Many people believe that if the length of an industrial Ethernet cable is less than 100 meters, signals can be transmitted stably, and only if the length exceeds 100 meters, fiber optic cables are needed. The author has always believed this. It was only after receiving feedback from two customers last year that they found out that flexible Ethernet cables may not be able to transmit stably for 100 meters, especially for high flexibility ethernet cables used for mobile installations, where signal loss can occur even beyond 60 meters.
Case 1：
Last year, an Indian customer purchased a 1500 meter flexible CAT6A Ethernet cable 4x2x0.14mm²（26AWG）. The customer described that all the flexible cables used for fixed installation were used without any problems, and some single cables with a length exceeding 60 meters could stably transmit signals. However, the parts installed in the drag chain that move back and forth may experience signal loss, equipment shutdown, and other situations above 30 meters, while those below 30 meters can be used normally.
The author believes that the part used for the drag chain is due to the repeated bending of the drag chain, which can cause microcracks in multiple conductors. Under the same length, the attenuation of flexible industrial Ethernet cables is greater than that of fixed hard cables. Because the customer is using a flexible Ethernet cable, not a highly flexible Ethernet cable, this model is intended for fixed installation and is not suitable for installation in drag chains. Since the customer replaced the Ethernet cable with a high flexibility Ethernet cable, there have been no malfunctions so far.
Case 2：
In March of last year, a customer specializing in automotive production line integration approached the author, hoping that the author could provide a solution. The customer described their usage as follows: they were also using fixed installation CAT6A flexible Ethernet cables 4x2x0.14mm ² (26AWG), with all lengths below 60 meters functioning normally. However, those with lengths between 65 and 80 meters experienced issues such as servo step loss and camera screen distortion.
Upon the author’s inquiry, it was found that there were many high current power lines in the usage environment on site, and the author determined that electromagnetic interference caused the problem with the high current power lines. The author recommends that customers replace the shielding coverage of 65% of the original Ethernet cable with 90%, which can better shield electromagnetic interference from external environments. The 4x2x0.14mm ² (26AWG) should be replaced with 4x2x0.2mm ² (24AWG), so that even if the signal is attenuated, it can be attenuated less. The customer has been using the solution recommended by the author for over a year now, with stable signal transmission and no malfunctions.
Through the above case analysis, the author has accumulated some experience and drawn some conclusions：
1.Flexible Ethernet cables transmit electrical signals, and the longer the distance, the more severe the signal attenuation and crosstalk distortion; And the higher the speed, the higher the operating frequency, and the more obvious the attenuation amplification.
2.The Ethernet cable used for mobile installation must use a dedicated drag chain cable, and if necessary, use a high-end PUR Ethernet cable.
3.The longer the length of a flexible Ethernet cable, the higher the shielding density and thicker the conductor.