Usually the three core electrical cable (Rated Voltage: less than or equal to 35kV) adopts two-terminal-grounding model as the total current through cable three cores is zero during operation of power cable and the both ends of cable metallic shield almost have no induced voltage.
While the single core cable (Rated Voltage: greater than or equal to 35kV) won’t use the two-terminal-grounding model. The reason is that there is induced current in the metallic shield and induced voltage on both ends of cable when currents are through cable core.
The level of induced voltage is proportional to the length of cable line and the amount of currents through cable conductor. Higher induced voltage would come into being in metallic shield in the situations of short circuit faults, lightening impulse and so on. Thus it will endanger personal safety or break down cable jacket.
In addition circulating currents probably occur in the metallic shield when the both ends of single core cable are directly grounded. It’s reported that the amount of circulating currents accounts for 30%-80% currents transmitted normally by cable core. It not only lowers cable ampacity also wastes electrical energy consumption and accelerates cable insulation aging. So the both ends of single core cable should not be grounded.