Re: Two phase systems
I am certainly not an old electrician, but I do have some knowledge of these systems. They are indeed vintage and rarely seen. There is actually 3-wire, 4-wire, and 5-wire Two Phase system arrangements. The 3-wire system operates at 120-volts between each phase and the common and 170-volts between phases. This is because current at the common will be 1.414 times the nominal system. This is the square root of two. 4-wire systems do not have a common, but two wires with a 120-volt potential between them for each of the two phases. 5-wire is the most complicated, but is basically a center tap common of four phase conductors. Many line voltages can be created, mainly being 120-volt to ground, and 155-volt between phases.
