robiner@ganelon.usc.edu (Steve) (07/16/88)
I'm sure this is below the level of most of the people in this group, but... Why do standard electrical plugs have holes in the metal prongs? =Steve=
kinsell@hpfclm.HP.COM (Dave Kinsell) (07/18/88)
>I'm sure this is below the level of most of the people in this group, >but... > >Why do standard electrical plugs have holes in the metal prongs? Those are drain holes for the mercury.
howard@tp2.Waterloo.NCR.COM (Howard F. Steel) (07/18/88)
In article <10790@oberon.USC.EDU>, robiner@ganelon.usc.edu (Steve) writes: > > Why do standard electrical plugs have holes in the metal prongs? The holes serve (or served) as detents for the mating ends. A small knob on the mating surface of the outlet notched into the hole to make accidental removal less likely (especially after the socket has aged and worn a bit). -- Howard FP Steel :-( I Think, Therefore, I Am aka: "The Duck" :-) I Think
robert@richp1.UUCP (Robert Miller) (07/19/88)
In article <10790@oberon.USC.EDU> robiner@ganelon.usc.edu (Steve) writes:
[I'm sure this is below the level of most of the people in this group,
[but...
[
[Why do standard electrical plugs have holes in the metal prongs?
[
[=Steve=
That's a good question! Along the same line, why is the ground prong
round instead of flat like the other two?
Just wondering.
--
.......................................
"To open, cut along dotted line." ....:.......................................
: : Robert Miller @ ihnp4!richp1!robert
.....hermann@calgary.UUCP (Michael Hermann) (07/19/88)
In article <10790@oberon.USC.EDU>, robiner@ganelon.usc.edu (Steve) writes: > I'm sure this is below the level of most of the people in this group, > but... > > Why do standard electrical plugs have holes in the metal prongs? > > =Steve= Lots of industrial type units for three-phase power etc. have a locking mechanism that either involves rotating the plug, or using a latch that locks some internal pins into the plug thru the holes. Safety feature, prevents accidental disconnection (ie. seen these outlets in hospitals, where heart monitors etc. are plugged in). -- /------------------\ ARPA calgary!hermann@cs.ubc.ca | Mike Hermann | UUCP ...uunet!alberta!calgary!hermann \------------------/ EAN hermann@cpsc.calgary.cdn God is Real!!! (unless declared an integer)
henry@utzoo.uucp (Henry Spencer) (07/19/88)
In article <10790@oberon.USC.EDU> robiner@ganelon.usc.edu (Steve) writes: >Why do standard electrical plugs have holes in the metal prongs? The holes, and corresponding spring-loaded bumps in outlets, were/are an extra bit of insurance against the plug coming out unintentionally. This was of considerable importance early on, when making alloys that stayed springy over many years was quite a trick. It's less important now. -- Anyone who buys Wisconsin cheese is| Henry Spencer at U of Toronto Zoology a traitor to mankind. --Pournelle |uunet!mnetor!utzoo! henry @zoo.toronto.edu
rfarris@btree.uucp (rick farris) (07/19/88)
:[Why do standard electrical plugs have holes in the metal prongs? : :That's a good question! Along the same line, why is the ground prong :round instead of flat like the other two? : Yes, and why the heck are manholes round?
palmer@tybalt.caltech.edu (David Palmer) (07/19/88)
In article <303@btree.uucp> rfarris@btree.UCSD.EDU (rick farris) writes: >:[Why do standard electrical plugs have holes in the metal prongs? Argument from authority: Cecil Adams (as reported in "_More straight Dope_") asked various people in the industry. It turns out that early sockets could not hold plugs firmly enough, and so the holes were to give the sockets something to grip on. >:That's a good question! Along the same line, why is the ground prong >:round instead of flat like the other two? To fit the round hole in the socket of course. There are no stupid questions, but if there were, that would be one of them. :-) >Yes, and why the heck are manholes round? So that the manhole cover cannot fall into the hole, as it could if they were square. David Palmer palmer@tybalt.caltech.edu ...rutgers!cit-vax!tybalt.caltech.edu!palmer "Flowers -- Just say NO!!" - Mighty Mouse
anand@vax1.acs.udel.EDU (Anand Iyengar) (07/20/88)
In article <303@btree.uucp> rfarris@btree.UCSD.EDU (rick farris) writes: >Yes, and why the heck are manholes round? So that they can't fall into man-holes. Think about it: putting a disk through a (non-deformable) circular openning of smaller diameter... Square cover's, on the other hand, can be turned vertical and rotated 45 degrees and dropped into the corresponding openning (rectangles, similarly). Anand.
