Siemens SIMATIC NET PROFIBUS Owner's Manual page 137

Note
Stranded cores must only be used in screw terminals with wire-end ferrules fitted
2
(0.25 mm
materials with permanently stable contact properties, for example copper with a
tin-plated surface (not aluminum).
PROFIBUS Networks SIMATIC NET
6GK1970-5CA20-0AA1 Release 2 05/2000
complying with DIN 46228). Use only wire-end ferrules made of
Passive Components for RS-485 Networks
4-39