shorthairedp
join:2005-11-21
united state
| Grounding dos/donts,
I know this is a dead horse, but I need to know. It would be nice if there was a sticky thread about it. Grounding, best practices, how to make it cost effective, how to do it, and most importantly, how to test it.
We have a lot of grain elevator installs just grounded to the frame of the structure, is this sufficient? What about on top of concrete grain elevator, is bonding to some conduit for ground sufficient?
How do I easily test the quality of ground, 150 feet in the air? |
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AMD Phreak
Premium
join:2003-12-14
1 edit | Well without specialized training from trainers or someone in your organization that has had this training, or manuals and books on the subject it's tough to explain. You should get a copy of NEC 2008 and that would cover everything essentially. Specifics from vendors really just re-hash the NEC/NFPA rules and also include ANSI and MIL-Spec guidelines and compile the data into a manual.
I'll help you where I can.
You can start by looking on the web for mil-hdbk-419a
This will give you a starting point as it is MIL-Spec for comm sites. They require larger grounding and bonding conductors, which is not necessarily a bad thing (actually it is all relative to the type of soil and some specific variables about the soil) but it tends to be overkill for most instances (again, not bad but....$$$).
--
"No job is so important, and no service is so urgent that we cannot take the time to perform our work safely."
-- AT&T, Your World, Destroyed.
--Safety One Tower Rescue Certified
--LLigetfa:"Wimax is like teenage sex. Everyone talks about doing it." |
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battleop
join:2005-09-28
00000
| reply to shorthairedp
I think I found these pdfs somewhere on DSLR Forums.
One is AT&T's guide to "Grounding and Bonding Network Facilities - Design Fundamentals" the other is "Grounding and Bonding Requirements for Network Facilities" |
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AMD Phreak
Premium
join:2003-12-14
| reply to shorthairedp
I've never installed on a grain silo so I'd take the route below:
Install a small ground ring at the base of the silo. This ring should include three 5/8" x 8' CU clad steel. The rods shall be driven so the head is buried 30" below grade or below frost line, whichever is deeper. This is to ensure that the rod has complete contact with wet soil at all times of the year.
Space the rods so they are 16 feet apart from each other. Tie the rods together using #2 solid tinned CU wire using exothermic welds or UL listed high-compression connectors. Exothermic welds should be used to ensure 100% electrical and mechanical connections, plus they eliminate any chance of the joint rotting apart.
Loop them (rods) together so it is a closed ring. Also, bond a #2 solid tinned CU wire from this ring to the silo's electrical ground rod (located at the panel) to comply with NEC/NFPA. Bury this run a minimum of 18" or what local code states. It'd be best if this run was long to install 5/8" x 8' driven CU clad steel rods every 16 feet until you reach the utility rod, as this would further enhance your grounding system.
Install a downconductor from the top of the tower to the new halo. This conductor should be solid #2 tinned CU wire and it should be sleeved in non-metallic PVC pipe or flex to prevent incidental contact with the silo. Bond this conductor to the new halo with listed high-compression crimp or exotherm weld it. At the top of the downconductor (top of silo) put an appropriately sized tinned CU buss bar. Join the downconductor to this bar using exotherm weld (best) or listed high-compression crimp (2nd best). If you exotherm weld it, do this while its on the ground unless you can do it up top easily. Ensure this bar has insulators on it to keep it from being directly connected to the tower.
Join your antenna SPD's and antenna frames to this bar using #6 stranded green wire. Crimp fittings shall be listed high-compression crimps. Use only stainless hardware for the bar connection to ensure it doesn't rot apart. Also put some conductive grease between the crimped fitting and the bar (I use Penetrox) to keep the joint conductive.
This might not be the cheapest route but without knowing the details about silo installs this would be how I might approach it.
--
"No job is so important, and no service is so urgent that we cannot take the time to perform our work safely."
-- AT&T, Your World, Destroyed.
--Safety One Tower Rescue Certified
--LLigetfa:"Wimax is like teenage sex. Everyone talks about doing it." |
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gunther_01
Premium
join:2004-03-29
Saybrook, IL
| reply to shorthairedp
I might get flamed for this..But I did read once (but would have to dig it up) that a concrete structure ie grain silo. Is concidered at ground potential because of the nature of the concrete,rebar,and it's generally burried 20-30 feet deep. This isn't to say a "better" ground is needed for actual lightning suppresion. We have used on a couple structures, just the conduit for static discharge purposes. But I am also careful to only have "exactly, one" point of connection to any metal or conduit on a concrete grain structure. All of our equipment is metal but it's anchored to the structure independant of any of the structures already anchored or internal frame work.
