Which systems that supply premises wiring must be grounded?

The correct choice highlights that grounding is crucial for safety and proper functioning across a range of electrical systems. Specifically, three-wire DC systems, two-wire DC systems, AC circuits less than 50 volts, and AC systems ranging from 50 to 1000 volts require grounding.

Grounding these systems is essential for several reasons: it helps protect both equipment and personnel from electric shock hazards, prevents potential fire risks caused by faulty wiring or equipment, and ensures that electrical circuits operate effectively without interruption.

In lower voltage ranges, such as AC circuits less than 50 volts, grounding provides a safety mechanism to redirect any fault currents safely into the ground, preventing detrimental effects on users. Additionally, for AC systems between 50 and 1000 volts, grounding arrangements are mandated under various safety standards to mitigate risks associated with higher voltage levels.

By grounding all these specified systems, regulations aim to promote safety standards that effectively reduce the likelihood of electrical incidents on worksites and in residential setups.