Siemens Fiber Optic Cable Selection: PROFIBUS and PROFINET Guide

Overview: Industrial Fiber Optic Cable in Automation Networks

Fiber optic cables (FOC) replace copper conductors in industrial plants where high electromagnetic interference (EMI), long distances, electrical isolation, or potential equalization problems make copper transmission unreliable. In Siemens automation systems, fiber optic cable is used for three principal applications:

• PROFIBUS DP/FMS fieldbus networks bridged by Optical Link Modules (OLM) such as the 6GK1502-... OLM/G12 V4.0 series, which convert electrical RS-485 segments into optical segments.
• PROFINET industrial Ethernet using SCALANCE X/XB/XC/XR switches with integrated fiber ports, plus media converters when a single media change is needed.
• SIMOLINK SLB (SIMOLINK Board) drive synchronization rings for MASTERDRIVES, SIMOVERT, and SINAMICS S120, where an FO ring carries the 37-bit SIMOLINK frame between drives.

Selecting the correct FOC requires the engineer to fix four variables up front: the protocol (PROFIBUS DP at 9.6 kbit/s to 12 Mbit/s, PROFINET 100 Mbit/s / 1 Gbit/s, or SIMOLINK 11 Mbit/s), the physical port on the active device (BFOC, SC, SC-RJ, LC, duplex, simplex, MT-RJ), the segment distance, and the environment (indoor cabinet, trailing chain, outdoor, hazardous area).

Fiber Optic Cable Types

Siemens cataloged FO cable falls into three families, each with distinct attenuation, bandwidth, and mechanical properties.

Glass FO Cable (Multimode and Single-Mode)

Glass FO cable is the highest-performance medium. It is divided into multimode (MM) fibers with a 50 µm or 62.5 µm core, and single-mode (SM) fibers with a 9 µm core. Multimode glass fiber is the standard for PROFINET/SCALANCE links up to 5 km at 100 Mbit/s, while single-mode is reserved for long-haul runs from 10 km up to 70 km with the appropriate LH (Long Haul) or LH+ optical modules.

Key specifications:

PCF FO Cable (Polymer Cladded Fiber)

PCF cable uses a glass core (typically 200 µm) with a polymer cladding. It is the workhorse for in-plant PROFIBUS OLM links where cost and field termination matter more than extreme distance. PCF is field-installable with the Siemens PCF termination kit and is supplied as duplex zipcord. Typical attenuation at 660 nm is 10 dB/km. Practical segment length is up to 400 m between OLMs (G12) and up to 300 m with OLM/G11.

POF FO Cable (Polymer Optical Fiber)

POF cable (980/1000 µm) is a 1 mm plastic fiber. It is the lowest-cost FO medium, easy to terminate with a simple cleaving tool, and immune to many mechanical hazards because of its large core. POF links are used for short PROFIBUS OLM segments (typically up to 80 m with OLM/P11, up to 400 m with P12) and as drop cables to optical PROFIBUS devices with an integrated Simplex socket. POF cannot be used for PROFINET — its bandwidth-distance product is too low for 100 Mbit/s Ethernet.

Optical Connector Types Used with Siemens Equipment

Each Siemens device family specifies a fixed optical socket. Cross-wiring a wrong connector family is the single most common commissioning error and produces a faint light at the far end that does not decode as data.

Notes on the table:

• BFOC and ST are physically identical; the older Siemens designation BFOC (Bayonet Fiber Optic Connector) is the IEC 61754-2 standard for this interface.
• SC RJ is not the same as an RJ45 plug — it has a 1.25 mm ceramic ferrule like LC and is keyed to avoid confusion with copper RJ45 jacks.
• Of the Siemens network components, only RUGGEDCOM devices use MT-RJ sockets. The prefabricated RUGGEDCOM cables have fixed part numbers and should be specified by reference, not built in the field.

Siemens RUGGEDCOM MT-RJ Cables (Article Numbers)

When the project specifies RUGGEDCOM equipment, use the approved prefabricated cables. Field-built MT-RJ is not supported in the field-service procedures.

The trailing 8BA0 / 6AA0 suffix encodes length and color. The base article number with the -8BA0 family is MTRJ to MTRJ, while -6AA0 crosses LC (PROFINET SFP side) to MTRJ (RUGGEDCOM side). Always confirm the active order code in the Siemens Mall or Industry Mall at the time of order, since part-number ranges are revised.

Siemens Fiber Optic Cable Article Numbers for PROFIBUS and PROFINET

Siemens sells both prefabricated cable assemblies and bulk cable. The most commonly ordered items for green-field PROFIBUS and PROFINET work are:

Selecting Between Single-Mode and Multi-Mode

The decision is dominated by segment length and the optical budget of the active device. Use the following decision path before ordering cable.

1. Determine the segment distance including service loops (allow 10 m extra per end for splice trays).
2. Add connector loss: 0.5 dB per mated pair, 0.3 dB per splice.
3. Read the optical budget of the SFP or fixed optical port. SCALANCE X-200 with integrated multimode port: typical transmit power -9.5 dBm, receive sensitivity -20 dBm, budget 10.5 dB. SCALANCE LH single-mode: budget up to 28 dB depending on module.
4. Compare budget × distance to the cable attenuation:

Single-mode is the only option for long-haul backbones. Multimode is the default for plant floor. PCF is the budget choice for medium PROFIBUS runs. POF stays inside the cabinet or between adjacent cabinets.

