Yep, if you float the load so it has no connection to the environment it doesn’t matter what you connect it to for a power supply as long as the voltage is correct. I have actually bolted metallic chassis load devices to plywood and then put a sign on them saying the chassis in hot in places where we had –48 but negative ground loads.
From: Mathew Howard Sent: Monday, June 25, 2018 9:05 AM To: AnimalFarm Microwave Users Group Subject: Re: [AFMUG] Fw: -48 vDC to 48 vDC This is kind of odd... I was just checking a hEX POE with a meter, and I'm getting 24v (using a 24v power supply) when I check between the positive side of the power input and the SFP cage, or the shield on the USB port, but I'm getting about 9.5v going to the shield on the ethernet ports. I'm pretty sure that the RB750UP/hex poe lite (the non-gigabit version) has the negative side of the power plug tied directly to ground, but these seem to be a bit different. Anyway, couldn't you get around the problem by just using non-shielded cat5? On Mon, Jun 25, 2018 at 9:38 AM, Mike Hammett <af...@ics-il.net> wrote: 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 ------------------------------------------------------------------------------ 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 ------------------------------------------------------------------------------ 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 -- AF mailing list AF@af.afmug.com http://af.afmug.com/mailman/listinfo/af_af.afmug.com ------------------------------------------------------------------------------ -- AF mailing list AF@af.afmug.com http://af.afmug.com/mailman/listinfo/af_af.afmug.com -- AF mailing list AF@af.afmug.com http://af.afmug.com/mailman/listinfo/af_af.afmug.com -- AF mailing list AF@af.afmug.com http://af.afmug.com/mailman/listinfo/af_af.afmug.com -------------------------------------------------------------------------------- -- AF mailing list AF@af.afmug.com http://af.afmug.com/mailman/listinfo/af_af.afmug.com
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