John,
I can't make the cord cap config out, but it looks like a 5-15 (???) I was called for an ice machine once (the same place that had the "in-use" floor boxes) that was 208V and kept tripping a single pole 20A in a downstairs panel for offices.. Someone must've gone into the crawlspace above and simply looked for anything that would make a wiggy show 208V since they pulled a leg from 2 different boxes, which ended up coming from 2 different panels on 2 different floors! the tripping breaker was a lighting ckt, the other leg was tied into a general recept ckt for 2nd floor corridors. [Linked Image]

Randy