The P-NET standard specifies the use of shielded cable with 1 x twisted pair; this cable type is widely used.

The communication pair must have a characteristic impedance of 100 to 120Ω and a core cross section of minimum 0.22mm² / 24 AWG.

Recommended cable:
LAPP cable ”UNITRONIC® Li2YCY (TP)” 1X2X0.5; (Article No. 0031336): Low-frequency data cable; Core colour code: DIN 47100; PVC; Shielded; Flexible; RS422 / RS485 interface.
Available from e.g.:
Farnell: part No.: 4136658
RS online: part No.: 807-9067

Termination:
We recommend Tubular Crimp Terminals to be used. The white one is made for 0.5 mm2 and fits to the wire pair. The red one is made for 1.0 mm2 and fits to the screen. The cable and Tubular Crimp Terminals are available at the company RS online and picture include their RS item numbers.
The cable is terminated in this way in both ends. It is possible to have two crimp terminal in the same terminal, used when the cable is looped in a bus connected to many P-NET devices.

Shield:
The shield shall not be connected to any chassis or ground, only to the S terminal.
Between the 24V and chassis/ ground electrical noise can appear, depending on how the connection between the minus supply and chassis/ ground is made and where.