I hate to say this as well, as it shows really how unreliable this is. I blew a few CM-9's before I found a good static discharge ground. But we also had multiple ground points then too. Knock on wood, all we ever see anymore are occasional hick-up's needing a manual reboot of the AP. And those only really happen during severe lightning/weather. It's hit and miss. But has been pretty solid otherwise. YMMV |
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Rhaas
Premium
join:2005-12-19
Bernie, MO
| said by gunther_01  :I might get flamed for this..But I did read once (but would have to dig it up) that a concrete structure ie grain silo. Is concidered at ground potential because of the nature of the concrete,rebar,and it's generally burried 20-30 feet deep. This isn't to say a "better" ground is needed for actual lightning suppresion. We have used on a couple structures, just the conduit for static discharge purposes. But I am also careful to only have "exactly, one" point of connection to any metal or conduit on a concrete grain structure. All of our equipment is metal but it's anchored to the structure independant of any of the structures already anchored or internal frame work. Bonding to the Steele that is encased in concrete is common practice and referred to as UFER grounding. I don't see it much here - the soil is easy to drive ground rods into and the water table is usually 15-30'. However, while I lived/worked in AZ this was very common in new home construction. |
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Splitpair
Premium
join:2000-07-29
Cow Towne | reply to battleop
I wonder who posted those to DSLR? 
Wayne |
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Splitpair
Premium
join:2000-07-29
Cow Towne
 ·T-Mobile US
| reply to shorthairedp
said by shorthairedp :How do I easily test the quality of ground, 150 feet in the air? You don't you will open the ground at the base and test from there.
Wayne
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If you cannot fix it with a buttset and some beanies you ain't a technician.
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AMD Phreak
Premium
join:2003-12-14
| reply to shorthairedp
You are correct in that a Ufer is a great ground. There are specifications for Ufer systems that mandate what exactly a Ufer is. The suggestion I listed was directly from my grounding manual that I must follow. That was one option for sites that are for rooftop or side mount antenna systems that need extra protection.
Again, I do not know how grain silos are constructed so I suggested this type of system. This system ensures that if there is a weakness in the silos electrical conductivity, lightning and static will still be shunted.
There are other types of systems like counterpoise radials and grids that also can be used to augment your system. Additionally, installing a chemically enhanced electrode can single handedly give you an extremely low potential ground system.
--
"No job is so important, and no service is so urgent that we cannot take the time to perform our work safely."
-- AT&T, Your World, Destroyed.
--Safety One Tower Rescue Certified
--LLigetfa:"Wimax is like teenage sex. Everyone talks about doing it." |
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gunther_01
Premium
join:2004-03-29
Saybrook, IL
| reply to Rhaas
said by Rhaas :said by gunther_01 :I might get flamed for this..But I did read once (but would have to dig it up) that a concrete structure ie grain silo. Is concidered at ground potential because of the nature of the concrete,rebar,and it's generally burried 20-30 feet deep. This isn't to say a "better" ground is needed for actual lightning suppresion. We have used on a couple structures, just the conduit for static discharge purposes. But I am also careful to only have "exactly, one" point of connection to any metal or conduit on a concrete grain structure. All of our equipment is metal but it's anchored to the structure independant of any of the structures already anchored or internal frame work. Bonding to the Steele that is encased in concrete is common practice and referred to as UFER grounding. I don't see it much here - the soil is easy to drive ground rods into and the water table is usually 15-30'. However, while I lived/worked in AZ this was very common in new home construction. I am aware of that type of ground. But I think at a grain elevator situation it's a hard one to do. These "structures" tend to be many, and far apart from the actual electrical ground of the electrical service. At least in my case where we had tried to bond to a hand rail that was installed and poured around during initial construction. We kept blowing cards. I think there was a ground loop from this situation.
I am NO electrician or grounding expert. Absolutely not... But I can tell you after working at grain elevators for 12 years. There is a lot of "stray" voltage that floats around them. These places tend to be fairly old that I have worked at. The electrical services from various motors, controls and additions seem to just "leak" a lot.
It's not right, a lot of the time. And I know it isn't at my elevator I manage. All except the really old ones I have worked at, are all fed with 3 phase 480volt . Have no dedicated ground system, short of the conduits that are screwed together all the way back to the service feeds and grounded there. It's just a tough place to find a single point of ground. As the whole structure is tied in to each other. It's also how the welders get away with 50' of ground line and hundreds of feet for the electrode. Clamp the ground at the metal where ever, and get to work  |
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