Extension cords used on job sites must meet which requirement?

The correct choice is the option that specifies a three-wire heavy-duty extension cord. This requirement is crucial for job sites because three-wire cords include a ground wire, which enhances safety by reducing the risk of electric shock. This grounding provides a direct path for electricity to travel back to the ground in case of a fault, protecting workers and equipment.

Heavy-duty cords are designed to withstand the rough handling and rigors of job sites, which often involve heavy machinery and other equipment that can strain or damage lighter, less durable cords. By using heavy-duty cords, the likelihood of overheating or damaging the cord due to heavy use is minimized, ensuring a safer working environment.

In contrast, the other options do not meet these essential safety and durability requirements. A two-wire light-duty cord lacks the grounding necessary for safety, while a four-wire configuration is typically used for specialized applications like higher voltage requirements rather than standard extension use. A one-wire standard option would not provide the necessary protection and performance expected in a job site setting. Therefore, the choice of a three-wire heavy-duty extension cord is aligned with industry safety standards and practices.