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#103684 - 10/28/02 10:09 AM ECN Violations Photo Forum  
Joe Tedesco  Offline
Joined: Oct 2000
Posts: 2,749
Boston, Massachusetts USA
Plug holes???

I have a question regarding cord plugs, and meter stab blades, why do they have the holes in them?

Why not just a solid blade??

Got to be a reason, as they say for White Castle burgers

The Holes are extra!

[This message has been edited by Joe Tedesco (edited 10-28-2002).]

Joe Tedesco, NEC Consultant

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#103685 - 10/28/02 10:08 PM Re: ECN Violations Photo Forum  
HotLine1  Offline

Joined: Apr 2002
Posts: 6,853
Brick, NJ USA
I'll take a shot. Seems this subject was a thread, or a spin on one recently.
Best reasoning that I remember from those posts was something to the effect of "the hole helps to 'clean' the contact surfaces of the receptacle". Sound reasonable????

PS: Don't remember who posted that reply thou.



#103686 - 10/29/02 06:17 AM Re: ECN Violations Photo Forum  
Texas_Ranger  Offline
Joined: Dec 2001
Posts: 2,399
Vienna, Austria
Some NEMA receptacles have "nipples" on the contacts, which lock through the holes, making sure the plugs stays in.

#103687 - 10/29/02 09:11 AM Re: ECN Violations Photo Forum  
jdevlin  Offline
Joined: Aug 2002
Posts: 402
welland ontario canada
Could it be part of the manufacturing proccess? The hole are there to hold or align the spade as it is assembled.

#103688 - 10/29/02 10:56 AM Re: ECN Violations Photo Forum  
seeks  Offline
Joined: May 2002
Posts: 25
bufalo, ny 14228
My impression is that it is a materials and weight issue. An engineer did the calculation for the required square inch contact requirement, and they make sure there is JUST enough material to meet the requirement. The "holes" can then be recycled and reused. Plus, the blades now weigh less due to the removed material resulting in lower shipping costs due to the lower weight of each individual piece. Probably just some bean-counter figuring how much $$ they will save in both materials and shipping. (i'm sure it's at least a penny apiece!!)


#103689 - 10/29/02 03:46 PM Re: ECN Violations Photo Forum  
SvenNYC  Offline
Joined: Aug 2002
Posts: 1,691
New York City
From the website:

"1. If you were to take apart an outlet and look at the contact wipers that the prongs slide into, you would find that they have have bumps on them. These bumps fit into the holes so that the outlet can grip the plug’s prongs more firmly. This detenting prevents the plug from slipping out of the socket due to the weight of the plug and cord. It also improves the contact between the plug and the outlet.

"2. Electrical devices can be "factory-sealed" or "locked-out" by the manufacturer or owner using a plastic tie or a small padlock through one or both of the plug 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 tag.

"3. There also is a small raw materials (metal) savings to the manufacturer of the actual plug prong. Every little bit helps!

"It’s 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."


OK. Here's my take on these things:

As to #1: It depends on the outlet. Some just have two spring-action blades that grip the sides of the plug pin. So you don't need the holes.

#2: I've seen such locks in safety supplies catalogues. It's usually meant for items that are being repaired on-site. The lock's bolt goes through the holes in the plug and renders it "unpluggable."

For instance, you tag out the plug on the photocopier so that Secretary Maude doesn't accidentally say "hey who unplugged the Xerox?", proceeds to plug the thing in and electrocute Repairman Mitch.

As far as #3 goes...I have my reservations about that one. Most likely the holes have something to do with the manufacturing process. As JDevlin says, some tooling at the factory aligns the blades prior to molding the rubber or plastic around them.

As far as the little captive ball bearings cited in the excerpt above, I've found this to be true in some modern-day receptacles.

Last year I went to a supermarket here in Chinatown and bought an off-brand Chinese-import Nema 1-15R (notice I didn't say 5-15) receptacle strip.

Upon dissasembly of this chintzy piece of *#@&, I found a tiny spring-loaded ballbearing held in place against the plastic housing in each slot.

Now that we're on the topic of China, the "official" non-grounded plug configuration is the NEMA 1-15. China uses 220 volts/50 Hertz and Australian style
[/ \] plugs for grounded devices.

Two-prong plugs for the domestic Chinese market tend to have no holes in the blades. I've got some small "gray-market" appliances (like a beard-trimmer recharger and a small hot glue gun) at home with such plugs and they do tend to slip out of some wall sockets much more easily.

This is probably more than any of you wanted to know... [Linked Image]

#103690 - 10/29/02 05:15 PM Re: ECN Violations Photo Forum  
Bjarney  Offline
Joined: Apr 2002
Posts: 2,527
West-Southern Inner-Northeast ...
A bit off topic, but for those occasionally snot-nosed IT dorks and their precious bits, a good anti-pullout cord cap is a Hubbell 5280C, on page 15 of

[This message has been edited by Bjarney (edited 10-29-2002).]

#103691 - 10/30/02 11:29 AM Re: ECN Violations Photo Forum  
SvenNYC  Offline
Joined: Aug 2002
Posts: 1,691
New York City
Interesting!! How does it work? Does the little peg at the bottom of the cap screw into the wall plate screw-hole?

Leviton has an extension-cord receptacle that has a spring-loaded lock that goes through the holes in a cap. That way it doesn't pull out. To release it, you press a button on the side to retract the pegs. Won't work with those Chinese plugs, though :-D

#103692 - 10/30/02 02:08 PM Re: ECN Violations Photo Forum  
Bjarney  Offline
Joined: Apr 2002
Posts: 2,527
West-Southern Inner-Northeast ...
Sven -- Pardon me for not elaborating. The 5280 cord caps have a nylon-capped thumbscrew diagaonally through the U-ground pin. If the ground pin is down [the little face] it's likely a bit hidden and may be more tamper proof.

They are useful where a janitor unplugs a server [having a "fat" OC48 fiber circuit to the rest of the planet] to power his floor waxer. {That really happened.}

Then there was the owl-shift security guard who would unplug a refrigerator-full of frozen food to power his boom box. He wouldn't repower the refrigerator when he left at shift end. {That really happened #2.}

[This message has been edited by Bjarney (edited 10-30-2002).]

#103693 - 10/31/02 11:43 AM Re: ECN Violations Photo Forum  
Hazmat  Offline
Joined: Mar 2002
Posts: 30

I've got to add to your example of the server. In our Texas plant, the network administrator came in several days in a row, to find his Desktop, as well as the network server had been powered down (unplugged), which really screws things up. He asked everyone on night shift if they were doing it, including janitorial staff. Of course, no one knew what he was talking about.

After 8-10 times of this happening, he bought one of those miniature eyeball cameras, and installed it on his computer. Set to "spy" on the world, he went home on Friday.

Sure enough, Monday, comes back in and same thing. Fires up the 'puter and downloads the stop action shots of the darn janitor, not only unplugging this thing, but the best part was the little "lasso action" move he made as he jerked the cord from 20 feet away.

Hits him up that evening, and he denies it. IT guy then points out that "lasso" shot which was now everyone's screensaver....

Some people's is stupid...

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Joe Tedesco
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