For simplicity (and because I'm almost late for work), draw an equilateral triangle (all sides the same length). Label each side
240-that's the voltage between any two corners of the triangle. Notice the "delta" shape of your drawingNow, drop a line from the top corner down perpendicular to the base. That divided the base into 2 equal parts, both 120 volts "long" from the center of the base
The top corner is the "wild leg". Using basic trig (Pythagorean theorem), the length of the line you dropped is the square root of (240X240-120X120), or 208 volts..
Besides delta, there is a "wye" which when drawn, resembles the letter "Y"
Sorry , out of time!!!!!!!!!