jackg@tekirl.TEK.COM (Jack Gjovaag) (07/20/88)
In article <303@btree.uucp> rfarris@btree.UCSD.EDU (rick farris) writes: >:[Why do standard electrical plugs have holes in the metal prongs? >: >:That's a good question! Along the same line, why is the ground prong >:round instead of flat like the other two? >: > >Yes, and why the heck are manholes round? Aha! I know the answer to this one, even though it has nothing to do with electronics. Round is the only shape for the cover that guarantees that the cover can't fall into the hole. What do I win? -- Jack Gjovaag Tek Labs
lkraft@hpccc.HP.COM (Lyle Kraft) (07/20/88)
Another possibility for the holes is to prevent a piece
of equipment from being plugged in. That is, a defective
piece of equipment that has been identified as a safety
hazard but has not yet been repaired. A small padlock may
be slipped through one or both holes to prevent insertion
into an outlet.
My $0.02 worth.tomk@lakesys.UUCP (Tom Kopp) (07/20/88)
In article <303@btree.uucp>, rfarris@btree.uucp (rick farris) writes: > > Yes, and why the heck are manholes round? Correct me if I'm wrong, but I believe the reason manholes are round is because it is impossible for a manhole cover to be pushed through the manhole, even though the actual hole is only minimally 'smaller' due to the rim than the cover. No matter how you turn it, a circle still has the same radius. Picture a square manhole, if you will. Each side being 2 feet in length (just for the purpose of this discussion). each side of the manhole is the same length, as is (of course) and measurment taken parallel to any side. However, between opposite corners, A and C below: A-----B | | | | D-----C The distance is the square root of 8 by pythagorean theorem (sum of the squares of A-D and D-C equals the square of A-C) which is >2. Thus, if you were to first rotate it on the A-D axis so that it were perpendicular to the ground, With B-C as the top and A-D as the bottom, then rotated it upon the A-B axis 45 degrees counter-clockwise (as seen from above) You could drop the cover straight through, as you would be putting an object of length 2ft through an opening of length (sqrt(8))....They don't want people dropping covers through the holes as they're quite heavy. This has been rather verbose, but I don't care. So sue me. -- _____ _____ |"Reading computer manuals without |tomk@lakesys.UUCP | | | the hardware is as frustrating as |uunet!marque!lakesys!tomk | \_| | reading sex manuals without the |uunet!uwmcsd1!lakesys!tomk ------------- software" - Arthur C. Clarke ----------------------------
ltf@killer.DALLAS.TX.US (Lance Franklin) (07/20/88)
In article <1550@tekirl.TEK.COM> jackg@tekirl.TEK.COM (Jack Gjovaag) writes: >In article <303@btree.uucp> rfarris@btree.UCSD.EDU (rick farris) writes: >>Yes, and why the heck are manholes round? > >Aha! I know the answer to this one, even though it has nothing to >do with electronics. Round is the only shape for the cover that >guarantees that the cover can't fall into the hole. What do I win? A great big no-prize...a equilateral triangle for a manhole cover wouldn't fall into the hole either. And think of the other uses...paint them orange and point them in the direction of one-way streets. And they wouldn't roll away when you pull em off, either. Lance -- +------------------+ +------------------------------------------------------+ | Lance T Franklin | | Now accepting suggestions for clever, humourous or | | ltf@killer | | incredibly insightful .signature quote. Send Now! | +------------------+ +------------------------------------------------------+
richr@ai.etl.army.mil (Richard Rosenthal) (07/20/88)
Re: Man Hole Covers Triangular (3 sided) covers cannot fall through the hole. Nashua, New Hampshire has such covers. They are placed in the street such that one of the points of the cover points down hill. Maintenance crews at the surface always know which way the system flows. -- Richard Rosenthal Internet: richr@ai.etl.army.mil Engineer Topographic Labs UUCP: ...!ames!ai.etl.army.mil!richr Ft. Belvoir, VA 22060-5546 BITNET: richr%ai.etl.army.mil@CUNYVM +1 202 355 2830 CSNET: richr%ai.etl.army.mil@RELAY.CS.NET
jps@wucs2.UUCP (James Sterbenz) (07/20/88)
