Class1
Tools in this class are equipped with a grounding device, and all or most parts of the insulation structure have basic insulation. If the insulation is damaged, the accessible metal parts are connected to the protective earth (see grounding) or protective neutral conductor installed in the fixed wiring through the grounding device, preventing them from becoming live and thus preventing electric shock to the operator.
Class 2
The insulation structure of these tools consists of double insulation or reinforced insulation, composed of basic insulation and supplementary insulation. When the basic insulation is damaged, the operator is protected from electric shock by the supplementary insulation. Class II tools must use non-rewirable power plugs and are not allowed to be grounded.
Class 3
These tools are powered by a safety voltage power supply. Safety voltage refers to an effective value of no more than 50V for the no-load voltage between conductors or between any conductor and ground; for three-phase power supplies, the effective value of the no-load voltage between the conductor and the neutral line is no more than 29V. Safety voltage is usually supplied by a safety isolation transformer or a converter with independent windings. Protective grounding devices are not allowed on Class III tools.
Radio Interference
Single-phase series-wound motors with commutators and DC motors can cause serious electromagnetic interference to televisions and radios. Therefore, electric tools must be designed to suppress radio interference. The main measures include shielding, symmetrical connection of excitation windings, installing electrical filters, and connecting filters in a delta configuration. If necessary, small inductance coils can also be connected in series with the motor armature.
