And to get |X+Y+Z| (the line current an ammeter would show on A), you just take the square root of the sum of the squares of the two components of X+Y+Z.
I was using vector notation (a,b) where a and b are the two components. So a = |X| + sqrt(3)/2 (|Y|+|Z|) is the component of X+Y+Z in phase with L-N, and b = (|Y| - |Z|) / 2 is the component of X+Y+Z 90 degrees out of phase with L-N.
Then if you calculate sqrt(a2+b2) that's the magnitude of the line current. A little too lengthy for me to write out here in terms of X, Y, and Z.
