120 volt plug blade question

[K8MHZ]

On another forum, a question came up about the small holes in the blades of 120 volt plugs. I found several 'answers' on Google, some of them likely false.

I was just wondering if anyone actually working in the industry knew what the holes are for and if they are required in order to get listed.

Thanks!

 

[kwired]

On another forum, a question came up about the small holes in the blades of 120 volt plugs. I found several 'answers' on Google, some of them likely false.

I was just wondering if anyone actually working in the industry knew what the holes are for and if they are required in order to get listed.

Thanks!

Those are there for makeshift type conditions when you need to power something up and something is broken, missing etc. You simply can take conductors and loop them through those holes and not need a receptacle in a pinch.






I've seen that many times - must be the reason why

 

[user 100]

On another forum, a question came up about the small holes in the blades of 120 volt plugs. I found several 'answers' on Google, some of them likely false.

I was just wondering if anyone actually working in the industry knew what the holes are for and if they are required in order to get listed.

Thanks!

I've heard before that they are for better plug retention- receptacle contacts have bump groove things that the hole slides over when the plug is inserted.

As for them being a necessity for listing, no idea whatsoever.

 

[zbang]

This was discussed multiple times at The Straight Dope-
http://boards.straightdope.com/sdmb/showthread.php?t=622168
http://boards.straightdope.com/sdmb/showthread.php?t=334577
http://www.straightdope.com/columns/read/579/why-are-there-holes-in-the-prongs-of-electrical-plugs

Mostly it seems to come down to "I don't know" or "part of the stamping operation" with a side-order of:
"ANSI/NEMA standard WD 6-2002, which states that the holes are "optional", nonetheless specifies exactly where they should be located and exactly what size they should be -- presumably to rule out alternative designs that might weaken the blade. "

 

[K8MHZ]

I've heard before that they are for better plug retention- receptacle contacts have bump groove things that the hole slides over when the plug is inserted.

As for them being a necessity for listing, no idea whatsoever.

To test the bump theory, I dissected a receptacle and found no bumps, only straight contacts. I hope these pics show that.


View attachment 13987

View attachment 13988

View attachment 13989

View attachment 13990

 

[K8MHZ]

This was discussed multiple times at The Straight Dope-
http://boards.straightdope.com/sdmb/showthread.php?t=622168
http://boards.straightdope.com/sdmb/showthread.php?t=334577
http://www.straightdope.com/columns/read/579/why-are-there-holes-in-the-prongs-of-electrical-plugs

Mostly it seems to come down to "I don't know" or "part of the stamping operation" with a side-order of:
"ANSI/NEMA standard WD 6-2002, which states that the holes are "optional", nonetheless specifies exactly where they should be located and exactly what size they should be -- presumably to rule out alternative designs that might weaken the blade. "

Thanks! The 'straight dope' is on the very last line of the 23 page pdf.

"Hole in flat blade is optional, and intended for manufacturing purposes only. However if used must be located as per dimensions above."

 

[JFletcher]

http://home.howstuffworks.com/two-flat-prong-plug-holes.htm

or wiki:

"The small hole near the end of the power (non-ground) blades of some NEMA plugs is used for convenience in manufacturing; if present, it must be of specified diameter and position.[1] Small specialized padlocks are available to fit these holes, allowing "lockout" of hazardous equipment, by physically preventing insertion of locked plugs into a power receptacle."

https://en.wikipedia.org/wiki/NEMA_connector

 

[user 100]

To test the bump theory, I dissected a receptacle and found no bumps, only straight contacts. I hope these pics show that.


View attachment 13987

View attachment 13988

View attachment 13989

View attachment 13990

I know I have seen the contact bumps before on at least one particular receptacle-IIRC it was an old ivory 2 wire leviton duplex and what stuck out about it is that the brown rear of the device was held on with screws and there were no break off tabs for the side screw terminals-kind of odd. The prong contacts were also more of a flatter "single" contact design rather than the double wipe hook in your photo. Maybe years back those holes were for that?

And an observation- I'm going to assume you dissected a newer 5-15 r and if you did, your photo kind of discredits the declaration that all 15 and 20 amp receptacles have identical guts.

 

[Smart $]

... I was just wondering if anyone actually working in the industry knew what the holes are for ...

My best guess is making the automated machinery pick up and retention better for insertion into connection and/or body molding processes.

 

[K8MHZ]

http://home.howstuffworks.com/two-flat-prong-plug-holes.htm

or wiki:

"The small hole near the end of the power (non-ground) blades of some NEMA plugs is used for convenience in manufacturing; if present, it must be of specified diameter and position.[1] Small specialized padlocks are available to fit these holes, allowing "lockout" of hazardous equipment, by physically preventing insertion of locked plugs into a power receptacle."

https://en.wikipedia.org/wiki/NEMA_connector

I saw that, and Wiki is wrong. I don't know why my pdf link didn't work before, but the following is directly from the NEMA specs for plugs.

"Hole in flat blade is optional, and intended for manufacturing purposes only. However if used must be located as per dimensions above."

Here is a link to the specs from nema.org. Their specs trump anything Wiki has to say. Go all the way to the end of the pdf and look at the very last line.

https://www.nema.org/Standards/Comp...- Dimensions for Wiring Devices - Excerpt.pdf

 

[J.P.]

Those are there for makeshift type conditions when you need to power something up and something is broken, missing etc. You simply can take conductors and loop them through those holes and not need a receptacle in a pinch.






I've seen that many times - must be the reason why

This^

A bit of scotch tape or duct tape and your all set.

 

[kwired]

This^

A bit of scotch tape or duct tape and your all set.

Surprisingly when I see that done they are almost never taped.

 

[badbanano]

I see it as a possible small arc suppressor to keep the flash from projecting outward.

Sent from my XT1080 using Tapatalk