1 =Protective conductor (P.E.)  equipment grounding conductor (EGC )
2 = main equipotential bonding conductor
3 = earthing conductor, grounding electrode conductor
4 = supplementary equipotential bonding conductors, bonding jumpe
B = main earthing terminal, main earthing bar, ground bus
M = exposed-conductive-part
C = extraneous-conductive-part
P = main metallic water pipe
T = earth electrode