Site grounding
Posted: Sat Aug 23, 2014 6:24 pm
Preface or crib notes but read the entire post please wrote:I really wish WISPs would get more into proper grounding practices like cell carriers do which is where I learned it from.
1) Tower grounding system MUST be bonded to Electrical Service Ground else your Ethernet Cable is the bond. - VERY BAD
2) You can not rely on a steel tower being your ground run for several reasons so you NEED a dedicated "copper" ground cable run like #2 Green.
- A) Wire is made from copper because of its relatively low resistance, steel towers are a much higher resistance.
- B) Steel towers are usually multi parts bolted together and the connections are usually not good electrical connection.
- C) Surges from Static, ESD, or ground potential shifts will take the shortest less resistive path like your Ethernet cable unless you provide a dedicated ground path that is of less resistance and shorter run to ground than your Ethernet cable - THINK SERVICE LOOPS
3) Ground Bus Bars should be installed on insulators. The reason for this is you do not want to try and drain current from the whole tower just the steel in the area around your antenna/radios. This is why Busbars are on insulators even though a wire from them may go 10 feet and clamp to an antenna. You want as much current as possible to take the path of the tower so if there is a charge on the steel 20 feet below your bus bar most of that current will flow down the steel rather then travel up the steel to get on to your grounding system.
4) Service loops on your Ethernet are there primarily to increase the distance of the Ethernet cable to Earth ground raising the resistance of the Ethernet cable making it less attractive to surges. You can go through a lot the calculation to determining the resistance of the intended ground path run and then calculate your needed Ethernet cable length to insure the intended ground path is shorter and less resistant or I as a rule of thumb increase the Ethernet cable run with a service loop to be 10% longer than the intended grounding system run to Earth Ground.
5) You should use #6 Green to lug to every antenna mount, I use a lug and put it on the antenna clamshell bolts with conductive anti corrosion paste.
6) If your radio has a ground lug use it. I use #6 with a small lug for some radios but I also use smaller 10AWG & 12AWG for radios with small ground lugs.
7) Towers need multiple ground rods spaced apart all connected to the master ground busbar at the base of the tower. The ground rods "must" reach VIRGIN CLAY SUBSOIL as that is where the Earth Ground Plane is because clay contains most of the conductive minerals. If you are on a rocky site look into supplementing your ground rods with chemical ground kits.
8) Run #2 Tin if buried or #2 Green if above ground to your service ground rods and a ground busbar in/on your equipment box. Make sure to ground everything that has a ground lug in your box
9) Grounding systems need maintenance too. Every spring check your ground bus and connection to insure the connection are corrosion free and everything looks good.
I hate having to tell people their switch damage is not covered under warranty but I especially hate it when they know the damage was from a storm and claim it came DOA or something.
MHH wrote: Ground Loops Can Cause System Damage
Title: Ground Loops Can Cause System Damage
Keywords: Ground loops, Opto-Isolated, damage
Date: May 29, 1995
KDB: KDB-105
Revision: 0.00
Author: MHH
Distribution: External
Preamble:
“A ground loop is a current through a conductor between two two grounded points” as in two buildings connected by an RS-232/RS-485 data line.
The potentials are different and if the voltage is great enough … a current flows down the signal ground of the data cable … and your serial port is damaged.
When two devices carry a difference in ground potential, the potential will try to even itself out … in much the same way as water seeks its own level. It will travel through the the lines and connectors and overload the circuitry of both the high-potential and low-potential device.
** A lightning strike or electrical spike … is a sudden event causing damage … smoking chip/traces.
*** A ground loop is more insidious … and is a long term steady event that weakens the chip … and slow cooks the chips and they eventual fail … blackened tops and melted circuit boards.
Note: A surge protector does NOT guard against ground loops.
The best prevention for ground-loop problems is to use optical isolation on long data lines.
Many people ask me what I use for Ethernet surge protection and I have to say none. In the past I tried many Ethernet surge protection solutions and had mixed results but most often I had packet loss and Ethernet error issues. I used to lose radios all the time. However one day I sat down with a cellular site engineer and he explained that most of my problems were from ground potential differences. In the picture below you will notice that the tower is grounded, the electrical service is grounded, and the power company transformer is grounded.
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The problems above in order of importance:
The tower ground rod/system is separate from the service ground rod/system. If the tower grounding system and the electrical service ground system is separate the Ethernet cable running to your tower radios becomes a path for the ground potential differences. This often will cause your radio to lose it's Ethernet port yet the radio side continues to function normally. To bond these two ground systems either use #2 green for above ground or #2 tin for below ground.
The tower has only one ground rod. Personally I like to have 3 or better yet 4 ground rods for the tower as far away from each other as possible and in different directions like N,S,E & W and bond them all together. If driving the ground rods below the surface so as not to cause issues for lawn mowers I then trench between them so as to bond all of them together and always use CAD welding and #2 tin for below surface connections.
