Can you plug one extension cord into another (daisy chaining)?

OSHA will continue to enforce the listing, labeling, or certification requirements as outlined in 29 CFR 1926.403(b)(2) - Installation and use. That provision requires that listed, labeled, or certified (i.e., approved) equipment be used in accordance with the instructions included in the listing, labeling, or certification.

For an extension cord to be considered as being used in its intended application, and therefore NRTL-approved, the employer must follow all marked warnings and limitations associated with that cord, including a warning contained on a tag affixed to the cord that provides, “Do not plug one extension cord into another.” If an employer disregards such a warning tag, it would be using the cord in a manner outside of its intended application. This would be a violation of 29 CFR 1926.403(b)(2). OSHA notes also that UL 817, Standard for Cord Sets and Power-Supply Cords, provides that an extension cord set be provided with a tear resistant warning tag.