>-----Original Message----- >From: mkel...@es.com [mailto:mkel...@es.com] >Sent: Thursday, May 03, 2001 8:22 AM >To: brian.harl...@vgscientific.com; emc-p...@ieee.org >Subject: RE: AC Power Primer? > > > >Just out of curiosity, where does the designation "220V come >from? If you >measure the potential difference between two phases of a >three-phase system, >you get 208V. If you measure the difference between the two >phases in a >residential or light commercial area, you would probably get 240V. > >So, where does the term "220V" come from? > >Thanks, > >Max Kelson >Evans & Sutherland >
[SNIP] Max: There's many more expert than I on this subject, but.... The USA has several "standard" powers available to non-heavy industrial consumers. A typical home is supplied with a three-wire drop (although the trend is not to drop, but to bury the feeders) that consists of two hot wires and a return. The return line is grounded. The voltage from hot to hot is 240 Vrms, and is a single phase. The transformer that supplies the several homes on the last power branch has a center-tapped secondary, so the voltage from either hot to the center-tap is 120 Vrms. I have heard the hot-to-center-tap voltage called 110 V, 115 V, 117 V and 120 V. That would mean the hot-to-hot voltage would be either 220 V, 230 V 234 V or 240 V. FWIW, the voltage at my home (between blackouts, I live in Southern California) consistently runs about 119 Vrms. High-power appliances (air conditioning, range, heating) are usually designed to draw from the hot-to-hot 240 Vrms (this minimizes losses). Lesser loads are connected from one hot to the neutral, hopefully with some thought toward balancing the total load. Light industrial users are often fed by a five-wire three-phase wye system (three phases, neutral and safety ground). The nominal 208 Vrms value exists from any phase-to-phase pair. The voltage from any phase to neutral is 115 Vrms. Heavy loads (large motors) are usually 3-phase models, and other heavy loads (like industrial ovens) also draw phase-to-phase power. The phase-to-neutral voltage is close enough to residential values that ordinary lights, appliances and computers can be fed from this circuit. Again, you should try to balance the phase-to-neutral loads. Regards, Ed Ed Price ed.pr...@cubic.com Electromagnetic Compatibility Lab Cubic Defense Systems San Diego, CA USA 858-505-2780 (Voice) 858-505-1583 (Fax) Military & Avionics EMC Services Is Our Specialty Shake-Bake-Shock - Metrology - Reliability Analysis ------------------------------------------- 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,"
