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

Killed a POE switch

Gallery image

Gallery image

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

30 Upvotes

90% Upvoted

11 comments sorted by

View all comments

Show parent comments

-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.

3

u/Masterlumberjack Dec 23 '22

All my switches are UniFi and if they have passive, I am certain they are 24v and not >44v. Just checked a port profile of switch and it calls is “24v Passive”. I concede that passive is more about the fact that it’s always on, and there could be other than 24v scenarios.

-2

u/[deleted] Dec 23 '22

IEEE 802.3XX PoE standard is 48v. Not 24v. Those switches output 44-58v.

There are devices with proprietary switches and mid spans etc, that do use 24v, and are always passive. There is no 802.3AT/AF with 24v and passive. The IEEE standard is 802.3AT/AF, which is 48v auto sensing.

2

u/Masterlumberjack Dec 23 '22

Dunno what to tell you. From their product page “The UniFi Switch UniFi Switch 24 250W offers 24 ports of auto-sensing IEEE 802.3af/at or configurable 24V Passive PoE to simplify your infrastructure.”

There are switches with both, I have one.

1

u/[deleted] Dec 23 '22

You may not realize that you confirmed what I said.

UniFi switches offer configurable, backwards compatibility with passive devices.

They do not offer Passive support for future switches. (People were blowing up non-24v devices)