Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!rutgers!cs.utexas.edu!uunet!ncrlnk!ncrwat!swdev!tp2!howard
From: howard@tp2.Waterloo.NCR.COM (Howard F. Steel)
Newsgroups: sci.electronics
Subject: Re: Polarized Plugs
Summary: Polarized means Polarized
Message-ID: <414@tp2.Waterloo.NCR.COM>
Date: 9 Jun 89 12:29:50 GMT
References: <5558@clint.megatest.UUCP>
Reply-To: howard@tp2.UUCP (Howard F. Steel)
Distribution: usa
Organization: NCR Canada Ltd., Waterloo, Ontario, Canada
Lines: 30

In article <5558@clint.megatest.UUCP> jao@megatest.UUCP (John Oswalt) writes:
>What is the point of 2-pronged polarized electrical plugs?  (The kind
>where one prong is wider than the other.)  It seems to me that the only
>difference in "signal" between the two prongs is a 1/120 second phase
>shift.

1 pin of the plug is connected to (in North America) the live side of the line
(120/117V); the other pin is connected to the earthing (grounding) conductor
of the mains transformer. This makes the one pin effectively 0 volts; the small
voltage measured on that pin (to ground) is a result of the line resistance
back to the actual ground.

>It is a rare gadget indeed to which this matters.

True, in the event that everthing is running normally, but if an insulation
fault were to occur and the plug was reversed, the chassis or other dead metal
parts of the unit could become live, presenting the owner/operator with a
potentially life threatening situation should they come into contact with a
real ground.

Most things which employ the 2 pin method rather than three prong are either
double insulated to reduce the liklihood of such a fault or the metal parts
are kept isolated from the AC line.

Net result is not too much apparent difference, but a lot of (excuse the pun)
potential difference.

-- 
Howard.Steel@Waterloo.NCR.COM  :-(  	I Think, Therefore I AM,
aka: Howard "The Duck" Steel   :-) 		I think