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134 posts

Master Geek


# 254422 11-Aug-2019 18:53
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In trying to diagnose why an in-wall ethernet cable would drop from 1Gb to 100Mb but still work. I noticed for a period after plugging in a cable tester there was stray voltage faintly lighting up a couple of LED on the tester (leds 1&2), the stray voltage is no longer there so the voltage appears to be intermittent.


Is this likely induction from the mains? Whats the best way to diagnose this?


Would this be introduced from wrapping around a power cable or just running along side?


Things to note:


I've only seen this stray voltage once.  Nothing was plugged in either end, other than one end of the cable tester, the cable tester remote without power.


Ethernet speed drops to 100Mb from 1Gb, many times.  I now assume this is from the stray voltage.


There is another ethernet cable running along side it, which it is not having and issues, or at least not I have noticed, as the TV is plugged into this is only 100Mb.


The cable tester stray voltage lighting up the tester is faint at one end and very faint at the other.  I guess that means the stray voltage is introduced at the end with the brighter light. The furtherest end away from the switch.


There is nothing switching on and off that would introduce they stray voltage.







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4201 posts

Uber Geek

  # 2294357 11-Aug-2019 19:28
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Is it running near any large power cables? I highly doubt a standard 2.5mm TPS would be able to induce enough to light an LED.


Are you absolutely certain nothing was plugged in at all?


The most common reason for dropping to 100Mb is simply losing a couple of pairs on the link - either bad pins on the RJ45, bad crimp on your connectors, bad punch-down on the RJ45 modules, etc. My main point being, 99% chance it is just a physical issue and what you are seeing on your tester is just the result of a cheap cable tester.

418 posts

Ultimate Geek

  # 2294377 11-Aug-2019 19:52
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I would replace the cable as it sounds it might be poked.


It could be damaged somewhere along the cable route.

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