Selecting Ethernet cables

01 April 2020

Although there is still a myriad of industrial fieldbus protocols used in machine automation, Ethernet is becoming the clear favourite. This is for two reasons; the high data transmission rates support Industry 4.0 requirements and it integrates easily into existing office IT network infrastructure. Justin Leonard, the-chain director, igus looks at points to consider when selecting Ethernet cables for use in dynamic applications.

Ethernet cables are divided into (CAT) categories, ranging from CAT3 to CAT8. While CAT3 is not used widely, CAT5-CAT7 cables are now common. Also derived from it are the Ethernet standard based PROFINET (Process Field Net) and ETHERCAT (Ethernet for Control Automation Technology). 

For fixed installations, standard Ethernet cables can be used. These are relatively low in cost and consist of a solid conductor. For dynamic applications and, especially, when used in an energy chain, it is necessary to use specially developed cables. Usually consisting fine stranded wires, the cable structure is tailored to the movement in the energy chain to ensure secure data transmission is guaranteed over its service life. 

igus chainflex Ethernet cables are designed for permanent movement in energy chains and include 32 different Ethernet cable types in CAT5, CAT6 and CAT7 from 9 different cable ranges for different application areas. Depending on the requirement, outer jackets made of PVC, PUR and TPE can be selected. Each cable offers different performance levels, so that the right cable can be chosen for each application area to achieve the longest service life.

The subject of maximum transmission length of Ethernet cables is often misunderstood. In general, exercise extreme caution, as the maximum cable length can vary depending on the type of cable. A cable for fixed installation always has a lower level of damping than a flexible cable, which is designed for constant motion. As a result, the transmission length of a flexible cable is shorter.

Depending on the cable range, chainflex network cables are mechanically designed for travel distances of up to 400m or more, but the data rate of the bus system decreases with increasing cable lengths. The Ethernet specification describes a total cable length of 100m however, 90m installation cable and 10m patch cable (2x5m) are provided. With highly flexible Ethernet cables for use in energy chains, the recommended maximum length between two Ethernet devices is 50m. However, this length is dependent on the cable category (CAT5, CAT5e, CAT6, CAT6A, CAT7), environmental conditions and application requirements. For long travels fibre optic cables are recommended instead, which are suitable for several hundred metres up to 2km.

All chainflex bus cables have one thing in common - they are assessed to the same quality standards. Whether it is a cost-effective cable of the CF888 range, or a cable for the highest demands and smallest bending radius as is the case with the CFBUS.LB range, they each go through the same test procedures. This is why igus also offers a 36-month functional guarantee on all chainflex cables with service life of up to 10 million double strokes.