The inconspicuous brake in network cables

Author: Isha Jain

In many networks, there is an inconspicuous brake on data traffic. R&M explains the situation. The often unrecognised vulnerability in local area networks (LANs) is due to certain effects of electrical resistance. Experts know this phenomenon as resistance unbalance in copper cabling. Problems increasingly occur where companies use their LAN untested for Power over Ethernet. R&M explains the background in a video and a white paper, where measurement methods, the technological solution developed by R&M and criteria for selecting patch cords are presented.

PoE needs suitable cabling

Power over Ethernet (PoE) is experiencing a boom. Sales of PoE-capable devices are increasing by 20% annually. Due to this strong demand, infrastructure specialist R&M feels compelled to provide information on key technological aspects.

With PoE, modern terminal equipment can also be supplied with power in the LAN. Current and data flow via a single ethernet network cable. This saves additional electrical wiring for terminal equipment such as WLAN connection points, sensors, surveillance cameras and many other smart building systems.

Companies often use the existing LAN cabling for new PoE applications without first testing whether that works. They also use existing or inexpensive patch cords to connect the PoE devices. However, the demands on the LAN cabling increase when high-speed data transmission and PoE have to work together with high currents. This is why it recommends checking the LAN separately before constantly using higher PoE categories (4PPoE). According to R&M, users have to make sure that their structured cabling is PoE-ready. It is an absolute prerequisite to have a grip on the resistance unbalance in the entire LAN-transmission channels including patch cords.

The most common risks are associated with patch cords with IPC contacting (insulation piercing contact). These are the findings of tests at the R&M laboratory in Wetzikon. Piercing contacts can age quickly and in different ways. This can lead to resistance unbalance over time. Ethernet data transmission is very robust against these types of errors and the existing problem is thus often not detected. In contrast, the use of PoE can very quickly lead to saturation effects in the transmitters of the active devices and thus to a total failure of data transmission. This is exacerbated by the fact that this unbalance develops over time and the problems are often only identified during operation.

R&M explains that patch cords with piercing contacting are not suitable for PoE transmission over long periods of time and at higher power levels. It also recommends the use of patch cords with insulation displacement contact (IDC). IDC ensures a permanently stable, low-resistance contacting of the copper conductors. As a rule, no resistance unbalance occurs over the lifespan of the IDC patch cord.