Differentiate solidly grounded neutral and impedance-grounded neutral.

• A. Solid grounding ties the neutral to earth with negligible impedance; impedance grounding uses a resistor/reactor to limit fault current.
• B. Impedance grounding ties the neutral to earth with negligible impedance; solid grounding uses a resistor to limit fault current.
• C. Solid grounding isolates the neutral from earth; impedance grounding ties to the transformer core.
• D. Both types use a direct connection to earth with no impedance.

Answer: (A)

The main idea is how the neutral is connected to earth and how that affects fault current. In solid grounding, the neutral is tied directly to earth with essentially no deliberate impedance. That creates a very low-impedance path for any line-to-ground fault, so the fault current can be very large. The large current makes protective devices trip quickly and helps force the fault to clear, but it also can cause bigger transient stresses on equipment and larger voltage dips.

In impedance grounding, the neutral-to-earth path includes a deliberate impedance, typically a resistor or reactor. This limits the fault current to a designed, lower level. The reduced fault current lowers arc energy and can improve equipment life and reduce transient impacts, though protection schemes may rely on sensing within a smaller current path to detect the fault.

So the best description is: solid grounding ties the neutral to earth with negligible impedance; impedance grounding ties to earth through a resistor or reactor to limit fault current.