The way I understood it and that made sense when connecting two phases together was that one of the phases was in the exact opposite range(polarity). So one phase would allow current to enter the circuit and then the other phase would allow the current back out of the circuit, back to the source. So it appeared to me that only certain combinations of 2 phases would work. Well, then I read that ANY two phases could be connected together which totally blows that theory up. How come a phase that's only 180' will add up voltage the same as the phase that's a whole 360' in the negative range? I guess any phase to neutral voltage times the square root of 3 will equal the two phases. But why is this true for any phase combination? How does two phases complete a circuit for current to travel? I thought that the 180' would bring in because current is traveling in one direction(positive scale) and then the -180' would take it back as current would then be traveling in the opposite direction(negative scale)?