2. Protective grounding means that the power supply mode is TN-C, and the power supply incoming line is three fire lines and one zero line (unlike TN-S, the power supply incoming line has three fire lines and one zero line), so it is necessary to carry out protective grounding, because the ground line is also zero line, so the protective grounding becomes protective grounding.
3. Repeated grounding refers to multipoint grounding to ensure that the ground wire will not be disconnected when the power supply bureau pulls in the line.
4. working grounding is different from protective grounding. In the former case, the general signal should be grounded (for example, the neutral point of the transformer is grounded, and the negative pole of the switching power supply is grounded), so that the zero potential will not drift due to the change of the surrounding magnetic field; For personal safety, the latter should ensure that the equipment can be safely touched after leakage after grounding (the principle of protective grounding and protective zero connection is different, so it is easy to find it on the Internet, so I won't go into details).