Oddly enough, I don't have continuity from the shield around the Ethernet 
connectors to anything, but the USB and SFP cages as well as the metal around 
the mounting holes (which do nothing on a plastic case with plastic standoffs) 
carry through to the outside of the DC jack. 


I can check what has voltage when I'm back to where I actually have one plugged 
in. 

Now, I won't be using shielded cable, just standard cat 5. I don't know what 
type of isolation there is from standard Ethernet to the negative\ground. I 
just checked and the solder points on the bottom of the board (eight of them 
for each Ethernet) do indeed go to negative\ground. Sounds like that idea is 
out until I can get +48 to the router. 

I can make do by stacking VLANs on the SFP and using the DSLAM or switch to 
move the traffic around, but having one port for east and one for west would be 
nice. 




----- 
Mike Hammett 
Intelligent Computing Solutions 

Midwest Internet Exchange 

The Brothers WISP 




----- Original Message -----

From: ch...@wbmfg.com 
To: "AnimalFarm Microwave Users Group" <af@af.afmug.com> 
Sent: Monday, June 25, 2018 9:12:04 AM 
Subject: Re: [AFMUG] Fw: -48 vDC to 48 vDC 




Yes, the shields around the ethernet jacks. I presume they have a little metal 
tab that would engage with a shielded plug if inserted. 
I think the USB shield should be connected to internal ground as well. 




From: Mike Hammett 
Sent: Monday, June 25, 2018 8:06 AM 
To: AnimalFarm Microwave Users Group 
Subject: Re: [AFMUG] Fw: -48 vDC to 48 vDC 


When you say chassis, I assume the case, but this is a plastic case, so 
something inside? 

https://mikrotik.com/product/RB960PGS 




----- 
Mike Hammett 
Intelligent Computing Solutions 

Midwest Internet Exchange 

The Brothers WISP 




----- Original Message -----

From: ch...@wbmfg.com 
To: af@af.afmug.com 
Sent: Monday, June 25, 2018 8:44:01 AM 
Subject: [AFMUG] Fw: -48 vDC to 48 vDC 







Hard to answer. Power up the MT with it resting on something that is not 
conductive. 

Measure from both sides of the incoming power to the chassis and ethernet 
shield connection. 
If there is no voltage between chassis and shield and either side of the power 
input it is probably a floating load. 
If it is a floating load you can hook it up to any source of 48 volts. 

However, if you measure a voltage from chassis to the positive input, then it 
is a negative ground load and will short out a –48 input. 




From: Mike Hammett 
Sent: Monday, June 25, 2018 7:27 AM 
To: AF 
Subject: -48 vDC to 48 vDC 


I have a Mikrotik hEX PoE plugged into a telco -48 vDC plant by reversing the 
polarity of the power wires. 

Should I expect a cat 5 connection between the router and the DSLAM to cause 
issues? 




----- 
Mike Hammett 
Intelligent Computing Solutions 

Midwest Internet Exchange 

The Brothers WISP 





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