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| Levels Lab #8 Electrostatic Discharge and High-Performance Cabling
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| While electrostatic discharge (ESD) from cabling isn’t new, the increasing density of
electronic card circuitry in telecommunications is creating greater susceptibility, which brings ESD under scrutiny.
Electrostatic discharge can cause permanent damage or intermittent malfunction
of networking components, sub-assemblies and fully assembled electronic cards. Any
user—installer, administrator or end user—that touches equipment or cabling becomes a
potential source of ESD into communications equipment. This is primarily a concern for
cabling that has been installed but not yet connected. Cables can become charged when
they’re unrolled and slid over carpet, linoleum or through gloved hands. The charged cabling then becomes a source of ESD to the communications equipment. If the cables are not discharged to an earth ground, electrostatic charges can remain for a significant amount of time, especially in dry conditions.
ESD Testing
Anixter conducted a series of experiments in its Levels Lab ® to determine potential
causes, effects and solutions to ESD problems.
Simultaneously, Avaya Labs conducted a series of tests designed to measure whether
Category 5e and Category 6 cables exhibit greater susceptibility to ESD than the more
common Category 5 cables.
Set-up
Beyond cable design and dielectric materials, humidity and installation practice can more greatly affect charge retention. Relative humidity was monitored, along with the temperature and barometric pressure, to verify that they remain within the specified
test range for the IEC ESD standard. The installation for each cable was performed
in an identical manner. Each cable was laid directly on a ground plane for its entire length, an arrangement that also maximizes the cable's capacitance to ground. The testing method was selected to provide a very repeatable charging and discharging event.
As described in IEC 61000-4-2, a static charge generator was used to inject a 8 kV
pulse into one end of a conductor pair in each cable. Tested cables included an
assortment of Category 5, Category 5e and Category 6 unshielded twisted-pair cables
(each 56 meters in length). A high-speed waveform recorder was used to capture a
digital waveform, recording the charge and discharge as a function of the time interval.
In this manner, a charge retention and discharge profile was obtained for each cable,
in order to provide a clear comparison.
Results
There was no significant charge retention difference between standard-based and
high-performance cabling. It’s important to understand that all cables, whether
Category 3, 5, 5e or 6, have a nearly identical ability to acquire a static charge.
Equipment Guidelines
ESD guidelines are written for the electronics manufacturer, although the intent is for them to be incorporated into the manufacturer’s product documentation as well. Follow all of the equipment manufacturer’s warnings to be certain that the electronic equipment is installed and used according to specifications and guidelines. Assess your site’s susceptibility to ESD. Low humidity and static-generating building materials are the primary cause of ESD phenomena. Mitigation techniques, such as anti-static flooring and humidity control, are important for critical installations.
Recommendations
Working with leading instrumentation and equipment manufacturers, Anixter’s Vice President of Technology, Pete Lockhart, approached ITW Linx about producing several prototypes of simple grounding devices for use with RJ45-style patch panels. ITW Linxmanufactures UL-listed devices to protect equipment connected to voice and data lines. One of the resulting new products is pictured below. The grounding wire lug is bonded to a grounded rack or cabinet, which in turn is connected to the building’s ANSI/TIA/EIA-607-compliant grounding and bonding busbar network. Prior to connecting horizontal or backbone cables from patch panels to active electronics, a patchcord from the panel is inserted into the LAN Static Discharge Unit. Electrostatic charges are drained to the ground. Once connected to active equipment, there is no further build-up of electrostatic charges.
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