In article <1550@tekirl.TEK.COM> jackg@tekirl.TEK.COM (Jack Gjovaag) writes: >In article <303@btree.uucp> rfarris@btree.UCSD.EDU (rick farris) writes: >>Yes, and why the heck are manholes round? >Round is the only shape for the cover that guarantees that the cover can't >fall into the hole. What do I win? Nothing. I suspect that any regular polygon with an ODD number of sides couldn't fall into the hole. Think about trying to rotate a triangle or pentagon to fit! A circular cover is just easier to manufacture (kinda like a polygon with an infinite number of sides :-). -- James Sterbenz Computer and Communications Research Center Washington University in St. Louis 314-726-4203 INTERNET: jps@wucs1.wustl.edu UUCP: wucs1!jps@uunet.uu.net
wrv@ihlpm.ATT.COM (Vogel) (07/20/88)
In article <303@btree.uucp> rfarris@btree.UCSD.EDU (rick farris) writes: >:[Why do standard electrical plugs have holes in the metal prongs? >: >:That's a good question! Along the same line, why is the ground prong >:round instead of flat like the other two? >: > >Yes, and why the heck are manholes round? This is serious! A friend of mine was asked that exact question on a job interview right after graduating. He replied: "well, have you ever seen a typical sewer worker? He wouldn't fit if they weren't round". He got the job! (EE at some big company). -Bill Vogel
heppell@cory.Berkeley.EDU (Kevin G. Heppell) (07/21/88)
In article <4862@killer.DALLAS.TX.US> ltf@killer.DALLAS.TX.US (Lance Franklin) writes: > ...a equilateral triangle for a manhole cover wouldn't >fall into the hole either. >-- >+------------------+ +------------------------------------------------------+ >| Lance T Franklin | | Now accepting suggestions for clever, humourous or | >| ltf@killer | | incredibly insightful .signature quote. Send Now! | >+------------------+ +------------------------------------------------------+ I don't know about you, but I _can_ get a triangular cover down the hole. Think about it: a line which divides the cover into two right triangles is only sqrt(3)/2 as long as a side - just hold one edge vertical and drop the cover along one side of the hole. Round covers also have the advantage of minimizing stress concentration (i.e. they distribute loads well) when something drives over. ------------------------------------------------------------------------------- Kevin G. Heppell 784 Santa Barbara Rd. USENET: ucbvax!cory!heppell Berkeley, CA 94707-2046 arpa: heppell@cory.Berkeley.EDU (415) 528-6396
ltf@killer.DALLAS.TX.US (Lance Franklin) (07/21/88)
In article <4566@pasteur.Berkeley.Edu> heppell@cory.Berkeley.EDU.UUCP (Kevin G. Heppell) writes: >In article <4862@killer.DALLAS.TX.US> ltf@killer.DALLAS.TX.US (Lance Franklin) writes: >> ...a equilateral triangle for a manhole cover wouldn't >>fall into the hole either. > > I don't know about you, but I _can_ get a triangular cover down the hole. > Think about it: a line which divides the cover into two right triangles > is only sqrt(3)/2 as long as a side - just hold one edge vertical and > drop the cover along one side of the hole. Whoops...... (facesaving mode on) Of course, I meant a four-sided polyhedron with equilateral trangles for faces. Didn't I? (-: Lance :-) -- +------------------+ +------------------------------------------------------+ | Lance T Franklin | | Now accepting suggestions for clever, humourous or | | ltf@killer | | incredibly insightful .signature quote. Send Now! | +------------------+ +------------------------------------------------------+
keithe@tekgvs.GVS.TEK.COM (Keith Ericson) (07/23/88)
>In article <303@btree.uucp> rfarris@btree.UCSD.EDU (rick farris) writes: >:[Why do standard electrical plugs have holes in the metal prongs? My dad always put a little padlock in them to keep me from using his power tools. I guess one burned-out drill motor was enough... keith
thearlin@vdsvax.steinmetz.ge.com (Kurt Thearling) (07/28/88)
In article <134@ai.etl.army.mil> richr@ai.etl.army.mil (Richard Rosenthal) writes: >Re: Man Hole Covers > >Triangular (3 sided) covers cannot fall through the hole. > this is incorrect. using the following figure, it is easy to see that the length AC is shorter than the length AB. thus, if the manhole were held such that AC were parallel to the ground, the manhole could be dropped through the hole along AB. A /|\ / | \ / | \ Note: not drawn to scale. all sides are / | \ assumed to be the same length (i.e., / | \ AB = AC = BD). also assume that / | \ BC = CD. ------------- B C D kurt ----------------------------------------------------------------------- Kurt Thearling thearlin%vdsvax.tcpip@ge-crd.arpa General Electric CRD thearlin@vdsvax.steinmetz.ge.com Bldg. KW, Room C313 uunet!steinmetz!vdsvax!thearlin P.O. Box 8 thearlin%vdsvax@steinmetx.uucp Schenectady, NY 12301 kurt%bach@uxc.cso.uiuc.edu (518) 387-6779 kurt@bach.csg.uiuc.edu -----------------------------------------------------------------------