The execution of manual labor takes a lot of time. Considering this problem, many manufacturers have designed some electric tools that can improve work efficiency. Although manual operation is still required, it greatly reduces the workload.
Class I: There is a grounding device in the tool, and all or most parts of the insulating structure have basic insulation. If the insulation is damaged, since the accessible metal parts are connected to the protective grounding (see grounding) or protective neutral conductor installed in the fixed line through the grounding device, they will not become live objects, which can prevent the operator from getting electric shock.
Class II: The insulating structure of these tools consists of double insulation or reinforced insulation consisting of basic insulation and supplementary insulation. When the basic insulation is damaged, the operator is separated from the charged body by the additional insulation to prevent electric shock. Class II tools must use non-reconnectable power plugs, and grounding is not allowed.
Class III: These tools are powered by a safe voltage source. The rms value of the no-load voltage between the safety voltage conductors or between any conductor and the ground shall not exceed 50V; for three-phase power supplies, the rms value of the no-load voltage between the conductors and the neutral line shall not exceed 50V
29V. The safety voltage is usually supplied by a safety isolation transformer or a converter with separate windings. Protective grounding devices are not allowed on Class III tools.