The mid span clearance calculation is taken from AS/NZS 7000 2016 3.7.3.2. The k constant defaults to 0.4. The conductor sag is taken at 50°C in still air.

The voltage of a cable is taken to be the voltage of the circuit. If the cables being compared are on different circuits the phase difference is assumed to be 180°. If the cables being compared are on the same circuit and the circuit has 3 or 4 cables then the phase difference is taken to be 120°. If the cables being compared are on the same circuit and the circuit has only two cables, one of the cables is assumed to be live and the other neutral.

This calculation is performed between all pairs of conductor running between the same two poles.

The projection line for calculating the projected horizontal distance between the conductors is taken to be the the line created by connecting the point in the middle of the conductors at one end of the span to the point in the middle of the conductors at the other end of the span. The following two diagrams shows two examples of this calculation.

In the above top view diagram where AB and CD are conductors the projected horizontal distances at either ends of the conductors are AC and BD. The projected horizontal distance at the midspan then becomes (AC + BD) / 2.

In the above top view diagram AB and CD are conductors. E is the midpoint of AC and F is the midpoint of BD. Line EF is taken as the projection line. A’, B’, C’ and D’ are the closest points on the projection line to A, B, C and D respectively. (AA’ + CC’) and (BB’ + DD’) are taken as the projected horizontal distances at either ends of the conductors. The projected horizontal distance at the midspan then becomes (((AA’ + CC’) + (BB’ + DD’)) / 2).

The clearance calculation is taken from AS/NZS 7000 2016 3.7.3.3. The q constant defaults to 0.005. The phase difference between the conductors is assumed to be 180°. This calculation is performed between all pairs of conductor on different circuits running between two poles.