. The protection against electric shock relies on the power supply from the safe voltage and the inside of the tool will not generate a voltage higher than the safe voltage. The electric shock protection of the three types of tools adopts reliable basic insulation, the power supply is insulated from the ground and the so-called triple protection of ultra-low voltage below 50V, so that the tools have higher safety performance. The second and third types of tools can protect the electrical safety and reliability during use, and no protective grounding or protective zeroing is allowed.