The grounded conductor provides the return path for current in normal operation, completing the circuit. Current leaves the source on the hot conductors and returns on the neutral, so the neutral carries the load current back to the source. It isn’t meant to carry fault current to ground (that’s the function of the equipment grounding conductor and the grounding system), nor is it used to shield the circuit. Bonding to the grounding electrode happens at the service equipment, while the neutral is typically kept separate from the grounding path in a feeder. So carrying return current is the best fit for its role.

Box fill is about how much volume in a box is needed to accommodate everything inside it. You count each conductor that originates outside the box and is terminated or spliced inside as one unit of volume. All equipment grounding conductors in the box are treated collectively as one unit. Internal clamps inside the box count as one unit. If there are devices installed, their mounting yokes count as one unit per device. In a box with multiple conductors and devices, you must include all of these elements in the calculation. Therefore, the option that accounts for current-carrying conductors, the grounding conductors counted as one, and the internal clamps (and, by broader understanding, device yokes as well) is the correct choice.

Continuous loads run for long periods, so the NEC requires that the current they draw not exceed 80% of the overcurrent protective device’s rating. To apply this rule, you must size the circuit breaker so that the continuous load current stays within 80% of the breaker’s rating. In practice, that means choosing a breaker that is not oversized for the expected continuous load—the breaker rating should be such that the continuous current is at or below 0.8 times the breaker rating. The other options don’t address this requirement: a dedicated service disconnect, operating all loads at 50%, or restricting to loads on 30A or larger aren’t about the 80% continuous-load rule.

Ground-fault protection of equipment is required for fixed outdoor electric deicing and snow-melting equipment because these installations are outdoors and frequently exposed to moisture. The risk is that a fault inside the equipment could energize exposed metal parts or conductive surfaces, creating a shock hazard. Ground-fault protection of equipment continuously monitors current in all conductors and will rapidly disconnect power if any leakage to ground is detected, even if there isn’t an overload elsewhere in the circuit. This provides a fast, site-specific safety shutdown for the equipment itself, which is essential in wet outdoor conditions. Arc-fault protection targets dangerous arcing that can start fires, but it doesn’t address a ground fault that could energize equipment and shock a person. Overcurrent protection only responds to excessive current from a fault, not to a ground fault with leakage that may occur at a low level. No protection is clearly inappropriate for such exposed equipment.