Conductor Cross Sectional Area

The strands do not occupy the full area; there are spaces between them.

You need to use the area of each strand, multiplied by the number of strands.

This is a very think cable. So two additional ideas come to my mind besides the voids between the strands. First, you might be confusing conductor diameter with cable (conductor and insulation) diameter. Second, a conductor this thick will have the skin effect reduce the effective cross sectional conduction area reduce. At 60 Hz a copper conductor has a skin effect depth of only 8.5mm.

I heard skin effects are important just in UHF frequency course is not easy verify if you need wires bigger than 17mm after you if i understood and i guess not..-

As tornado and redfer indicated correctly you have the following:

1.- The area of the cable is the area of each conductor, and since they are round they will not contact evenly so you would have to calculate the space in between as part of the total area.

2.- To this you have to add the additional area due to shielding, bonding elements, sheats, etc., so you overall cross section will always be bigger than the calculated one.

Furthermore you need to check with individual manufacturers since the way they twist the cables will also affect the overall area.