R&M Data Center Handbook

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Immunity against electrostatic discharge
This test in accordance with EN 61000-4-2 checks the immunity of a system against electrostatic discharge. This
phenomenon, which we all know from everyday life when a spark jumps from our finger to a conductive surface,
can be generated in a reproducible manner with a test rig with metallic test fingers. Environmental and climactic
conditions – such as low humidity, insulated plastic floors and clothing made of synthetic fibers – can promote
electrostatic charging.
The test points were selected to simulate normal contact of the cabling during operation and maintenance. At
each test point, 10 sparks per polarity were generated with a separation of more than 1 second. The test levels
used were set in accordance with the MICE table (see Figure, “Electrostatic discharge – contact / air”).
The shielded cabling systems did not show sensitivity to electrostatic discharges; no faults arose. With unshielded
cable, the active devices reacted in a very sensitive way to discharges as soon as these could impact on the
signal conductors.
The good performance of shielded cabling can be attributed to the fact that the shield can serve as a bypass path
for the flashover and in this way no energy could make its way inside the cable. For 10GBase-T operation with
unshielded cabling, additional measures must ensure that no electrostatic discharges can take place. Suitable
protective measures are well known in electronics manufacturing and can include grounding stations, ESD wrist
straps, antistatic floors, etc.
Summary
It has been shown that the introduction of 10GBase-T in fact has a considerable impact on the selection of cabling.
The increased sensitivity of 10GBase-T transmissions compared to 1000Base-T was clearly evident with unshielded
cabling in terms of immunity against external interference.
In order to guarantee the operation of 10GBase-T, it is not sufficient to pay attention to the cabling alone, rather
the environmental conditions must also be considered and the cabling components must be properly selected.
Coupling attenuation can serve as a qualitative comparative parameter for the EMC behavior of cabling.
Summing up, this investigation has shown that shielded cabling for 10GBase-T can be used without any problems
in every environmental class. The following applies: The better the quality of the shielding, the smaller the emissions
and the better the immunity of the cabling against external interference.
Unshielded cabling, in contrast, is suited for use outside residential areas only and in conjunction with additional
preventive measures for the use of 10GBase-T. Within the EU, this cabling shall be used only outside residential
areas, in dedicated work areas (like offices, data centers, etc.).
In choosing between shielded or unshielded cabling for 10GBase-T, the influences and applications of additional
protective measures and operational limitations must be taken into consideration.
Recommendations for the operation of 10GBase-T
In industrial environments (Classes E2 and E3), shielded cabling should be used. In harsher industrial environments
(E3), an S-FTP shield design with braided overall shield is necessary and, if possible, a double-sided
grounding should be applied to the cabling.
In residential areas, unshielded cabling should not be used. In office areas and data centers with unshielded
cabling, the above-mentioned additional protective measures should be applied.
Page 154 of 156 © 08/2011 Reichle & De-Massari AG R&M Data Center Handbook V2.0