At one point I was living in a 6 bedroom home that had cat 6 ethernet wired to each bedroom. The internet connection to the bedrooms furthest from the cable modem had terrible performance, though I don't remember exactly what the symptoms were. Eventually we discovered that the problem was due to using metal staples to fasten the cables throughout the house. I've searched and found a few instructions warning against using metal for ethernet cable fastening, but not an explanation about why. Why do metal fasteners hamper performance so much?
closed as off topic by Ward, EEAA, Jenny D, Dennis Kaarsemaker, Dave M Apr 14 '13 at 15:15
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If you've ever driven under a power line while listening to an AM radio, you probably heard the hum of the cables. At higher frequencies, signals travel in the space around the metal conductor. Theses signals bounce off the metal staples.
If you have enough staples, you wind up with multiple signals reaching the receiver at different times in different phases based on which combination of staples they bounced off of and thus how far they traveled. While the bounces are weak, if enough of them happen to arrive at the receiver in phase and at the same time, they can be strong enough to cause data errors.
Things known to cause problems for Ethernet wiring include: Tight coils, sharp bends, metal staples, long runs parallel to power cables, tight ties, kinked cables, stretched cables, crushed cables, and knots.