why are there holes in electric plug prongs?

[*alan*]

Not technically a home repair topic, but:

Do the holes in the prongs of an electric plug serve any purpose? If so, what is that purpose? Thanks for any information.

-- alan (just curious)

[JoeSpareBedroom]

Why is there never a plug historian around when we need one?

[*alan*]

I'm confident that one will come to the rescue ;-)

[jim]

[Tony Hwang]

Hi, When you plug it in it mates with dimpled tab to make secure contacts. If in double break apart a receptacle(only couple dollars a piece) and see for yourself.

[*alan*]

Jim!

[*alan*]

Thanks Tony!

[news]

come on now, lets tell alan the truth...it's so you can snip off the grounding plug, and then its easier to snip through the blade, cause it's usually the larger one, then you can plug it into a 2 prong nongrounded plug........ your welcome

[Richard J Kinch]

Also if the device being powered is shorted, when you insert the plug into an outlet, the narrower conductor around the hole tends to melt off (pow!) before you can insert the plug all the way. I don't know that this is by design, but it is a beneficial aspect.

[salty]

I have also seen them used as a "lock out" by use of the same type of seal as used on electric meters being passed through them so it can't be plugged in.

[DT]

The Straight Dope addressed this question, and there seems to be no one simple answer:

Just for the record, I just dismantled two outlets, one inexpensive one and the other a high end commercial quality Decora... no dimpled tab in either, just flat copper strips.

[Jeff Wisnia]

I always figgered those holes were there so that in a pinch you could make an erzatz extension cord out of a length of 14 gage Romex.

The holes in the plug blades makes it easier to crimp the stripped solid wires onto them, and then you just make narrow U-bends in the stripped other ends, pound them flat, and jam them into the two slots of a receptical.

Jeff (Never believe everything I say )

[Mark Lloyd]

I have one extension cord that uses those holes to lock the plug in place.

[mm]

They are there to help the roaches rappel down to lower floors.

[mm]

I think it's because putting holes in things make them stronger, like the guy said. Look at the George Washington Bridge in NYC. It has loads of holes and look at how strong it is.

I have a related question. Why are some prongs solid, others are folded over with each layer totally flat against the other, and still others are foled over but have one side freely attached and springy.

The third kinds seems the best.

But sometimes with the second type, I force the two layers apart so the plug will stay in the outlet better.

Why don't they make this easier to do?

Will I cut my finger off?

[Oren]

Those are called Wonders. Ever wonder what they were for?

Like scratching your ass, if your finger don't stink, it's a wonder!

[Kurt Ullman]

I can tell you this has been around a lot longer than the 20 years Cecil discussed. I have an old, big, tube radio for the 40s with the original equipment plug and it has the holes.

[Jimmie D]

I asked a retired engineer that worked for GE this question a long time ago. I was 18 and he was about 65 at the time. His answer was a little different from the howstuffwprks answer. He gave the same discription of the socket but said it improved the electrical connection instead of holding the plug in the socket better. It allowed the bump to contact the plug over a larger area. After thinking about it the design probably does both. Just think a bump touching a flat blade or a bump fiting down in a hole. which is going to have the largest area of contact.

Jimmie

[Chris Lewis]

The straight dope piece seems to have gotten it right - about it _used_ to be necessary with old outlets that didn't grip so well, the pins could interlock into buttons on the tabs. So, it used to have a reason, and now it's probably they can't figure out why they're there, so it's easier to stay that way ;-)

Nope.

Punching holes in metal structures does not make them stronger. In fact, it makes them somewhat weaker than equivalently sized solid structures. The reason punching holes (or leaving it out altogether such as in trusses) it is to make it _lighter_.

They're aiming for the rigidity implied by the larger cross-section, without some of the added weight.

The only ones of the third kind I've seen have been folded types that wore so badly that the join (at the tip) is gone. Or were clipped. The temptation for one to go sideways is too high.

As to why some are folded and some are solid - different manufacturing processes.