Re: So, what are some warning signs that a stage may be unsafe?
I'm not sure. For the record, I rechecked 400.4 does allow ST, STO, STOO, STOOW, on "theater stages" as well... that list was long and I didn't feel like retyping it all out, skipped right over those. So it doesn't prohibit thermoplastic. S, S, SC, and SJ (thought not technically allowed it's a similar material) are most commonly seen in this industry and most literature I've found list them as flame retardant while ST anything isn't. I would imagine that is because one is rubber and one is plastic.
I don't know for sure, but my guess is they are not covered by these sections because they are part of "cord and plug connected equipment." The sections pertaining to theater/live sound (520) are talking mainly about electrical supply and branch circuits. It does seem like grey area though. Forget IECs for a second though... if 520 does apply to literally everything on stage, you couldn't even have a little portable fan up there if it were equipped with an SJT cord. It also might fall under some other section that exempts cords under a certain length or current rating or something.
None-the-less, good question Silas.
