According to the NEC, what should extension cords not be used as?

Extension cords are designed for temporary use and are not meant to replace permanent wiring solutions in any electrical installation. The National Electrical Code (NEC) emphasizes that permanent wiring should be installed for fixed equipment and fixtures, ensuring safety, efficiency, and compliance with electrical standards.

Using extension cords as a substitute for permanent wiring poses significant risks, including the potential for overheating, electrical fires, and voltage drops. This usage can lead to hazardous conditions due to the limitations of extension cords in handling constant electrical loads that permanent wiring is designed to support.

In contrast, the other options may reflect temporary or improper usages of extension cords but do not hold the same level of risk associated with substituting permanent wiring. For example, while extension cords can occasionally serve as temporary replacements for wiring or devices, they should not be relied upon in permanent installations, as this undermines their intended purpose and violates safety regulations outlined in the NEC.