Edison himself designed the US residential power system. As inventor of the light bulb he experimented with his carbon filament technology and determined that an optimal filament required ~110V. Recognizing that distance was an issue for his DC generating stations, he designed a system that used 220V with a center tap. Inside a residence loads are placed approximately half on each side of the supply. The center tap only has to carry the difference current to assure a steady 110 V on each side of the split. This allowed it to be relatively light gauge which saved on copper expense. Heavy appliances simply bridge across the full 220V supply. So there you have it: the distance advantage of 220V applied to 110V lamps. Long ago a nation wide survey of household voltages was taken, and the average was 117V. This became the US domestic standard, since rounded up to 120/240V.
On a side note, incandescent lamps last much longer on DC. With AC you have the slight but constant of temperature cycling on each half cycle of current, plus the slight but constant mechanical flexing by alternating magnetic interaction with the earth's own field. It can make a difference whether the filament is north-south or east-west! Orin Laney On Mon, 20 Jul 2009 19:06:34 +0100 John Woodgate <[email protected]> writes: > In message > <[email protected]>, > dated > Mon, 20 Jul 2009, Ralph McDiarmid <[email protected]> > writes: > > >Is it common throughout Europe to distribute 3-phase power to > >single-family homes? > > Not in UK. Elsewhere, yes, but I don't know about some countries, > such > as Portugal and Greece. > > > If so, why are single-family and duplex residences in North > America > >supplied with 120/240V single-phase? > > Well, there is an interminable argument over whether that's single > phase > or two phase, not that it matters. > > It seems that there are historical reasons. US decided to go for a > low > voltage, high current principle, while Europe went the other way, > with a > factor of 2. Maybe the difference in prices of copper in 1910 (?) > was a > factor? Or the Edison/Tesla controversy? > > Consistent with that, US distribution technique is to carry MV close > to > customers and feed only a few, at high current, from one MV/LV > transformer. In Europe, MV/LV transformers are typically 500 MW and > feed > hundreds of customers. > -- > OOO - Own Opinions Only. Try www.jmwa.demon.co.uk and > www.isce.org.uk > Things can always get better. But that's not the only option. > John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK > > - > ---------------------------------------------------------------- > This message is from the IEEE Product Safety Engineering Society > emc-pstc discussion list. To post a message to the list, send your > e-mail to <[email protected]> > > All emc-pstc postings are archived and searchable on the web at: > http://www.ieeecommunities.org/emc-pstc > Graphics (in well-used formats), large files, etc. can be posted to > that URL. > > Website: http://www.ieee-pses.org/ > 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]> > - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <[email protected]> All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc Graphics (in well-used formats), large files, etc. can be posted to that URL. Website: http://www.ieee-pses.org/ 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]>
