To be clear, would a cable with nema5-15P on one end, and a locking 30A 120v (L5-30R) connector on the other end be acceptable in most AHJ's eyes? Since it's nema5-15P on [/font]one end, would 12ga be acceptable?[/size]
This would be solely for a convenient way to plug in my amp rack contents with a single plug (all of which are nema5-15p or nema5-20p) if I don't have somewhere to patch the distro. Behind the panel are two quad-boxes of standard Edison receptacles.
I don't think there's any complaint with a 5-15P to L5-30R cable made from 12 ga. cable, since it can't be plugged into anything more than a 20A circuit. The trouble is at the rack end. It would be possible to connect a 30A feed to that inlet flange (L5-30P), and you don't have anything to limit the current at the duplexes inside to 15 or 20A. I know that sound companies have done this for years, but it doesn't make it right.
I have heard that it is allowable to use twist-locs for non-specific applications (speakers, motor control), if there is little chance of them being mixed up with the real thing, although I can't quote chapter and verse from the CEC for that. It would be better to not give the electrical inspector something easy to trip you up on if you can avoid it. Vancouver was where the CBC found out that none of their feeder cable was allowed (at Expo 86) because it didn't have "SC" markings on it. It didn't matter that the stuff had been used successfully for years.