Which configuration is NOT a grounding requirement as per NEC® guidelines?

The configuration that is not a grounding requirement as per NEC® guidelines is the ungrounded delta configuration. In this type of system, there is no intentional connection to ground, which means it operates without a grounding system. The NEC does not mandate grounding for ungrounded delta systems, as their design purposefully excludes a ground reference, allowing for certain operational advantages such as reduced fault current.

This stands in contrast to configurations like corner-grounded delta systems, which require grounding at one corner to stabilize the system and allow for an effective means of overcurrent protection. Similarly, wye-connected systems typically utilize grounding to protect against transient voltages and provide a return path for electrical faults. Two-wire non-grounding systems also follow specific grounding protocols to ensure safety and reduce the potential for electric shock, further highlighting the importance of proper grounding methods in electrical systems.