48VDC Positive ground and the WS DC line

[highlands]

At our larger sites we use -48VDC Positive ground systems. This means the positive is tied to earth ground everywhere from the 200 amp incoming power, halo ground system, tower ground and ground rods.
For the UBNT gear we use we go through a Meanwell 48 to 24 power supply which has isolation which is needed as with UBNT gear the coaxial ground and the RJ-45 shielding is ties to the negative of the incoming power.
We wish to use the WS-12-DC as we already have -48 power and hundreds of Ah of battery backup with nothing operating on AC.
How do we integrate this product (easily) into the network?

Sure I can add DC 48 to DC 48 converters for isolation. Please make some suggestions Dave.

John

[Dave]

John

In your situation, indeed the safest thing to do is to put the DC 48 to DC 48 converters for isolation in front of our switch, then you should be good to go.

Dave

[sirhc]

At our larger sites we use -48VDC Positive ground systems. This means the positive is tied to earth ground everywhere from the 200 amp incoming power, halo ground system, tower ground and ground rods.
For the UBNT gear we use we go through a Meanwell 48 to 24 power supply which has isolation which is needed as with UBNT gear the coaxial ground and the RJ-45 shielding is ties to the negative of the incoming power.
We wish to use the WS-12-DC as we already have -48 power and hundreds of Ah of battery backup with nothing operating on AC.
How do we integrate this product (easily) into the network?

Sure I can add DC 48 to DC 48 converters for isolation. Please make some suggestions Dave.

John

I THINK BUT DAVE OLIVE NEEDS TO ANSWER THIS ONE DO NOT USE MY ANSWER

So you will have to flip the polarity into our switch meaning what they originally called Positive will be the DC Negative input to the switch (Black Terminal) and what they originally called Negative will be the Positive input (Red Terminal)into our switch.

Since they bonded their "original" Positive which will now be the DC Negative feed to our switch since your flipping it then it should be OK that they bonded that to the Earth Ground?

Wait for Dave's answer though

[Dave]

Chris/John

I will try & make a more informative post tomorrow, but the basics are if you are hooking up a -48 volt power system to our switch, you need to flip the
connections to our switch (ie..negative to our positive input, and positive to our negative input), but in this way anything that is connected to our switch using POE power will also have the negative side of our switch directly tied to the negative terminal of our switch, which is in turn connected to the -48 volts of your -48 volt system, which if POE device loads (radio's etc) have there power ground connected to chassis ground, means the whole system is "hot" now, which isn't a great idea.

So, if you put a -48 to +48 volts isolation supply in front of our switch, just make sure that the positive output of the isolation supply hooks up to our positive, and negative to our negative terminal.

So, if you put a -48 to -48 volts isolation supply in front of our switch, just make sure that the negative output of the isolation supply hooks up to our positive, and positive to our negative terminal.

Dave

[petecarlson]

I know the switch is already built, but I'm curious as to why you would make a +DC switch instead of a -DC Switch. It is easy enough to wire up a battery bank etc for -DC but not so easy to replace all of the -DC rectifier systems that already exist in the wild.

[RSENG-Eric]

If I'm understanding this right, the input terminals have no internal isolation?

Does the WS-12-250-DC (9-60 VDC flexible input) have the same caveat?

[Dave]

Correct.

[RSENG-Eric]

Do you have plans for a unit with an internally fully isolated DC output? We have a -48V (Return is bonded) setup, and we were about to evaluate the DC switch until I came across this thread. Right now, and I have to use inverters or DC-DC power supplies, and I don't like that.

[Dave]

Under discussions & planning now. Trying to determine market need for it..IE...how many people really need the isolated version.

[petecarlson]

Under discussions & planning now. Trying to determine market need for it..IE...how many people really need the isolated version.

We don't NEED it but it would make life a heck of a lot easier. at 24V mini-pop sites, it really doesn't make a huge difference, but installing at any of our core sites with -48V power systems is a PITA so we have mostly held off on installing Netonix at sites like that.