firstname.lastname@example.org wrote: [snip]
The only motor-generator sets in use when I joined the phone company in the 1970's were used for creating 90v, 20Hz ringing voltage and +/-110 volt coin collect/return battery. All the MG sets ran off the -48V CO battery plant, which was floated across the -48 rectifier outputs powered from commercial mains. These MG sets were replaced with solid-state units in the 1980's, although I think the MG sets were kept as standby units well into the 90's.
Some CO's also had independent alternators in case of power failure: many of them powered by jet engines, and so powerful that they were actually used to generate power for the electric grid during summer brownouts.
I don't know why, but Europe uses 50 Hz AC power, instead of the 60Hz we favor in the US and Canada.
Despite the different frequency, both US/Canadian and European homes have single-phase power; nobody bothers with three phase for homes, because there isn't enough demand in homes to justify the added expense of installing three-phase power.
The difference is that European homes receive a 220-volt, single-phase feed at their electric outlets, which is, of course, twice the "110" volt standard used on this side of the Atlantic. The higher voltage means lower current for the same wattage, thus allowing smaller wire sizes and concomitant savings in home construction costs.
William Warren (Filter noise from my address for direct replies)