Yes, I find it interesting in this age of better safety standards (creepage & clearance requirements, double insulated appliances, production hipot, etc.) the plug standard in the U.S. is now polarized. Polarized plugs were needed 40-50 years ago, when we had 'hot chassis' appliances, not now.
Pat Lawler EMC Engineer SL Power Electronics Corp. [email protected] [email protected] wrote on 08/10/2006 06:04:27 AM: > I recently bought a little Radio Shack wallwart power supply, > equipped with two parallel-blade AC power terminals (with no ground > blade) and a 6 VDC output wire pair. As you would expect, one of > the blades is slightly wider than the other (implying that this is > the neutral or return line), conforming to the convention of the > typical NEMA 15 Amp female power receptacle. Since the AC power > blades are located near one edge of the wallwart, you can plug the > wallwart into a receptacle and the bulk of the wallwart body hangs > to one side of the receptacle. > > Unfortunately, when you try to plug in a second wallwart, the bulk > of the wallwart body prevents you from plugging it in, and the > larger AC power blade prevents you from facing this second wallwart > opposite the first one. > > My question is, why does this appliance have a polarized blade > power connector? I am assuming that the input power pins go > directly to the primary of a transformer, so why should we worry > about which side is "high" or "return"? Could wallwarts be designed > using identical power blades, allowing the option of a 180-degree > rotation installation? > > Ed Price > [email protected] WB6WSN > NARTE Certified EMC Engineer & Technician > Electromagnetic Compatibility Lab > Cubic Defense Applications > San Diego, CAUSA > 858-505-2780 (Voice) > 858-505-1583 (Fax) > Military & Avionics EMC Is Our Specialty > > - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. Website: http://www.ieee-pses.org/ To post a message to the list, send your e-mail to [email protected] Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas [email protected] Mike Cantwell [email protected] For policy questions, send mail to: Jim Bacher: [email protected] David Heald: [email protected] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc ______________________________________________________________________ This email has been scanned by the MessageLabs Email Security System. For more information please visit http://www.messagelabs.com/email ______________________________________________________________________
