I am putting in the electrical runs for my home shop and got some l15-30r (3-phase 240v receptacles) because I want to run 30 amp 3 phase circuits for the maximum size machine possible. All of my three phase machines are 20 amp, so l15-20p. I got some l15-30r receptacles. They are incompatible!!! Whoda thunk it. I assumed that it would be possible to plug a 20 amp (l15-20p) into a 30 amp receptacle, since that has more than enough current capacity. I would prefer not to downgrade the runs to 20 amps. The other solution is to lop off the l15-20p connectors to put l15-30p connectors on. This should be perfectly safe, since the machine will not draw that many amps. Would that violate the NEC or common sense?