This is all wrong. In Germany, and maybe in other countries too, 3 phase power is brought into the home, as a 5 wire system. There are the 3 "hots" at 400 V between them, 1 neutral, and 1 safety ground. Single phase voltage is derived by going from one of the hots to the neutral. The nominal voltage is 230 V. The connections are usually wye or star.
Three phase is used for heaters and large appliances. Single phase for everything else. In the US, the 3 phases on the pole are at 13.5 kV line to line. In older systems, transformers were connected delta across two phases and produced an output at the secondary of 240 V single phase. The transformer is tapped to produce 120 V service by connecting any end to the centre. The centre is usually grounded (earthed). Newer systems connect in wye with the centre of the transformer winding of the primary at 13.5 kV and the outer part of the winding closest to the can being at ground potential. This is safer then the delta type as it reduces the chance of the can being live at 13.5 kV. The secondary output is the same. The international method is not used in the US except in some instances where three phases of 207 V line to line are used for lighting. The single phase voltage line to neutral is 120 V. Mexico uses this system but has a 220 V line to line system with 127 V line to neutral. ----- Original Message ----- From: "Carleton MacDonald" <[EMAIL PROTECTED]> To: "U.S. Metric Association" <[EMAIL PROTECTED]> Sent: Wednesday, 2004-02-04 20:38 Subject: [USMA:28533] Re: Torque and horsepower > I think that this is what is done. The power company probably divides the > wires on the low-voltage side of the transformer to even the load; that is, > about a third of the houses get 220 v from phases 1 and 3, a third from 2 > and 3, and a third from 1 and 2. > > cm > > -----Original Message----- > From: Nat Hager III [mailto:[EMAIL PROTECTED] > Sent: Wednesday, February 04, 2004 20:00 > To: [EMAIL PROTECTED]; 'U.S. Metric Association' > Subject: RE: [USMA:28531] Re: Torque and horsepower > > Carleton, > > Two phases would differ by 180� whereas 3 would differ by 120�. So > could you really just take 2 of the 3 phases for home use, and get the > same thing? > > Nat > > >>>Normally two of the three phase wires come into a home. Across the > two, it's 220 v (nominally) and is used for high-amperage appliances > such as stoves, ovens, water heaters, air conditioners, and dryers. > >From either to neutral is 110 v (again nominally) for lighting and other > general purpose uses > >> > >
