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Holes in plug #72549 12/03/06 03:19 PM
Joined: Dec 2005
Posts: 152
Ann Brush Offline OP
I was looking at the pictures from C-H's plugs from aroung the world site and have the following question:

Why do many US plugs have holes in the blade near the tip, no other plus seems to have that feature. What are they for?

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Re: Holes in plug #72550 12/03/06 03:32 PM
Joined: Feb 2003
Posts: 231
RobbieD Offline

Re: Holes in plug #72551 12/04/06 12:53 AM
Joined: Dec 2005
Posts: 152
Ann Brush Offline OP
That thread doesn't seem to reach consensus either?

Re: Holes in plug #72552 12/04/06 08:44 AM
Joined: Dec 2001
Posts: 2,492
Texas_Ranger Offline
No, not really... The one thing I know for sure is that I have that old receptacle where you push in the plug and feel it lock with a "snap". So it definitely has some spring-loaded balls or similar thing inside to keep the plug in.

Re: Holes in plug #72553 12/04/06 09:24 AM
Joined: Dec 2005
Posts: 152
Ann Brush Offline OP
The dimples theory makes the most sense, the confirmation of that would be a NEMA manufacturing spec for the recepticles that indicates where a dimple should be. But I cant seem to find any SOLID evidence.

Re: Holes in plug #72554 12/04/06 09:37 AM
Joined: Aug 2002
Posts: 1,691
SvenNYC Offline
Take apart an old receptacle - the older the better. You should see the "nubs" in the spring-blade contacts in there.

Not all American plugs have those holes in the pins though.

Re: Holes in plug #72555 12/04/06 04:05 PM
Joined: May 2001
Posts: 376
frank Offline
Thats also where the inspector likes to put the red tag when he finds a non approved piece of equipment.That way you can't say you didn't see it is a $5000 fine for pluging it in.The holes and nibs just give better mecanical resistance as not all mass produced plugs are the same.Hospital grade plugs are no different than spec grade(made on the same assembly line) they are just found to be "tighter" during inspection so they get a green dot.We actualy have a gauge made by hubble to test them with

[This message has been edited by frank (edited 12-04-2006).]

Re: Holes in plug #72556 12/04/06 05:31 PM
Joined: Aug 2002
Posts: 1,691
SvenNYC Offline
The holes in the pins of American plugs come in very handy when I have a radio waiting for repairs (and I don't want to accidentally plug it in and damage it further).

Just pop a zip tie through the little holes - and you're set. Poor man's LO-TO? [Linked Image]

Re: Holes in plug #72557 12/05/06 03:09 AM
Joined: Aug 2005
Posts: 265
Sixer Offline
Here's some explanations:

And here's a plug lockout:


"Will it be cheaper if I drill the holes for you?"
Re: Holes in plug #72558 12/05/06 05:46 PM
Joined: Jul 2004
Posts: 9,575
gfretwell Online Content
We had a little hardened steel pin with a ring on the end in our LoTo kitsYou stick the pin in the plug holes, run your LoTo lock hasp between the plug and the pin, between the prongs and back down through the ring on the pin. That holds the pin in and prevents using the plug. This thing was as hard as a file so you couldn't cut it with side cutters.

Greg Fretwell


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