According to EIA SP-2840A (a draft version of EIA-568-x) the minimum
     bend radius for UTP is 4 x cable outside diameter, about one inch.
     For multipair cables the minimum bending radius is 10 x outside 
     diameter.

     SP-2840A gives minimum bend radii for Type 1A Shielded Twisted Pair
     (100 Mb/s STP) of 7.5 cm (3-in) for non-plenum cable, 15 cm (6-in)
     for the stiffer plenum-rated kind.

     For fiber optic cables not in tension, the minimum bend radius is 10 x
     diameter; cables loaded in tension may not be bent at less than 20 x
     diameter. SP-2840A states that no f/o cable will be bent on a radius
     less than 3.0 cm (1.18-in).

     The ISO DIS 11801 standard, Section 7.1 General specs for 100 ohm 
     and 120 ohm balanced cable lists three different minimum bend radii. 
     Minimum for pulling during installation is 8x cable diameter, min 
     installed radius is 6x for riser cable, 4x for horizontal.

     For fiber optic cables not in tension, the minimum bend radius is 
     10 x diameter; cables loaded in tension may not be bent at less 
     than 20 x diameter. SP-2840A states that no f/o cable will be 
     bent on a radius less than 3.0 cm (1.18-in).

     Some manufacturers recommendations differ from the above, so it is
     worth checking the spec sheet for the cable you plan to use.