FYI... ---------- From: "Wong, Ed" <[EMAIL PROTECTED]> Date: Wed, 11 Apr 2001 09:51:07 -0400 To: "'Ed Heckman'" <[EMAIL PROTECTED]> Subject: Plugs, humans and grounds.... I cant post to the MD list from this address - feel free to repost.... > why some plugs are polarized (one prong is wider than the other) > So we're all kinda sleeping though EE2 or was that EE3... except for the really nerdy types who are paying rapt attention. We're doing AC - and the math gets really weird. The guy who teaches the class is some big power engineer for PSE&G (the big central NJ power supplier) Turns out since few people like doing this stuff - you can make alot of $$$ at it if you are good at it (aka you *like* it). Near the end of class, some guy raises his hand in the back (Id like to say it was me, but it wasnt) and asks... We all now know that AC means that the voltage fluctuates between + and - an approximate 115 volts (in a standard single phase North America standard AC outlet). Thanks to todays lecture we now are armed with the ability to calculate the phase angle differnces between the three phase poles. So why do AC powered itmes have these polarized plugs? It makes no difference to the "motor" which way the plug goes it. If it goes in the wrong way - the motor is just phase shifted - not "inverted" or "reversed". Obviously inductive devices (aka heaters etc) could care less about phase or polarity. The response was intersting... In turns out that some items are "case" grounded. Thus the shell has some voltage at its surface. The voltage is not enuff to pierce the skin - (calculated in a seperate lecture in Electromagnetic Field ), so you dont get a shock. But if you were to pick up two devices and the case grounding were to be out of phase (aka the plugs reversed) then the potential differnce between the two hands would be.... (rapid scribbling from the guys up front - and a shout of 2 times 120v is 240v from the middle of the room) For a bonus question - what is the estimated power range of the tools in question in order to electrocute the home handyman in the above scenario? *Define* all appropriate assumptions taken... ----------------------------------------------------------------- To stop getting this list send a message containing just the word "unsubscribe" to [EMAIL PROTECTED]