SIMOLINK Optical Ring Specifications

SIMOLINK is a proprietary Siemens fiber ring used for drive-to-drive synchronization on MASTERDRIVES, SIMOVERT MASTERDRIVES VC/MC, and SINAMICS S120 systems. The SLB (SIMOLINK Board) is installed in the active line module or in the SIMOLINK-capable control unit, and the ring must be closed for the system to start — a broken ring generates F08501 / F08502 on the connected drives.

How to Order Fiber Optic Cable

1. Identify the protocol (PROFIBUS, PROFINET, SIMOLINK, ASI, RUGGEDCOM) and the device family that terminates the fiber.
2. Read the optical port type printed on the device: BFOC, SC, SC RJ, LC, Duplex, Simplex, or MT-RJ. Substitute decisions at this step are not safe.
3. Measure the route length and add 10 m for service loops and slack at splice trays. Add 0.5 m for POF/PCF field termination ends.
4. Choose cable family by environment: Standard for cabinet, Trailing for cable carriers, Torsion for robots, Marine for shipboard.
5. Order bulk cable plus connectors (more flexible) OR order a prefabricated assembly by article number (lower risk). For RUGGEDCOM, always use prefabricated assemblies 6GK6000-8GD00-8BA0 (MTRJ-MTRJ) or 6GK6000-8GD00-6AA0 (LC-MTRJ).
6. If the route requires field termination, order the matching termination kit and a sufficient stock of crimp rings, polishing films, and an OTDR or power meter for verification.

Termination Procedure: Field-Installable POF / PCF Connectors

The IE FC SC-Plug (6GK1901-1BB10-2AA0) and the IE FC BFOC-Plug (6GK1901-1BB10-2AB0) are the standard field-installable connectors for PROFINET and PROFIBUS. The procedure below is the field-proven sequence.

1. Strip the outer jacket of the cable by 30 mm with the adjustable stripping tool supplied in the FC termination kit.
2. For POF: polish the 1 mm core with the 1000-grit film, then the 5 µm film, then the final 0.3 µm polishing film, finishing in straight strokes only.
3. For PCF: cleave the 200 µm core with a precision cleaver; do not polish — the cleave is the optical surface.
4. Crimp the connector body onto the cable with the FC crimp tool. A ratcheting crimp is required — hand-crimping will give intermittent faults.
5. Inspect the ferrule endface at 10× magnification. A clean POF face appears mirror-bright; any scratch over 5 µm disqualifies the connector.
6. Plug into the device and execute a tug test. Per the IEC 61300-2-4 test method, apply 5 N axial load for 5 seconds; any movement fails the test.
7. Measure insertion loss with an optical power meter (850 nm / 1300 nm source matched to the operating wavelength). Acceptable loss: < 1.0 dB per mated pair on multimode glass; < 2.0 dB on PCF; < 3.0 dB on POF.

Identifying and Repairing a Damaged Cable

Fiber optic cable fails in three ways: bend loss (cable pulled around a 30 mm radius), connector contamination (dust, oil, or skin acid on the ferrule), and fiber break (crushed, cut, or rodent damage). Use the following triage matrix before pulling a new cable.

Step-by-Step Repair Procedure

1. Prepare tools: diagonal cutters, FC stripping tool, FC crimp tool, cleaver (PCF) or polishing kit (POF), OTDR or fiber-optic power meter, click cleaner, magnifying loupe.
2. Identify the damaged section with an OTDR (event marker at the break point).
3. Cut the damaged section with diagonal cutters, leaving enough cable on both sides for the splice tray.
4. Strip the outer jacket to expose 50 mm of bare fiber on each side.
5. Terminate both ends with the appropriate connector (steps 1–6 of the field termination procedure above).
6. Join the two prepared ends with a one-way in-line splice (POF) or a fusion splicer (PCF/glass). Mechanical splices are acceptable for POF/PCF; fusion splices are required for glass multimode with targets below 0.1 dB splice loss.
7. Tug test: pull both sides with 5 N for 5 seconds.
8. Power meter test from the active device: confirm receive level is within the SCALANCE / OLM sensitivity window.
9. Energize the network and verify cyclic diagnostics for 1 hour before handover.

Verification: Acceptance Test for a New FO Link

Before commissioning, capture the following data and store it in the plant documentation system:

• OTDR trace at 850 nm and 1300 nm (glass) or at 660 nm (PCF/POF), with event table.
• End-to-end attenuation budget: cable attenuation + splice loss + connector loss. Compare to the device's optical budget.
• Bit error rate test for PROFINET at 100 Mbit/s for 10 minutes (no errors allowed). For PROFIBUS, run the bus at 12 Mbit/s for 10 minutes with all slave diagnostics enabled.
• Bend-radius audit: the entire route ≥ 30 mm for glass, ≥ 25 mm for PCF, ≥ 20 mm for POF.
• Connector endface inspection report saved as PDF per IEC 61300-3-35.

Frequently Asked Questions