Wrong on both accounts. Technology Connections spent a while trying to figure this one out and did a fairly decent video: https://youtu.be/udNXMAflbU8

the tl;dw is "They're for manufacturing purposes" -- Alignment for when you're injection molding around them. Any other use is entirely secondary. NEMA sockets don't have any mechanism to hold onto the detent.

Heavy equipment often has a lock through designated holes in the plug. But usually not wall warts.

Nope. That hole is, similarly, only for manufacturing positioning. It's also potentially dangerous to attempt to thru-plug lock out a device: An unsuspecting individual could jam it in anyway and suddenly potentially have the other half of a phase going through them if a receptacle is loose enough or they jam the pins in.

Under OSHA 1910.147(c)(5)(ii), lockout devices must be unique:

> Lockout devices and tagout devices shall be singularly identified; shall be the only devices(s) used for controlling energy; shall not be used for other purposes; and shall meet the following requirements:

Under OSHA 1910.147(c)(5)(ii)(C)(1), LOTO must be done such that a pair of bolt cutters alone would not simply bypass the lockout:

> Lockout devices. Lockout devices shall be substantial enough to prevent removal without the use of excessive force or unusual techniques, such as with the use of bolt cutters or other metal cutting tools.

McMaster-Carr offers only a single key-in-place LOTO for NEMA plugs, specifically 5-15 which clamps around the tines. This is a secondary use of the holes used for manufacturing but does not stop someone from giving a good solid tug, which can happen.

All other OSHA-compliant LOTO systems [encapsulate the full plug](https://www.mcmaster.com/loto-(lockout//electrical-plug-lock... or otherwise [bind to the body of the plug](http://lockoutmanufacturer.com/Pneumatic-Plug-Lockout3.html) in the case of circular connectors.

Note that OSHA LOTO rules do not stop someone from chopping the end off and putting a new connector on. They are intended to provide the broadest safety in the most common of situations.

Your McMaster-Carr link seems to be pretty good evidence that such devices exist.

FWIW I'd read c1 as stating that a lockout device need not be resistant to bolt cutters, as that would qualify as "excessive force or unusual techniques".

Sure, but that was aftermarket, not a design consideration.

My understanding is that for a long time now modern sockets don't use the holes for detent and instead just rely on friction. The current ANSI/NEMA standard says that: "The hole in flat blade is optional, and it is intended for manufacturing purposes only. However if used it must be located as per dimensions shown above"

Some interesting discussion on this topic here: https://electronics.stackexchange.com/questions/11495/nema-5...