The following system is not generally used

Answer: Option C

Option A: 1-phase 3-wire
This represents a single-phase electrical system with three wires. It is commonly used for residential and small commercial applications where a split-phase system is required, providing two live conductors and one neutral conductor.

Option B: 1-phase 4-wire
This is another single-phase system, but it includes an additional ground wire (4 wires in total). It is commonly used for applications where a ground connection is necessary for safety, such as in residential distribution panels.

Option C: 3-phase 3-wire
This represents a three-phase electrical system with three wires and no neutral conductor. It is used in some industrial and commercial applications where a neutral conductor is not required, and balanced loads are expected across the three phases.

Option D: 3-phase 4-wire
This is a standard three-phase electrical system with four wires, including three live conductors and one neutral conductor. It is widely used for industrial and commercial applications, providing a neutral for unbalanced loads and additional safety.

The option that is not generally used in standard electrical distribution systems is Option C: 3-phase 3-wire. While this configuration may be used in some specific industrial applications, it is less common in comparison to the other options provided. Most three-phase systems include a neutral conductor (Option D) for flexibility and safety.

Therefore, Option C: 3-phase 3-wire is the system that is not generally used in common electrical distribution.