Interesting comments but: The holes have been there a LONG time... long before lockout/tagout came on the scene, however I have seen some loto devices that use the holes. The contact idea is interesting but I've never seen a receptacle with contact strips having dimples... A cleaning function is interesting...could be! Still searching!
#12830 - 08/18/0209:53 PMRe: Male attachment plug prongs
I was told back in school that a long time ago receptacles had little spring loaded balls that would engage those holes.
#12831 - 08/19/0207:48 AMRe: Male attachment plug prongs
I've got a 1970ies Sony stereo with NEMA plug and an unswitched outlet. When I push in a plug I can feel that the prongs get locked when fully inserted. BTW, I was close to using the mexican style cord. I replaced a light switch in a room without a window, so I needed some temporary lighting. The only thing I could find was an imported US table lamp with an adaptor which has been hooked up forever in our living room. When I tried to hook it up I nearly got a fit. The adaptor was as stone aged as the lamp and it wouldn't fit Schuko receptacles! Finally I pulled two (illegal) ungrounded extension cords through the appartment and hooked my lamp up. SO much about being able to stick to codes...
#12833 - 12/04/0606:13 AMRe: Male attachment plug prongs