Why Do U.S. Electrical Plugs Have Holes in the Blades?
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2. Electrical devices can be "factory-sealed" or "locked-out" by the manufacturer or owner using a plastic tie or a small padlock that runs through one or both of the prong holes. Construction projects or industrial safety requirements may require this type of sealing. For example, a manufacturer might apply a plastic band through the hole and attach it to a tag that says, "You must do blah blah blah before plugging in this device." The user cannot plug in the device without removing the tag, so the user is sure to see the instructions.
3. There also is a small savings in raw materials (metal) for the manufacturer of the actual plug prong. Every little bit helps!
It has been reported that really old outlets used captive ball bearings and coil springs for the detent, but today it is done with a bump and springy copper contacts.
https://home.howstuffworks.com/two-flat-prong-plug-holes.htm
My suspicion was the third one, and I suspect that was the original reason manufacturers did it. It's likely done now because of the machines that make plugs expecting those holes.
https://www.homedepot.com/p/15-Amp-Stay-Plugged-Cord-Replace...
I've never seen anything else similar.
I'm curious on the design of "hospital grade" plugs as that wasn't in his survey and I know that they are designed for higher retention force than commercial or residential applications.
#1 is ruled out as he takes apart a number of plug receptacles, from “cheap” to “heavy duty” and “commercial grade”, none of them sport the bumps you’re describing. He also points out that not all plugs have holes (using an ikea timer as an example), and observes that most plug-in receptacles don’t offer the kind of resistance one might expect if such bumps existed.
#2 and #3 are closer to the mark.
Apparently the holes are optional according to a standards body called NEMA (https://archive.org/details/NEMA-WD-6-2016/page/n24/mode/1up) and are generally intended for use in the manufacturing process.
“Hole in flat blade is optional, and is intended for manufacturing purposes only.”
See 13:30 in the video for an example.
But, this is the third time in as many months that a youtube video suggested to me has appeared on HN. It's clear that my interests (and YT suggestion algorithm) aligns with that of many HN readers.
It's _more_ interesting that HN is, in very small doses, infiltrated by megacorp algorithms. Promoted content subsuming independent discovery. Of course, 'subsuming' is too strong a word, so don't take it literally.
Look around at your high power appliances, exactly all of them will have holes in the prongs. There must be a reason don't you think?
When you are operating near the threshold for the maximum allowable current draw on a single circuit (nominally 15A in USA), this additional power loss can make your device or product fail certification.
This feature is called self cleaning contacts. It is a well known technique in the connector world. Which this tuber is not a part of.
You seem to dislike people who create content on YouTube but this video seems well sourced.