Plugging equipment into powered port

[keefe007]

I see this giant notice that comes with these switches to not plug a device into a port that is already powered. What happens if this is done?

[sirhc]

sigh, I have made several posts on this so here it goes again. I guess I should provide a link here instead to the other posts but I too am being lazy looking for them! - LOL

We have found at my WISP primarily with the 48VH ports that it "can" cause the switch to reboot.

Possible reasons
1) The RJ45 connector is plugged in at a slight angle and for a micro second there is a short and the poly fuses on those ports will draw far more than 1.2A which causes a power dip that causes the switch to reboot.

2) The inrush to these higher power devices like airFIBER units cause a power dip to the system and causes the switch to reboot.

3) It is a new cable run and the employee crimps it wrong creating a short so when you apply power it is a dead short which can cause the switch to reboot and could damage your radio and or a port in the switch.

So with that being said we have adopted the policy at our WISP that we turn power off to a POE port before unplugging and plugging them in and if it is a new cable, jumper or radio we FIRST run the cable diagnostics to insure there are NO CROSS SHORTS reported. We apply power back to the POE port once the cable is plugged in and or we run a diagnostics on the cable first if a new cable or radio.

If you have a 1G device plugged into the port cable diagnostics should report all 4 pairs as OK and all 4 pairs should report the same length or close to same length.

If you are powering a 100M device like the airMAX radios you should get OK OK for pairs 1 and 2 and SHORT SHORT for pairs 2 and 4 with all 4 pairs the same or close to the same length. Pairs 3 and 4 reporting as "SHORT" is OK as the blue and blue/white wires are shorted together and the same for the brown and brown/white wires, this is NORMAL.

But you should NEVER EVER see a reported "CROSS SHORT" which indicates that an end is crimped wrong.

If pairs are reported at different lengths this is an indication that the cable has been damaged either by being kinked or stretch which causes the pairs to be reported at different lengths.

The fact that you can dead short our ports and you run the risk of damaging the port only is much better then what we found when testing a 48V dead short on the ToughSwitch. Our test almost always resulted in the entire ToughSwitch being fried where as ours at most fried the Ethernet transformer rendering the "PORT" dead but the rest of the switch OK. Maybe you want to test this on one of your ToughSwitches to see if you get the same results?? - LOL

So we are only passing along good practices that we adopted at my own WISP to help avoid problems for you. I recommend you do the same with any POE switch.

But I am warning you that we have randomly seen that when unplugging and plugging in radios that require 48VH that sometimes the switch rebooted and we have no definitive answer as to why as it is NOT easily recreated so we just avoid it anyway.

The cable diagnostics is a good tool to insure cable is not damaged or crimped wrong BEFORE you apply power and find out the hard way!!!

[mhoppes]

I'll add to this that even the top microwave vendors recommend not plugging in licensed (or unlicensed) high draw units to the PoE injector while the injector is providing power.

[wtm]

Might be worth including that as a Note page shipped with the unit! Then we could tag it to the unit after install as a reminder!