2

We use a lot of midspan PoE injectors here, rather than PoE switching1, and I recently burned out my third cable tester in the last 2 years by accidentally plugging into a line with an active injector.

Now I need to replace it, and I'd like to do a little better this time. This is just a basic continuity tester of the type that sells for < $10 on Amazon. I know I could spend a lot more on something fancy, but I'm still looking for a more basic device... I just want it to be able to survive the occasional PoE event.

The problem is I don't know what to look for.

What should I watch for in a product description or spec sheet for a cable tester that would tell me it's safe to plug into line with active PoE2?


1. That's another story... we're slowly changing this, but only as switches reach end of life, which is not fast.
2. I am well aware of Stack Exchange's long-standing practice against shopping questions, which is why I'm asking a "what feature to look for" question rather than a "what specific product to buy" question.

  • Since you have to tester to both ends of the cable to test it, how are you "accidentally" plugging it onto a line with an injector? – Jesse P. Mar 7 at 14:21
  • It's not that hard. You go to troubleshoot a computer issue, plug the remote end at the cable by the computer. Then go down to the switch and connect the tester there (or vice versa), and suddenly you find out there was injector somewhere over near the computer for powering a phone. – Joel Coehoorn Mar 7 at 16:53
  • Gotcha. So, the issue is partially that you aren't aware of who has an injector and where they're in use. – Jesse P. Mar 7 at 16:56
  • Usually I'm aware (as the one who placed it), but also just forget until about 1/2 second after I plug in the tester. Again, 3 in 2 years isn't all that often... just enough to be annoying. – Joel Coehoorn Mar 8 at 19:48
  • Yeah, I hear you. I've forgotten where injectors were placed above ceiling tiles, and had to go lifting up tile after tile to find them. – Jesse P. Mar 8 at 19:53
2

What should I watch for in a product description or spec sheet for a cable tester that would tell me it's safe to plug into line with active PoE?

It may seem like a simple answer, but a cable test tool that is capable of testing PoE. Specifically, I would look for a tester that can test the standards (802.3af, 802.3at, and possibly 802.3bt) as well as passive power.

There are some testers in the $100-200 range that do this as well as a number of other tests. Most of the ones I have seen are small projects with "questionable" development cycles, are more "consumer" quality hardware, and tie into some sort of smart phone application.

Push your price point to the $500-1000 range and there are a number of go to professional testers that will do everything you need. These are stand alone devices and usually fairly rugged (so will stand up to some abuse). Often if they do get damaged you can also get them repaired by the manufacturer for less than it costs to get a new one.

And of course, if your budget gives you flexibility to look in the $1000+ this brings you into the realm of advanced diagnostics/troubleshooting tools and/or full certification testers.

Of course, you can probably find used versions of the above for cheaper.

Alternatively, you could consider a standalone PoE test device. I have seen those for as low as $20-50 and you could use this to check for PoE before using your cheap tester. Of course, I don't recommend this route as it would be a hassle/extra work and a better device will give you much more information.

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  • I'm looking for a very-slightly-more-durable replacement for a basic $10 tester. None of this really helps :( – Joel Coehoorn Mar 8 at 19:49
  • @JoelCoehoorn, get a $20 PoE tester and use it before you connect your $10 tester. If you are asking for $10 testers that are PoE safe, I have never seen one and don't expect it to exist. – YLearn Mar 9 at 22:40
  • I know, but if I can buy a $20 PoE tester and $10 continuity tester, surely somewhere there exists a single $30 (not $100+) continuity tester that's at least PoE safe. – Joel Coehoorn Mar 9 at 23:57
  • @JoelCoehoorn, continuity is a simple test - do electrons flow across a medium. There is no signaling or anything more advanced than detecting if a circuit is open or closed. Building the electronics to test continuity while dealing with PoE (i.e. impeding the flow of electrons) is a bit more complicated than just "merging" the two. You may find such a tool out there, but I would expect it to be at least double the $30 you think it should cost and at that price point, having a tool for a few $ more that does more than continuity just makes sense as continuity is not reliable for networking. – YLearn Mar 10 at 0:18

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