Which of the following is NOT a type of ground fault system?

Segmented ground is not recognized as a type of ground fault system within the context of electrical distribution systems. Ground fault systems are designed to detect and mitigate faults that may occur in an electrical system, allowing for safer operation.

Ground return typically refers to a method in which the return path for electrical current is through the ground, functioning effectively in some grounding systems. Residual ground systems involve measuring the residual currents and determining if there is an imbalance, which indicates a ground fault. Zero sequence systems are a type of protection mechanism that uses zero-sequence current transformers to detect ground faults.

In this way, segmented ground does not fit into the categorization of ground fault systems typically discussed in electrical training and standards, making it the correct choice in identifying which option does not belong.