The correct answer is: A. 1-phase 3-wire
A 1-phase 3-wire system is not generally used because it is not efficient. The third wire is used to carry the return current, but it does not carry any power. This means that the system requires more copper than a 1-phase 2-wire system, which does not have a return wire.
A 1-phase 2-wire system is the most common type of electrical system in residential and commercial buildings. It consists of two wires: a hot wire and a neutral wire. The hot wire carries the current from the power source to the load, and the neutral wire carries the current back to the power source.
A 3-phase 3-wire system is used in some industrial applications. It consists of three hot wires and a neutral wire. The hot wires carry current from the power source to the load, and the neutral wire carries the current back to the power source. The three hot wires are 120 degrees out of phase with each other, which means that they each carry current at a different time. This allows for more efficient power distribution.
A 3-phase 4-wire system is similar to a 3-phase 3-wire system, but it has an additional wire called a ground wire. The ground wire is used to protect people from electrical shock. It is connected to the grounding electrode system, which is a network of conductors that are buried in the ground.
In conclusion, the following system is not generally used: A. 1-phase 3-wire.