There is no direct ground wire run up the tower to a copper ground bus bar near my antennas with #2 green ground wire so I can ground each antenna to the ground bus with #6 green ground wire and lugs. Remember electrical current takes the path of less resistance and the steel tower is a higher resistance than your copper Ethernet cable. Now #2 green copper wire has a much less resistance than 24 gauge Ethernet.
The shelter Electrical Service only has 1 ground rod, you need at least 2 rods or even more as far apart from each other as possible then bond them together.
Lastly the power company is supposed to have an Earth ground rod at the base of every pole that has a transformer but often the crew is lazy and just throws a ground rod in the same hole as the pole when they set the pole. To make things worse most poles are only set in the ground 4-6 feet which means the ground rod never reached the clay sub-soil and thus is a poor ground. This can be a problem if you have a good grounding system on your site because now your site's grounding system may be the best path to ground for a large area around your site and attract stray voltages from the surrounding area. I do not condone this but I personally often go to the pole that has my transformer and drive in a second ground rod a few inches off the pole being careful not to hit any underground utilities like gas or water lines then I bond the two ground rods together providing a good ground path before entering my site.
Below is an example of how I would improve the site grounding system.
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I have not lost a single radio in the past 4 years on any tower and I do not use any Ethernet surge protection on my tower sites. I do have Trip-Lite inverter chargers that have electrical surge protection.
One should always remember that no matter how good a surge protector claims to be it is nothing but a placebo if you do not have a good ground system as what do you expect it to do with that surge if it has a poor path to ground?
Ethernet Transformers and what they do
Why Are Ethernet/RJ45 Sockets Magnetically Coupled?
Magnetic Coupling is used because of the problem that ethernet can support fairly long runs of 100 meters and as such equipment on different ends can be powered from differnt sub-panels within a building or even different buildings entirely with different ground potentials. This means there can be significant ground offset between ethernet nodes.
This is a problem with ground-referenced communication schemes, like RS-232.
When you do not BOND the tower ground to the Electrical service ground there is a ground potential difference.
When HEAVY rain occurs this can further change the ground potential difference between the two grounding systems. People often MISTAKE ground potential difference damage as Electrical storm damage. Most short duration heavy rain events occur in the spring and fall from rapid temperature variations which cause electrical storms but the real damage is from that couple of inches of rain in 15 minutes that does the real damage.
When you have a sudden heavy rain event the ground is often dry and causes the water to flood across the surface in sheets. When this sheet of water encounters a ground rod sticking up out of the ground it acts like a wic just like water follows your cable down the side of the building. This water is initially repelled by the dry earth around the ground rod and for a short duration this water acts as an insulator greatly decreasing the ground rods effectiveness, remember pure water is NOT a conductor and when the rain falls it is not Distilled Water but it normally does not have many conductive minerals in it and thus is a poor conductor. Once the ground absorbs the water it then leaches it's minerals into the water and it then begins to conduct based on your top soil content but for that short period the water was NON CONDUCTIVE and it only takes a microsecond of ground potential difference to fry your Ethernet Transformer.
Ethernet transformers can only protect against a finite amount of ground potential difference. They were designed primarily to deal with relatively small ground potential differences found in office buildings between electrical zones that all share a common Earth Ground System (set of ground rods bonded together).
If your tower ground system and your electrical ground system are not bonded the Ethernet cable becomes that bond, NOT GOOD!
To further make things worse early 10/100 wireless devices did not use POE Center Tap Ethernet Transformers but instead just hard wired the extra 2 pair as the DC feed to the remote device.
Now this in itself was not a bad idea until they did not use 1500V isolated power circuits which means that often the AC Earth Ground was bonded to the DC Negative circuite. This would then also be connected to the outer conductor of the SMA jumper which is also connected to your antenna which is in turn connected to the tower and thus the Tower Earth Ground System. This meant that the tower now had a direct connection to the radio DC negative that is now connected to the POE switch DC negative source.
This is yet another reason it is IMPORTANT to insure tower grounds are bonded to electrical service grounds.
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Why should ground rods be tight in the ground and penetrate VIRGIN CLAY 18" - GIGGITY
Most of your conductive minerals such as Iron Sulfate, Copper Sulfate, Copper Sulfide, settle down with gravity which is why the topsoil is more fertile as it contains the lighter minerals/elements used by vegetation. If your ground rod is loose this is an indication that water has eroded a cavity around the ground rod and when water flows into this cavity it will act as an insulator and GREATLY reduce the ground potential of the rod if not render it ineffective. A ground rod that penetrates the clay will form a watertight seal in the clay area and keep the ground rod productive. Often times they do massive earth moving in newer developments adding several feet of topsoil preventing a standard 8' ground rod from reaching clay if the contractor did not hit rock and just get lazy and cut it off. If I lose a radio Ethernet port at a subscriber I drive in a new 10' ground rod several feet away from the existing ground rod and bond them together with #6 copper and a couple acorns and clean up the existing connections....PROBLEM USUALLY NEVER HAPPENS AGAIN!
