Lots of different reasons for grounding and shielding. Electrostatic shielding, magnetic shielding, faraday shielding etc. Lightning routing, ground loop prevention etc etc.
Some of these things are mutually exclusive. I have many customers that use my surge suppressors at the top and bottom of the tower, with shielded cable, to good effect. My products have shielded jacks so they automatically interface with the cable shield and drain wire if you are using the shielded plugs. Some radios expected to be grounded, some expect to float. And when lightning comes, sometimes it comes from the power lines, sometimes from the ground, sometimes it is just induced currents from nearby strikes. Then of course there is the direct hit. Nothing survives the direct strike. With radios, antennas, power lines, network cables and tower steel all involved in different configurations on each tower, hard to do a true R56 common point grounding design. Much easier if it is just coax and antennas on the tower. Personally I would ground top and bottom. And I would use my surge suppressors... for both DC and data. From: Paul McCall Sent: Wednesday, October 26, 2016 3:35 PM To: af@afmug.com Subject: [AFMUG] UBNT S16 Application and AP grounding question Guys, Looking for opinions. I am brave at least. I have reached out to Cambium for opinions and are working with their engineers and just now sent an email to UBNT as well. We are using the S16 with both UBNT and Cambium devices (various APs / BHs) always with the S16 placed at the top of the tower with Fiber / DC up the tower, with a combination of Ditek surge protectors (at the bottom) and Polyphaser surge proectors (at the top) of the DC run. We are grounding the S16 to the tower, and whenever the radios have ground lug, are grounding those to a common “ground bus bar” at the top of the tower as well. Almost every Cat 5e cable that connects from the S16 to the AP/BHs is less than 20feet. My questions are in the area of the Cat 5e cable and grounding, along with surge protection. We are using shielded Cat 5e cables to each radio and shielded connectors at both ends. However, a grounding consultant says to not connect the shield at the end near the S16, rather, peel enough back to ground that to the tower. Does that make sense? Also, if using the drain wire on cable such as ToughCable Carrier, does that make sense? Second question, If we have two different levels of APs / BHs (for vertical separation front/back ratio reasons) , and say each one is 15 feet above/below the S16, should the ground of the radios in relation to this be as close to each level (separate bus bar) as possible or all to one point? Pictures attached. Concerned with the concept of single point grounding vs the concept as grounding as close to the equipment as possible. Lastly, In my scenario of the S16 with relatively short cable runs, does inline Ethernet surge protection make sense? Does it add value to the protection or not really? Its not a $$ consideration vs two more points of failure (protector itself and the extra Cat 5Cable in the middle. With all the $$ that PDMNet has put into not just equipment and fiber retrofits, and extensive sub 5 ohm grounding systems on all towers and electrical panels, additional electrical panel protectors, circuit protectors, etc., I want to close the loop on this last set of details up top. Thanks! Paul McCall, President PDMNet, Inc. / Florida Broadband, Inc. 658 Old Dixie Highway Vero Beach, FL 32962 772-564-6800 pa...@pdmnet.net www.pdmnet.com www.floridabroadband.com
