1. Class I:
The tool is provided with a grounding device, all or most parts of the insulation structure have basic insulation, if the insulation is damaged, because the accessible metal parts through the grounding device and installed in the fixed line of the protective grounding (see grounding) or protection zero wire connected together, will not become live, can prevent the operator from electric shock.
2. Class II:
The insulation structure of this type of tool is composed of double insulation or reinforced insulation composed of basic insulation and additional insulation, when the basic insulation is damaged, the operator is separated by additional insulation and live body, not electric shock, class II tools must use non-reconnecting power plug, not allowed to ground.
3. Category III:
This type of tool is powered by a safe voltage supply, and the idle voltage RMS between the safe voltage guide body or between any conductor and the ground does not exceed 50V; For three-phase power supplies, the no-load voltage RMS between the conductor and the neutral line does not exceed 29V, and the safe voltage is usually supplied by a safety isolation transformer or a converter with an independent winding. Protective grounding devices are not allowed on Class III tools.
4. Radio interference:
The single-phase series motor with commutator and DC motor will have serious electromagnetic interference on TV and radio, so the power tool should be considered in the design of the interference on the radio, mainly using shielding, symmetrical connection of the field winding, setting electrical filter, filter into △ shape and other measures, if necessary, you can also connect small inductors at both ends of the motor armature.
