XPost: uk.comp.os.linux, alt.comp.microsoft.windows   
   From: dan@djph.net   
      
   On 2025-05-29, Theo wrote:   
   > In uk.comp.os.linux Java Jive  wrote:   
   >> On 2025-05-29 17:34, Theo wrote:   
   >> > Either that or an RJ45 socket at each end and a multimeter.  But the   
   tester   
   >> > makes it quicker.   
   >> >   
   >> > (can't speak for that tester - you need to test for open circuits, shorts   
   >> > and mis-wired pairs and I can't tell if it does that.  In particular if   
   it's   
   >> > structured wiring you need to be able to test from one end because you   
   can't   
   >> > see both ends at the same time as the cable runs through the building -   
   >> > unless you can run a long patch cable back to the start)   
   >> As I understand, the two halves of those testers slide apart and you can   
   >> put one half at each end to perform the test.   
   >   
   > Do you need to see both ends to run the test, or is one sufficient?   
   >   
   > I saw a video showing that a green light on each part scans down the numbers   
   > 1 to 8 then 'G'.  But I'm not sure if you are testing that the lights match   
   > at both ends, or if a fault is only shown at the end that detects it.   
   >   
   > (eg if you had open circuit at one end and a short at the other, what would   
   > it tell you?)   
      
   Yes, you need both ends in order to complete the test circuit; but you   
   can look at them independently. Verification is basically that on the   
   REMOTE end (smaller unit without the battery), the LEDs count in the   
   correct order (1,2,...8,G).  LEDs on the main end (the one with the   
   battery) -- at least in the testers I have here -- are just wired in   
   parallel to the conductor under test, and don't actually provide any   
   insight into the conductor state.   
      
   Note that these LED testers will only find *electrical* faults (crossed   
   conductors, missed terminations, etc.); but the testers can't confirm if   
   the run is actually "good". For example, if it got crushed in a bend   
   somewhere, electrically the cable is OK, but the excessive bend radius   
   may cause problems at gbit speeds.   
      
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