IEC 61158 Cable

Selecting the right IEC 61158 cable for your fieldbus network is straightforward if you follow a few practical steps. The decision hinges on your protocol, environment, and mechanical protection needs.

Start with your protocol. For 31.25 kbit/s systems like PROFIBUS PA or Foundation Fieldbus H1, always choose Type A – a single twisted pair with overall shield, 100 Ω ±20% impedance, 0.8 mm² conductors, and a maximum trunk length of 1,900 m. Type B (multi‑pair, 0.32 mm²) is only for legacy replacements or if you absolutely need multiple pairs in one cable, but it limits length to 1,200 m and has looser impedance tolerance. For PROFIBUS DP, use a 135–165 Ω (at 3–20 MHz) shielded pair. For PROFINET or FF HSE, go with industrial Cat5e/6 or fibre.

Next, decide on shielding and armour. An overall screen works well for single‑pair cables. When running multiple pairs together, choose individual+overall screening to prevent crosstalk. Add steel wire armour (SWA) if the cable will be direct‑buried, laid in outdoor trays, or exposed to impact or rodent damage.

Consider the environment. Check your operating temperature range (standard –40°C to +80°C; high‑temp options available). For chemical or oil exposure, select PUR or special compound jackets. Outdoor runs need UV‑stable black sheaths. For fire‑safe areas, specify LSZH (Low Smoke Zero Halogen). In hazardous zones, ensure Ex‑certification and appropriate blue sheaths.

Always verify key electrical parameters against IEC 61158‑2: impedance, capacitance (low values favour longer distances), conductor resistance, and attenuation. Request the manufacturer’s test report to confirm compliance.

Finally, plan for expansion. Type A gives you the best performance and longest reach – it is the preferred choice for all new installations. If you are unsure, consult your cable supplier with your specific application details, and they can recommend the exact part number that matches your network topology and site conditions.

An IEC 61158 cable is the physical transmission medium used in industrial fieldbus networks—the actual copper or fibre-optic cable that carries digital communication signals between controllers (PLCs, DCSs, or PCs) and field devices such as pressure transmitters, temperature sensors, valve positioners, flow meters, and actuators.

The cable serves two critical functions in modern industrial automation:

1. Data communication – It enables high-speed, reliable digital data exchange between the control system and distributed field devices. For example, in a PROFIBUS PA segment, a single two-wire cable can transmit process values, diagnostic information, and control signals simultaneously.
2. Power delivery – The physical layer defined in IEC 61158-2 allows power to be delivered over the same bus cable to field instruments, eliminating the need for separate power wiring. This is particularly valuable in process automation where field devices are spread across large plants.

Common applications include:

• PROFIBUS PA – Process automation systems, particularly in hazardous areas (Zone 1 and Zone 2)
• PROFIBUS DP – Factory automation, connecting controllers to remote I/O stations, drives, and actuators
• Foundation Fieldbus H1 – Process control systems, using the 31.25 kbit/s MBP physical layer
• ControlNet – Industrial automation networks using coaxial cable

In short, if you are building or maintaining a fieldbus-based automation system, the IEC 61158 cable is the backbone that makes communication between your controller and field devices possible.

IEC 61158-2 defines four cable types (A, B, C, and D) for the 31.25 kbit/s bus used in PROFIBUS PA and Foundation Fieldbus H1. However, only Types A and B are shielded and suitable for reliable fieldbus installations. Types C and D are unshielded, have severely restricted performance, and should be avoided in new installations.

Here is a direct comparison based on the IEC 61158-2 specification:

Quick Selection Summary

Final practical advice: Always verify that the cable’s impedance matches your fieldbus protocol. Using the wrong impedance will cause signal reflections and communication errors. For PROFIBUS PA and Foundation Fieldbus H1, that means 100 Ω ± 20% at 31.25 kHz—which is exactly what Type A delivers.

IEC 61158-2 is the physical layer specification of the IEC 61158 fieldbus standard series. In simple terms, it defines the actual physical medium—the cable, connectors, and electrical signalling—that carries data between field devices and control systems in industrial automation networks.

The physical layer conforms to Layer 1 of the OSI 7-layer model and specifies the media and network configuration requirements necessary to ensure data integrity before error checking at the data-link layer, as well as interoperability between devices at the physical level.

For cable specifiers and engineers, IEC 61158-2 is the most practically relevant part of the standard because it contains the pass/fail criteria for cable performance—impedance, attenuation, conductor resistance, capacitance unbalance, and maximum usable lengths. If your cable does not meet these parameters, your fieldbus network will suffer from signal reflections, data errors, and reduced segment lengths.

The standard covers multiple transmission media, including twisted-pair copper cables (the most common), coaxial cables, and fibre optic cables (multi-mode 62.5/125 µm, single-mode 9–10/125 µm, and plastic fibre 980/1000 µm).