I am installing a circuit for a welder. The supply voltage is 208V, single phase. The input amperage is 91. The manufacturer recommends input conductors of #6. They also recommend OCPD of 150 A. I've read article 630 and all of the recommendations comply. So I will pull in #4's rather than 6's because of the length, and protect it at 150 amps. I'll get some #6 SO cord to connect to the welder. What should the attachment plug be rated? Should it be rated for the load (91 amps), the wire ampacity ( 60 amps) or the OCPD ( 150 amps)? I intend to connect it with a 60 amp plug, but only because " that's the way we always do it..."