With reference to norms: IEC 60092 and CEI 11/17 we can affirm as follows:
To determine how tightly a given cable can be bent without damage, the radius of the curve of the inner edge of any bend, shall not be less than 10 times the cable Overall Diametre (O.D.).
Since the radius is one half the diameter, you can then multiply your result by 2 to get the actual diameter of the object that the cable can be safely bent around repeatedly, (for example a bobbin).
In DX-peditions, there is a basic need to unwind the cable and later on to rewind it in the same bobbin (multiple bends). For this operation, needed twice per DX-pedition, please consider 20 times the cable O.D. (this will preserve your cable for a much longer number of DXpeditions).
Solid inner conductor cables, need more attention, even though we have succeeded to make them a little more flexible. The smaller the bend radius, the greater is the material flexibility. Cables such as Ultraflex 7, Ultraflex 10 or Hyperflex 10, having a stranded inner conductor, a strong and flexible 24 spools braid, and an excellent quality PVC jacket, ALLOW MORE, but never infringe the values in the cables datasheets (always to be taken with good sense…careful)!
The diagram above illustrates a cable with a 7,3 centimeter bend radius (Ultraflex 7). When meaning Outdoor use, we intend that the variety of harsh temperatures we could have outside, might change temporarily the physics of the cable components, requiring therefore more cautiousness (20 times O.D.).
In case we need to effect a sharper bend (ex. Like in a choke), we can do only if:
1) We shall effect Just a single bend (possibly always indoor)
2) The operation is made at temperatures never below 15° C (59° F).
3) The cable is coiled over a Cylinder with an O.D. equal or bigger than ten times the cable O.D.