During a fault and thus while there is a very large short circuit current flowing down the cpc, a large voltage will develop along the cpc - thus the casing of equipment A may be at half the supply voltage relative to the local potential in the extr-c-p D. So if someone touches the pipe and the casing simultaneously, they may die. By locally bonding the casing to the pipe, they will end up at much the same potential and thus no death. In this latter case, fault current is flowing down the cpc and the pipe, and thus there is a similar voltage drop along both of them.
During a fault and thus while there is a very large short circuit current flowing down the cpc, a large voltage will develop along the cpc - thus the casing of equipment A may be at half the supply voltage relative to the local potential in the extr-c-p D. So if someone touches the pipe and the casing simultaneously, they may die. By locally bonding the casing to the pipe, they will end up at much the same potential and thus no death. In this latter case, fault current is flowing down the cpc and the pipe, and thus there is a similar voltage drop along both of them.
Caption