It does kind of get into the messy question of where is your single point ground? If it’s at the top, it would be better to run 4 wires, and connect the 24V and 48V return wires at the top to the single point ground. If you have electronics both top and bottom, things get a bit messy. If you are running a ground wire up the tower to try and maintain a common ground between top and bottom, that’s difficult already without running power supply current over that wire. So it depends on your total configuration. Running just one voltage up the tower and generating any others from that probably simplifies things a little.
If your switch and/or router is at the bottom, and you are running fiber + DC power up the tower for radios, there is also the question of where are you fusing the power? It might be best to individually fuse the radios at the bottom and run individual power wires up the tower, or even to have a small power supply for each radio if these are big guys like licensed links. From: George Skorup Sent: Monday, November 16, 2015 4:38 PM To: [email protected] Subject: Re: [AFMUG] DC question To answer your specific question about using the third wire as the return for both the +24 and +48, yes, it will work. No different than single-point grounding. It's really going to depend on the current required for both systems if that single third wire will be able to handle the 0V return current. But I would agree with everyone else, just run 48/56 up and use DC-DC converters as needed. On 11/16/2015 3:28 PM, Mathew Howard wrote: Yeah, running 48v to the top and then dropping to 24v is what I was planning on doing, but I just got to wondering if the other way would work... the only real advantage being less electronics at the top. On Mon, Nov 16, 2015 at 3:20 PM, Justin Wilson - MTIN <[email protected]> wrote: +1 to this. It’s not the volts you have to worry about it’s the amp drop. DC doesn’t lose much voltage over even a 1000 foot run of 12 gauge. What happens is the wire is not heavy enough to carry the needed amps. There are some calculators that say how many amps a certain gauge of wire can carry at such and such voltage on DC. Most folks we work with are running 10 gauge wire up the tower in these cases. Justin Wilson [email protected] --- http://www.mtin.net Owner/CEO xISP Solutions- Consulting – Data Centers - Bandwidth http://www.midwest-ix.com COO/Chairman Internet Exchange - Peering - Distributed Fabric On Nov 16, 2015, at 4:16 PM, Vince West <[email protected]> wrote: I would recommend using 48v up and down converting to 24v. Depending on how far you are running it, I would recommend doing 48v also to prevent voltage drop. I am not sure you can even do waht you are asking if you are using something like 16-3 service cord. That goes beyond my knowledge. I would personally down convert to power two different pieces of equipment. Vince West Tower Hand Technical Support Shelby Broadband 148 Citizens Blvd Simpsonville, KY 40067 Phone: 1-888-364-4232 On Mon, Nov 16, 2015 at 4:07 PM, Mathew Howard <[email protected]> wrote: If I have a three conductor cable running up a tower, would it be a work, or be a bad idea, to run both 24v and 48v through the same cable and use the third conductor for the return on both?
