They don't serve any purpose that I can think of, but since it must cost more to manufacture plugs with them than without them they must have at least a mildly compelling reason to exist, right? And that reason probably isn't "to make it easy to attach wires to them for incredibly unsafe DIY electrical work" either, although they are handy for that.
You would think that being a person who gets paid to do things involving electronics I'd have taken apart at least one electrical outlet in my life, or at least smashed it open to see what was inside (my standard method for doing science from ages 8-31). Apparently not though, because if I had I'd know there were little leaf-spring-loaded knobs inside modern electrical sockets that lightly latch into the plug-holes when you plug something in. They don't really "lock" as much as "add a little extra force holding the plug in," so you can do things like plug into a ceiling socket without gravity unplugging you. The contacts inside an electrical socket are also tapered so they'll "grab" the plug blades a little bit, but that will eventually wear out. If you've ever tried to keep a hole-less plug plugged into an older/crappier outlet, or even a holed plug plugged into an outlet so old it doesn't have the knob assembly, you'll probably notice that they fall out much more easily (I just tested this a second ago; handily, most AC USB chargers don't seem to be made with holes in the plugs these days, probably because they're light and have no hardwired cord).
Amazingly, even Wikipedia didn't know this one. I had to go to some random techie message board to figure it out, unfortunately depriving me of the opportunity to smash open an outlet and empirically determine the answer. I might do it anyway though, just to be sure.
The answer is that there exist outlets in which there are balls that cling onto those holes for a more secure hold.
ReplyDeleteHow to remove once they cling onto those holes? Actually I am not able to remove.
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DeleteIsn't that what he just said, fuckwit?
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DeleteHave a very good Switches and Sockets blog which is really interesting and knowledgeable. I really appreciate you for this good work keeps it up. You can also find a very good blog at Switches and Sockets by Meteor Electrical
ReplyDeleteI wish there were travel adapters that would use the hole to lock the travel adapter to the plug. I live in Europe so every device bought in the us needs a travel adapter. However the prongs tend to come loose quickly and then I'll hear the sparkles.
ReplyDeleteExcellent piece of information. Basic standards living along us from ages and unfortunately mostly it is hard to find why a certain standard exists or even if it is some standard.
ReplyDeleteThe reason they have those holes is so you can install a small lock to prevent usage. For example: To keep kids from plugging in electrical items or to lock out electrical appliances for repair. This was mandated back in 1957 for safety, Lock Out-Tag Out. Many years ago you could purchase a small lock at your local grocery store that supported those cord ends. Now not so available. GP
ReplyDeleteYou can do that same trick with small zipties. That's how I LOTO 120V devices at work, at least.
ReplyDeleteUntil someone comes along thinking it was a joke, like someone was goofing around, and snips the ziptie, plugs it in and ZZAAAPPP !!! Then they figger out it wasn't a joke.
DeleteA small padlock could be used to prevent someone from using an appliance. For example your teenager is grounded, so you lock the cord on the tv, or game console. Also like mentioned above you could tag out an appliance for service.
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ReplyDeleteWow, no. The holes are there because UL requires certain tests to be done in order for power cords to be "certified". Those holes are only there because one of the UL tests involves sliding a rod through those holes to perform the pull test. If you have a plug with no holes, it is a non certified knock off. ie...Chinese fake.
ReplyDelete(I am a power cord manufacturer in North Carolina.)...and I love random trivia.
U/L only tests a small sample to certify a design and production process. They could grip the prongs with "Vise-Grip" type of clamps for their pull test instead of requiring the extra drilling step for all of the zillions of production plug prongs. It makes more sense to the electrical engineer in me that U/L would specify the "rod test" because the holes are already required for another reason, like for engaging the "gripping dimples" as ICanHasPhD suggests. The electrician/scientist in me will check out some receptacles in my shop (by unscrewing, not hammering, open!).
Delete"Gripping Dimples" didn't exist back when these little holes were first implemented. Wrong answer.
DeleteInteresting. Now that i think about it, all the hole-less plugs I have are things like USB wall chargers, e.g. no cord, so maybe they're not subject to cord pull tests?
ReplyDeleteThere are definitely leaf springs that mesh with the plug holes inside an outlet, I took one apart awhile ago out of curiosity. I wonder if they came first or they took advantage of the existing holes for the UL test.
Interesting. Now that i think about it, all the hole-less plugs I have are things like USB wall chargers, e.g. no cord, so maybe they're not subject to cord pull tests?
ReplyDeleteThere are definitely leaf springs that mesh with the plug holes inside an outlet, I took one apart awhile ago out of curiosity. I wonder if they came first or they took advantage of the existing holes for the UL test.
Leaf springs are only to make good firm electrical contact. Zero strength pushing tangentially against a hole.
DeleteNot so, because there are spherical bumps (like ball detents) which engage in the hole, as the original post mentions.
DeleteDo you know if you can permanently plug prongs into a outlet? I assume you couldn't because tripping over the cord could cause damage to an outlet. I've done a light search and find anything in codes or UL. Can anyone point me to a code or legal restriction against "locking" into a socket?
ReplyDeleteNot sure Aaron as to why you would want to do that (epoxy will do the trick of you really want to go ahead), as you're then committing that outlet to the plug in question. If anything were to happen where the plug or cord needs to be replaced (such as a frayed cord), you then have to replace the whole outlet in addition to the plug.
ReplyDeleteLegally, it depends on where you are as to what code violation (if any), such a task would constitute. Best to ask a locally licensed electrician, although odds are that they will try to talk you out of it for the sake of practicality regarding the outlet.
While it might be worth questioning if permanently affixing a plug into an existing outlet is a good idea, aren't there already situations where an item is permanently connected to the building's wiring? I know I have seen items (generally in businesses, & generally lighting) 'hardwired' into the wall. Is this possible in a home system? Or is this alleged hardwiring some sort of illusion & there's, like, a false wall it appears hardwired to (since all you see is a cord entering the wall), but on the other side it's actually a fairly easy job to 'unplug' it from the electrical system?
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ReplyDeleteElectrical 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.
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So that you can lock it out by putting a small lock on it so your entitled children can't plug in tv phone tablet etc and ckean their room like you want them to well at least that's what I use them for
ReplyDeleteThose small holes can be used to prevent a device, like a TV from being plugged in if you attach a small lock to them. A GREAT way to ensure that homework gets completed before TV viewing is allowed !!! ��
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The holes exist since the twenties, related, as old patents show, to captive ball bearings and similar holding mechanisms. Once they were there, some practices used them to lock the plug or for testing purposes. Reasons why they have not been deprecated can be related with electrical behaviors of the material: lower temperature contact from lower electrical resistance, longevity, more reliable connection also without bumps in the receptacle. All the info and even the mentioned patents in:
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ReplyDeleteI would think that the holes are to hang the cord during the manufacturing as it gets it covering dipped in the plastic outer coating
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