It is what we usually call the ground wire. PE wire is a conductor used to ground the exposed conductive part of the electrical device, as to whether it is directly connected to the power point of the work of the ground has nothing to do with the grounding pole (TT) or through the power supply neutral grounding (TN) does not matter, both are called PE wire.
PEN wire is a conductor with the functions of both protective ground wire and neutral wire. At present, the project is mostly used in the low voltage side of the substation to the user's power inlet between a section of the line (TN-C section of the TN-C-S).PEN line is the original neutral line is accurate, good grounding, and at the same time the need to protect the shell of the equipment is connected to the PEN line.
So, the PEN line has the grounding properties of the PE line mentioned above, and also has the properties of the N neutral line and the zero line to drive the load.
Expanded:
In accordance with the provisions of GB9089.2: the protective conductor (PE conductor) is used to meet certain needs, and any of the following components to make an electrical connection between the conductor: exposed conductive portion of the conductive part of the external conductive part of the conductive part of the external conductive part of the main grounding terminal, grounding electrode, the power supply grounding point or artificial grounding point. Neutral conductor (N conductor) is connected to the neutral point of the system and can play a role in the transmission of electrical energy conductor.
See, N is the neutral line, is the working line, in the single-phase system is also known as the "zero line"; without it, the equipment may not work properly. The PE wire is the ground wire connected to the equipment shell, without it, the equipment may be able to work, but the shell may be electrified; it can prevent electrocution accidents.
In practice, people are often connected to the "protective neutral conductor", that is, connected to the PEN line, both PE line and N line function.
Baidu Encyclopedia - PE Wire