Re: welding cable ampacities
Per 527.4 (B), temporary feeders can be cable assemblies, or multiconductor cords or cables of a type in table 400.4 for hard or extra hard usage. (My wording). And the handbook commentary says all tempory wiring methods have to be approved by the AHJ.
Exception to 527.4 (B): Single insulated conductors shall be permitted only for emergencies and tests and only where accessible to qualified persons (edited by me to make shorter typing).
Thats the 2002 NEC. I just looked in the 99 NEC, and Article 527 doesn't appear there.
If you use a multiconductor cord or cable assembly instead of single conductors, it can generally be used for temporary wiring (not just tests or emergencies) and access doesn't have to be limited to qualified persons.
Steve