I found this on the osha website…
When the temporary wiring consists of shop-made cord sets, etc., using approved parts, as permitted by 1910.305(a)(2) and 1926.405(a)(2), the requirements for listing by a nationally-recognized testing laboratory do not apply.
The practice of assembling electrical extension cords is considered to be in compliance with OSHA standards, provided the assembled cord sets are assembled in a manner equivalent to those that are factory-assembled and approved. Criteria for determining whether shop-made cord sets meet existing electrical standards include:
- All components must be approved for the purpose by a nationally-recognized testing laboratory (1910.303(a)) and (1926.403(a)). Individual components must be compatible for use with the other components of the completed assembly.
- The cord set must meet all applicable requirements of 1910 Subpart S and 1926 Subpart K. For example, the assembly must be marked appropriately (1910.303(e)) and (1926.405(g)(2)(iv)); boxing intended for use in a permanent installation may not be used (1910.303(b)(1)(i) and 1926.403(b)(1)(i)); cords must be connected to devices and fittings so as to provide strain relief (1910.305(g)(2) (iii) and 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 (1910.304(a)(2)) and (1926.404(a)(2)).
- The cord set must be assembled by a qualified person.
- The wiring of the completed assembly must be inspected by a qualified person before the cord set is used initially. For example, the following checks and tests, or equivalent, should be performed:
- Determine that all equipment grounding conductors are electrically continuous.
- Test all equipment grounding conductors for electrical continuity.
- Determine that each equipment grounding conductor is connected to its proper terminal.
- Test each receptacle and attachment plug to ensure correct attachment of the equipment grounding conductor.