In regard to electrical contractors assembling cord sets at construction sites, the practice is acceptable, provided the assembled cord sets are constructed in a manner equivalent to those that are factory-assembled and approved. (The same approach applies to the General Industry Electrical Standards. However, your question pertained to construction, so the remaining references are to Subpart K of Part 1926.) Criteria for determining whether shop-made cord sets meet existing electrical standards include:
1)All components must be approved for the purpose by a nationally recognized testing laboratory (1926.403(a)). Individual components must be compatible for use with the other components of the completed assembly.
2)The cord set must meet all applicable requirements of Subpart K. For example, the assembly must be marked appropriately (1926.403(g)); boxes intended for use in a permanent installation may not be used (1926.403(b)(1)(i)); cords must be connected to devices and fittings so as to provide strain relief (1926.405(g)(2)(iv)); cords passing through holes in enclosures must be protected by bushings or fittings designed for the purpose (1926.405(g)(2)(v) – fittings designed to fasten cables to metal boxes are not acceptable); and no grounded conductor shall be attached to any terminal or lead so as to reverse designated polarity (1926.404(a)(2)).
3)The cord set must be assembled by a qualified person.
4)The wiring of the completed assembly must be checked before the cord set is first used. For example, the following, or equivalent, tests should be performed:
(a) All equipment grounding conductors shall be tested for continuity and shall be electrically continuous.
(b) Each receptacle and attachment plug shall be tested for correct attachment of the equipment grounding conductor. The equipment grounding conductor shall be connected to its proper terminal.