Hi,
I’m was the process of configuring and testing a PowerBox RB750UP.
RouterOS = 6.25
Firmware = 3.21
PoE Firmware Version = 2.15

Setup Summary:
Ethernet setup
Eth1-Eth2 are bridged (inside)
Eth3 – disabled
Eth4 – disabled
Eth5 – enabled (outside)

PoE Out setup
Eth2 – off
Eth3 – off
Eth4 – off
Eth5 – auto on

When I power the RB750UP using the DC port (using supplied AC/DC adapter 24VDC-2.5A output), everything is OK, everything works.
I can power up my MikroTik Groove A-52HPn.
Groove bootup power stats:
PoE out Current: 94mA
PoE out Voltage: 23.0V
PoE out Power: 2.1W

Groove steady state power stats
PoE out Current: 77mA
PoE out Voltage: 23.0V
PoE out Power: 1.7W

I could also power up an RB450
RB450bootup power stats:
PoE out Current: 220mA
PoE out Voltage: 23.0V
PoE out Power: 4.4W

RB450steady state power stats
PoE out Current: 170mA
PoE out Voltage: 23.0V
PoE out Power: 3.9W

So I know the RB750UP can power RB450 and a Groove without issue, and both devices are well under the max 1A/port.

So here is the problem – when I power up the RB750UP using PoE in (to Eth1) the RB750UP will power up OK.
BUT it will not power up either the Groove or the RB450 on Eth5.

The Eth5 PoE Out Status was showing: short circuit

I also checked the System>Health to see what the input voltage was – no issue.

After checking my configurations I started swapping Ethernet cables around (although these all worked OK with DC jack input) and then suddenly the Groove powered up…

So what was the issue? – it appears my Ethernet cable (with PoE) to Eth1 was regarded as “too long”, even though it was only 2 meters!?
When I fitted a 1m Ethernet cable to PoE into Eth1 it all worked, Eth5 would PoE out OK.

So after a bit more checking I changed the PoE Global setting:
ether1-poe-in-long-cable =yes
(ref: http://wiki.mikrotik.com/wiki/Manual:Po ... l_settings)

And now I can use any length cable to Eth1 to power the unit via PoE in and get my PoE out.

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I’m just staggered that a 2m patch lead would be regarded as “long” – when I read this initially in the manual I was thinking “long” would be >20meters for example…
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I suggest that http://wiki.mikrotik.com/wiki/Manual:PoE-Out is updated with a small troubleshooting section or note on PoE out “short circuit” PoE Out Status so people don’t waste their time like I just did.

Also it is noted (http://wiki.mikrotik.com/wiki/Manual:PoE-Out):
When: ether1-poe-in-long-cable =yes
“This is potentially dangerous settings and should be used with caution”
How about some more details please, as this seems to be a necessary setting to actually use the RB750UP’s potential especially as you’d expect PowerBox to be used externally and therefore would most likely need to run a PoE in greater than 2m.

Cheers

Also it is noted (http://wiki.mikrotik.com/wiki/Manual:PoE-Out):
When: ether1-poe-in-long-cable =yes
“This is potentially dangerous settings and should be used with caution”
How about some more details please, as this seems to be a necessary setting to actually use the RB750UP’s potential especially as you’d expect PowerBox to be used externally and therefore would most likely need to run a PoE in greater than 2m.

I agree completely. The whole point of the PowerBox (& RB750UP) is moot if you cannot "safely" use more than 2m of PoE-in

i got exact same problem with rb260gsp, after enabling poe1 in long cable all work well...

Same here, powering a RB912UAG, a UBNT RM5 and a RB493.

I'm not sure how your post is relevant to this discussion?

spamerzzzz!

thank you VERY much for your description and the solution! Exactly the same problem we had, and tried everything to find out what is wrong.
And this is 8 years after your post.