What it is and where it fits
The 6GT2891-4FN20: This is a pre-assembled SIMATIC RF MV plug-in cable, 20 m long, terminated with M12 connectors — male on one end, female on the other, both 8-pin straight. It is the link between an ASM 456, RF160C, RF170C, or RF18XC communication module and an RFID reader, or it can daisy-chain as an extension between those modules and readers in the SIMATIC RF / MOBY family. The 300 V rating covers the signal and power conductors inside the 6-core L-YC11Y construction, and the braided shield (tin-plated copper) keeps noise out of the data pair in an industrial environment. The cable is rated for continuous flexing — 3 million bending cycles at a 75 mm bend radius, with a maximum tensile load of 200 N. That means it is built for moving applications like read/write heads on conveyors or gantries where the cable sees constant motion. The jacket is black PVC, flame-resistant per IEC 60332-1-2, and resistant to grease, mineral oil, and UV radiation. If the line sees washdown or coolant mist, the jacket holds up.
What the ratings mean for fit
The 300 V maximum is the conductor-to-conductor and conductor-to-shield voltage rating. For the signal levels on an RFID reader interface (typically 24 VDC), that is generous headroom. The loop resistance of 160 mΩ/m max and insulation resistance of 20 GΩ·m tell you the signal drop over 20 m is negligible for standard RS-422 or RS-485 levels used in these RF modules. The 6-core count (1x0.25 mm² each, 24 AWG) gives you power, ground, and two differential pairs with spare conductors for auxiliary signals or shield drain. The M12 8-pin straight connectors on both ends are the standard pinout for Siemens RF modules in this generation. No adapters needed if you are replacing a damaged cable on an ASM 456 or RF160C — it plugs straight in. The 20 m length covers most conveyor-line spans; if you need longer, the same cable family offers other lengths, but this one is the 20 m variant.