Most regions of the US have a topsoil predominantly of Silty Clay Lume which is a poor source of conductive minerals, you need to reach the CLAY SUBSOIL!
Service Loops, what are they really for
We all know to include an extra couple loops of wire at the radio, but do you really know why this was suggested by Engineers?
Well it sure was not to make sure you had extra wire in case you needed to re-crimp an end or move the radio! The real reason was to add distance between the devices hoping that there was a shorter path with less resistance such as properly running ground wire in a straight direct route. NEVER ADD EXTRA LENGTH TO GROUND WIRE! Adding those extra loops increased the distance and hopefully current would see the intended grounding system wires as a shorter path with less resistance and would leave your Ethernet cable alone! So always have a service loop of 3 or 4 loops, it could save your equipment!
What is a tell all indication that damage was from a ground potential difference and not an electrical surge.
The most common symptom of ground potential difference is when a radio still functions as a radio but the Ethernet port will no longer achieve a link or a degraded link. Another indication that a massive surge did not occur is the power supply still works. Trust me if you take damage from a lightening strike or massive surge more than just the board will get damage because for an electrical surge to reach your board it needs to go through the power supply....does your power supply still work? Trust me a near strike surge will render your power supply DEAD! Power supplies will be damaged from a massive surge but will NOT be damaged from most ground potential shifts unless they are MASSIVE!!
I have radios that have failed Ethernet ports and the radio still functions but they were installed on a roof of a house so how comes?
If the building has a POOR ground rod and during a sudden HEAVY rain event the ground rod can become rendered basically inert for a short duration. What people often forget is sudden downpours are often caused by an abrupt atmospheric temperature change which causes a NEGATIVE charge in the atmosphere. Also if you remember Newton's law that for every force or action there is always an equal opposite force or action. Well when there is a negative charge in the atmosphere there is often a positive charge on the "surface" of the Earth directly below the Negative charge which could envelope your ground rod that is momentarily inert from rapid water collection around it's shaft so for that short moment your best path to ground just might be your radio on the roof seeing path to a negative charge in the atmosphere.
So if you lose Ethernet ports at CPE installations check and or upgrade the ground rods.
And if you lose Ethernet ports on towers make sure you have your tower ground bonded to your service ground and make sure you have a better shorter path to ground than your Ethernet cables. I always add 1 or 2 new service ground rods to the existing rods any time I lose equipment at the tower.
It is important that ESD and Static charges at the Radio/Antenna have a shorter less resistant path to the grounding system through the intended grounding wire than through the Ethernet cable.
I always shake my head when people ground the base of a steel tower and think that is good. First off towers are usually multiple pieces of steel bolted together. Forget the fact that steel has a higher resistance value then copper but all those tower sections bolt together and every section joint is not a great electrical connection meaning they insert resistance.
From your radio/antenna you need a shorter heavier copper ground path with less resistance to Earth Ground than the Ethernet cables. This is another reason why you use a service loop in your Ethernet cables to insure the Ethernet cable path is longer than the ground wire path to Earth Ground.
If there is no dedicated copper wire for grounding from your radio/antenna to Earth Ground that is a shorter path and has less resistance than through the Ethernet cable then ESD and Static charge will follow your Ethernet cable.
If your tower ground potential is different than your Electrical service ground because they are not properly bonded then your Ethernet cable is the bond and the ground potential difference will constantly try to equalize through your Ethernet cable.
If your ground rods are not sufficient and in virgin clay or your ground potential is greater than 5 Ohms under normal conditions then rain events or ESD or Static discharges can overwhelm your grounding system.
Look the cellular guys put in those expensive grounding systems for a reason because with THOUSANDS of tower sites all over the place they would have towers dropping out all the time all over the place but they do not because they do GOOD grounding systems. Normally cellular sites take all but direct hits and keep on ticking.
You need good grounding. Look I have been preaching this for many years way back on the UBNT forums long before I ever started building switches. Do a search for my grounding posts over there and they preach the same things I am preaching today.
The only difference now is people expect me to replace or repair switches that get damaged from poor grounding for free.
We warranty our switches for defects or failures for 1 year but not from surges, ESD, Static discharges or user errors such as shorted cables or applying the wrong POE to an incompatible device.
Here is a good article:
https://www.lbagroup.com/products/light ... issipators
Grounding and other tower materials can be found at SitePro1
However #2 Green Ground Wire 6 AWG is cheaper at Home Depot
People should also review this post: viewtopic.php?f=17&t=1786&start=30#p13447
I hope you find this informative.