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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?

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closed as off topic by Ward, EEAA, Jenny D, Dennis Kaarsemaker, Dave M Apr 14 '13 at 15:15

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Thanks for the answers. Maybe this question belongs better in superuser. Is it possible to have it moved? –  drs Apr 15 '13 at 14:59
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1 Answer

up vote 7 down vote accepted

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.

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Acts as an inductive choke. Think of the ferrite beads you often find on either end of most VGA cables. They stop RF from flowing in the cable shield. Nasty when you actually want the signal to be transmitted. –  Fiasco Labs Apr 14 '13 at 6:00
    
@FiascoLabs: True, but the problem is more impedance mismatch causing signal reflection than it is excessive impedance causing attenuation. It would take an awful lot of attenuation to make the signal undetectable on the far end. The main problem is if the reflections arrive in phase. –  David Schwartz Apr 14 '13 at 10:22
    
Thanks for the explanation. Bad VSWR, much difficulty... –  Fiasco Labs Apr 15 '13 at 2:27
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