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I have to put some equipment a long distance from a power source and have been looking into this and believe I have the correct solution in mind but would appreciate some input.


I need to place the following equipment 800 feet from a power source - outdoor up a hill.

- (2) PBE-5AC-400
- (2) NBE-5AC-19
- (1) R5AC-Lite

I calculate this at a max power usage of 45.5 watts - or 1.9A at 24 VDC. I believe it is highly unlikely that we will be running anywhere near max power as 1 link is a mile and the other is only 800' (dual radios for each link).

I have 24 VDC power at the source and am planning on running either 10/2 or 12/2 UF-B cable in flexible conduit from the power source to the remote location [up the side of a steep hill].

If my math hasn't failed me I would expect power at the remote location to be (using max power values to be safe);

AC Power
12/2 wire = 4.82 v drop for 19.18 vdc available
10/2 wire = 3.03 v drop for 20.97 vdc available

Battery Backup (21.5v cut off - 2.12 A draw max)
12/2 wire = 5.37 v drop for 16.13 vdc available
10/2 wire = 3.38 v drop for 18.12 vdc available

Ampacity
12 AWG = 20 Amps at 60 °C

10 AWG = 30 Amps at 60 °C


The WS-8-250-DC can accept 9-60 VDC - which even at worse case of 12/2 & battery it would get 16.13 VDC input. It would seem that even if we ran two switches at the remote location (off the same wire) and split the redundant radios between the two switches we should still be well within acceptable limits.

Is there something that I missed in this calculation or perhaps a misunderstanding that someone else sees - or does it look like the WS-8-250-DC switch would do the job here?


A second alternative we've considered is to put in a couple of SD-200B-48 units to step up to 48 VDC

AC Power [0.95 A draw]
12/2 wire = 2.41 v drop for 45.59 vdc available
10/2 wire = 1.51 v drop for 46.49 vdc available

Battery Backup
When on battery the SD-200B-48 will continue to step up to 48v until battery is shut off so calculation at remote site are the same.

This would seem to indicate we could utilize one or a pair of WS-6-MINI switches which can accept 37-53 VDC up to 2A which we would be well within. We'd simply wire up a barrel connector to the switches for power.


The reality is that we will probably run 10/2 instead of 12/2 as the difference in cost is around $100 and for that might as well, but I'd really like to ensure that my thought process on this is right regardless of the cable choice.

you are correct regarding the amount of voltage drop that you calculated.

my only concern would be what is the peak power that your devices might use, and what if they "peak" at the same time? If your max number is considering the "peak" power of the devices I think you are good to go.

I am also concerned about a ground potential difference which will tear up your gear.


The biggest problem with grounding is the fact that too many people think ground is ground and this is simply NOT true. A good grounding system will allow you to once again enjoy the beauty of a good lightening storm.

Your entire system needs to share the same ground potential meaning everything must be bonded with a dedicated copper ground system that is shorter and less resistive ground path than your Ethernet cable path to ground and do not reply on steel towers as your ground path because that ground path is a MUCH higher resistance than you copper Ethernet cable

Storms do cause damage but most times that damage is from the wind (static) and water which changes the ground potential of poorly engineered/implemented grounding systems not ESD or direct strikes.

If you have 2 distinct grounding systems and you have an Ethernet cable running between them you are going to destroy equipment.

Even good grounding systems need annual inspection and maintenance when required from corrosion and such.

Running Etherent cable between 2 locations that have differnt grounding systems is a terrible idea and equipment loss will result.

If taking electric from a service more than 30' from your tower bonding the grounding system is not a good idea and you only want to bring the hot and neutral and simply use the tower grounding system as your AC receptacle Earth Ground (see last link below for a diagram).

A ground potential difference can be low voltage HIGH amperage that will tear up components as it will either pop it immediately or break down the component over a short time.

Many of Ubiquiti 10/100 equipment has DC negative bonded to the Earth Ground meaning the DC circuits are not isolated and all if their equipment that uses the circuit that allows POE brick default will also cause issues when ground potentials exist by allowing DC negative to be bonded to Earth Ground (not an isolated circuit) allowing this ground current into the DC circuits. Best solution is to have GOOD well thought out grounding system to make sure this design does not cause issues.

Excess voltage or current from poorly bonded grounding systems will cause Ethernet Errors as discussed in link 1 below.

Here are some good posts on grounding:
http://forum.netonix.com/viewtopic.php?f=30&t=1816
http://forum.netonix.com/viewtopic.php?f=30&t=188
http://forum.netonix.com/viewtopic.php?f=30&t=1429
http://forum.netonix.com/viewtopic.php?f=17&t=1786&start=30#p13447

eomedia wrote:I have 24 VDC power at the source and am planning on running either 10/2 or 12/2 UF-B cable in flexible conduit from the power source to the remote location [up the side of a steep hill].

. . .

The WS-8-250-DC can accept 9-60 VDC - which even at worse case of 12/2 & battery it would get 16.13 VDC input...

I don't know why you would run with 24V given that the upper limit is 60V unless that is all that is available to you. Can you not put in a 48V supply? Double the voltage, half the amps.

Actually all Rev F can accept 9V to 72V

So i'm looking at doing something similar but it will be from the 5th floor to the roof of a building. On the roof i'm going to just start of some AF5X..... but will want to change that to AF11X or something similar or maybe a AF24HD and then add a backup of similar radios...... It's suppose to be around 800 feet...... what would be the best way to power the distant end with no local power source on the roof? Of course i will be using Netonix switches but best way to power them.