What is the meaning of the insulation color of the electrical system fe line

Construction site electrical system, the protective zero line (PE line) insulation color is yellow and green two-color line.PE line definition: the line pulled from the grounding device is the ground PE, under normal circumstances, the trunk portion of the zero line will be passed through the smaller unbalanced current, but each phase of the zero line passed by the current and this phase of the firewire passed by the current is equal to that of the ground line is not passed by any current and ground line connected to the The metal casing of electrical equipment is not charged with potential during normal operation. Zero line and ground line can not be adjusted, if adjusted leakage protection switch will operate, cut off the power supply.