(1)Class I tool safety protection: there are grounding devices in the tool, and there are basic insulation in all or most parts of the insulation structure.
(2)Class II tool safety protection: the insulation structure of these tools consists of double insulation or reinforced insulation consisting of basic insulation and additional insulation. Class II tools must be non reconnected power plugs, not grounded.
(3)Class III tool safety protection: these tools are powered by safety voltage power supplies. The effective value of the no-load voltage between a safety voltage guide or between any conductor and ground is not more than 50V; for a three phase power supply, the effective value of the no-load voltage between the conductor and the middle line is not more than 29V. No grounding devices are allowed on type III tools.
(4)The suppression of radio interference: the single-phase series excited motor and DC motor with commutator will have serious electrical interference to the TV and radio, so the electric screwdriver should consider the interference to the radio when it is designed.