POE Polarity on ePMP and PMP450 SMs

Hi all,

Is there a list of which SM models are polarity agnostic? I know most of the newer ePMP models are now but it'd be great to have a list to refer to!

Also I've read that 24V is doesn't work on some SM models even though they say 20-32V on the spec sheet. Can anyone confirm this? 


Below isn't an exhaustive list, just what I remember off the top of my head.  There may be slight inaccuracies.

ePMP 1000 2.4Ghz

Radios are polarity agnostic (all of them that I'm aware of).  The GPS sync AP needs a minimum of 24v to operate though.  The GPS AP will run on 48v as well.  The connectorized radio with two ethernet ports does reverse polarity out on the 2nd port regardless of how you feed it.

ePMP 1000 5Ghz

  • Force 110 (connectorized with dish and 10/100 ports) only takes "cambium" reverse polarity.  Also does reverse polarity out on the 2nd port.
  • Force 180 and 200 are polarity agnostic.  It's possible that some earlier ones only take reverse polarity.
  • GPS sync connectorized radio needs minimum 24v but is polarity agnostic.  Will also operate @ 48v.

ePMP 3000

  • The force 300 units are polarity agnostic except for early 300-25 units that only accept reverse polarity.
  • 3000 CSM is agnostic and 24v
  • 3000L AP is 24v - Don't feed it 48v.  Polarity agnostic.
  • 3000 AP is 48v and averages 14~15 watts with BSA attached and operational.

PMP 450

All SMs I've ever touched only take reverse "cambium" polarity.

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"3000 AP is 48v and averages 14~15 watts with BSA attached and operational."

But is it polarity agnostic ?  I had assumed it was but could be kind of expensive to test and find out it isn't.

The 3000 AP is 802.3AT compliant, so it should be polarity agnostic per the 802.3 spec.

Thanks for that! 

Any idea how to tell if a Force 300-25 is an earlier version that's polarity agnostic or not? We have quite a few of those here.

I used a PMP450b today with an edgerouter poe switch and confirmed that it was indeed polarity agnostic. I know the older PMP450d SMs are not however. 


I don’t know of any way to tell other than plugging one into a ubiquiti power supply and seeing if the lights come on. In my experience the 24v Ubiquiti power supply will not harm it nor will a mikrotik POE switch (have plugged older non agnostic F300-25’s into both of these with no ill effects) it just won’t work. I’m not sure about other power sources.

Just to add to the confusion, all epmp radios (except the 450’s, not tested yet) (AP and SM) will boot and run on as low as 11vdc (tested) The problem is the current load on the ethernet cable exceeds the 50% rules and in some cases can cause connector heating which is not seen at higher voltages due to lower current flow.

I can confirm that a non-polarity agnostic radio will just not even light up if on the wrong power supply as long as you do not exceed the 32v TVS diode (basically a one way fuse) that is inside. UBNT power supplies and LPUs are fully compatible including the ones with the factory reset button on the psu.

The ePMP 1000 GPS radio won’t run at below 22~24v. I don’t remember specifically the cut-off voltage, but it’s something that I’ve had come up at a few solar sites when batteries got too low. It may partially boot, but it won’t function correctly. The other ePMP radios seem to do fine at lower voltages as long as cables are short.

Voltage drop is a factor, but they do boot and function at lower voltages.

Keep in mind that as a battery depletes the voltage doesnt drop off as fast and the internal resistance inhibits current flow as the potential drops. 24v systems are dead at 21v, 12v systems are dead at 10.8v. These are the points where you can measure potential but current flow is abysmal.

Solar sites can be a pain simply due to measure potential but very little to no current flow.