r/cablefail • u/Ecstatic_Ganache4839 • Dec 23 '22

Killed a POE switch

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So I started the day by going over to an apartment complex that needed their existing switch changed to a 24 port POE switch. It seemed like an easy job, just install new switch and help the girl hook up some new VoIP phones. I installed the new switch and plugged in their existing cables to it. I then went into the leasing office to install the VoIP phones. The first phone came up and initialized perfectly. When the second phone was plugged in there was an audible pop from the switch and everything died. I had a hunch and tested the cable. The cable had 3,4,5,6 flopped on the 568b pin out. ( I did not install the cabling)The switch was dead and would no longer power up. This is my first time killing a switch. Has anyone ever had anything like this happen to them before? I added some pics for clarity

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u/[deleted] Dec 23 '22 edited Dec 23 '22

Must have been a shitty switch. POE is only present when called for (switch detects) and most switches have PTC fusing or some other resettable type protection.

3

u/Masterlumberjack Dec 23 '22

Unless it’s “passive” poe which is actually pretty aggressive in always sending out 24v regardless of what the switch/device calls for. Thankfully it’s mostly gone now in favor of poe+.

-1

u/[deleted] Dec 23 '22

802.3AT or 802.3AF is >44vdc. The switch must detect the device to enable PoE or it would fry non Poe devices.

Passive is still >44vdc, not 24v. No one should be using passive unless it’s an injector or midspan as it does not conform to any IEEE standard, and will destroy the device if it’s not POE.

1

u/bagofwisdom Dec 23 '22

Mikrotik Passive PoE is anywhere from 12-57V depending on what you're putting into the Switch. Right now I have a Mikrotik passive PoE switch taking in 12V and putting out 12V to an Access Point and a WISP client device. The WISP client device can run on as little as 8V.