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#72549 - 12/03/06 02:19 PM Holes in plug  
Ann Brush  Offline
Joined: Dec 2005
Posts: 152
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?

Work Gear for Electricians and the Trades

#72550 - 12/03/06 02:32 PM Re: Holes in plug  
RobbieD  Offline
Joined: Feb 2003
Posts: 231

#72551 - 12/03/06 11:53 PM Re: Holes in plug  
Ann Brush  Offline
Joined: Dec 2005
Posts: 152
That thread doesn't seem to reach consensus either?

#72552 - 12/04/06 07:44 AM Re: Holes in plug  
Texas_Ranger  Offline
Joined: Dec 2001
Posts: 2,404
Vienna, Austria
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.

#72553 - 12/04/06 08:24 AM Re: Holes in plug  
Ann Brush  Offline
Joined: Dec 2005
Posts: 152
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.

#72554 - 12/04/06 08:37 AM Re: Holes in plug  
SvenNYC  Offline
Joined: Aug 2002
Posts: 1,691
New York City
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.

#72555 - 12/04/06 03:05 PM Re: Holes in plug  
frank  Offline
Joined: May 2001
Posts: 376
windsor ontario canada
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).]

#72556 - 12/04/06 04:31 PM Re: Holes in plug  
SvenNYC  Offline
Joined: Aug 2002
Posts: 1,691
New York City
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]

#72557 - 12/05/06 02:09 AM Re: Holes in plug  
Sixer  Offline
Joined: Aug 2005
Posts: 265
Here's some explanations:

And here's a plug lockout:


"Will it be cheaper if I drill the holes for you?"

#72558 - 12/05/06 04:46 PM Re: Holes in plug  
gfretwell  Offline

Joined: Jul 2004
Posts: 9,135
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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