Issue link: https://www.e-digitaleditions.com/i/1081695
22 I ICT TODAY This requires communication with plant operations and health and safety personnel. Since end devices are often situated in electrical control panels, it is inevitable that the communications infrastructure will need to share this space. Electrical safety codes stipulate that wiring sharing a raceway (e.g., wiring duct within control panels) must have an insulation voltage rating matching that of the highest voltage present within that raceway. Most Ethernet communication cables do not include an insulation voltage rating printed on the jacket or on the cable specification sheet. There are cables available, typically marketed as industrial cables (Figure 2), which clearly indicate voltage insulation rating both on the jacket and in the specification. In light of these factors, a designer is left with two options: keep the communications cable separated from the power wiring with an approved physical barrier, while also considering the physical separation stated in the TIA standards for noise mitigation or use a cable that carries an appropriate voltage rating and a shield for noise mitigation. FIGURE 2: Example of a 600V cable, typically marketed as an industrial cable. a significant level of noise to the media. This issue is highlighted in industrial environments, since there are multiple voltage sources stemming from various transformers and transformer types, both on and off machine, combined with the basic power distribution system transformers that power the building's infrastructure systems (e.g., lighting, receptacles, HVAC). It becomes nearly impossible to ensure a consistently equal grounding/bonding plane across all of these electrical systems. Therefore, at the data enclosure where the infrastructure converges, there are possible voltage potential differences between the ground/ bond at the enclosure, its power source, and that of all equipment to which the cabling connects. ANSI/TIA1005 addresses this situation by detailing maximum voltage potential difference thresholds and the use of a #8AWG minimum bonding conductor run in parallel with the communications cable to create a low impedance pathway for equalizing the difference in voltage potential. The telecommunications grounding and bonding infrastructure can also offer a unique challenge in the industrial environment. Voltage potential difference of the grounding/bonding planes between data enclosures and that of every connected end device must be considered. These differences in potential can result in the introduction of harmful noise into the system. When a shielded copper media is chosen, this can create yet another significant design challenge. The phenomenon, most often referred to as a ground loop (Figure 3), is evident when current flows through the cable shield as it tries to equalize the voltage potential difference; it can introduce A ground loop: something to definitely avoid! Shielded cable Potential between different earth-ground locations FIGURE 3: Always avoid a ground loop. It can lead to current flow between devices through a cable shield and potentially corrupt data transmission and damage hardware.