>From the point of view of an electrician or a technician, I can understand, to some extent, how one could consider a phase-to-phase connection as being single phase. From the point of view of a design engineer, however, there would probably be some differences. With a system that references neutral you might only use one circuit breaker for instance and one of the wires connected to the power supply would be blue.
There is also a potential problem in providing documentation for customers. If a vendor's documentation specifies a single-phase connection and indicates that the power supply is auto-ranging, a European customer would assume that the product was plug and play compatible with European line voltage. When he plugged it in, however, the supply would fry with 400V, phase-to-phase voltage across the inputs. You could solve this problem, I suppose, by sending the European customer a "true" single-phase system and sending the American customer a "pseudo?" single-phase system. For U.S. customers, you need to add a voltage specification to try to help the him understand the requirements since some customers might expect that the term single phase means a phase to neutral connection. Many (most?) manufacturer's might say "220 VAC, single-phase" to clarify things. Now the plot thickens even more since there is no such thing as "220 VAC" in the U.S., unless the customer has some unusual facilities wiring. Standard, nominal voltages in the US for light-industrial installations are 208 and 120. At this point, I wouldn't be surprised if the vendor were to get a call from a customer asking: "Hey do you guys really know what you're doing?". Another potential problem I see with calling both a phase-to-phase connection and a phase-to-neutral connection, "single-phase" is that it presumes that all power supplies can be connected either way. What if a vendor designs a system in which the power supply is changed many times over the years? Can you be absolutely, 100% sure that any power supply that you, or your successor, select will work with a phase-to-phase connection? Would you bet your reputation on it? Would you bet your job on it? What if the guy that designed the power supply happened to hang a relatively low-voltage capacitor from the neutral input to ground, for instance? It's possible, I suppose, that a technician or electrician might be able to use the same term to describe two different configurations. A design engineer cannot. Max Kelson Evans & Sutherland -----Original Message----- From: Doug McKean [mailto:dmck...@corp.auspex.com] Sent: Thursday, May 03, 2001 7:30 PM To: emc-p...@majordomo.ieee.org Subject: Re: AC Power Primer? In my experience, a system that gets its power from a power supply which for input has either a transformer or a switcher with a two port input across which is connected one hot line and one neutral line or two hots out of phase from each other, that system is a 'single phase' system. Even though two phases may be used as power input, the effectivity is to act as a single phase input and can operate that way as well. In other words, if you can plug and chug with no problems by replacing an input consisting of two hots out of phase from each other by a single phase hot/neutral input, then you've got a single phase system. It's effectively what the primary 'sees', one phase and that's what's counts, AFAIC. Regards, Doug McKean ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson: pstc_ad...@garretson.org Dave Heald davehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://www.rcic.com/ click on "Virtual Conference Hall," ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson: pstc_ad...@garretson.org Dave Heald davehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://www.rcic.com/ click on "Virtual Conference Hall,"
