The correct answer is: A. fault occurs on the bus itself.
A single bus-bar system is a type of electrical distribution system in which all of the power lines are connected to a single bus bar. This type of system is often used in small businesses and homes.
If a fault occurs on the bus bar itself, then all of the power lines will be disconnected from the system. This will cause a complete shut down of the system.
The other options are incorrect because they would not cause a complete shut down of the system.
Option B: If a fault occurs on the neutral line, then only the power lines that are connected to the neutral line will be disconnected from the system. The other power lines will remain connected to the system.
Option C: If two or more faults occur simultaneously, then it is possible that the system will not shut down completely. However, it is also possible that the system will shut down completely. It depends on the severity of the faults.
Option D: If a fault occurs with respect to earthing, then the power lines will be disconnected from the earth. This will not cause a complete shut down of the system. The power lines will still be connected to the bus bar.