Site grounding

This is my personal thread to share practices that have served my WISP well
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gripper
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Re: Site grounding

Thu Jul 14, 2016 12:34 pm

sirhc wrote:
So you're saying the tower is 50' away from your equipment?

Probably more like 30' horizontally.

This is BAD as the building where the equipment is probably has a DIFFERENT Earth Ground.

They are actually bonded, probably #2

Grounding radios to towers is NOT a grounding system. Steel is a much higher resistance than copper so any stray current, static charge, or ESD charge will take the nice copper Ethernet cable instead. Yes there should be a MAIN ground bus on insulators at the base of the tower that is connected to all the ground rods or halo system for the tower. As well the tower should be connected to the ground rods as well but but to your bus which is insulated. You always insulate your grounding system except where it bonds to the antennas as you do not want to drain the tower in the middle of charge but rather hope that charge follows the steel down as much as possible so as not to overwhelm your ground path. You only want to drain the steel at your antennas. You're hoping charge in the middle will go down the tower instead of up and then into your ground wire as the tower legs are also bonded to the ground rods.

Now I get it--two independent ground paths--one for the radios/antennas and one for the tower steel. I suppose digging down and tying in the antenna ground path as low as possible to the halo and rods (and enhancement material, etc.) is preferable?

There should be a BOND wire between the tower ground system from this main bus to the service ground rods and a ground bus in your cabinet but since this is 50' away it should almost be #1 gauge wire which is 1" thick.

See above


There should be a #2 green running up the tower to an insulated ground bus near your antennas and a #6 from that bus to each antenna/radio.

If the radios are spaced over 30 or 40 vertical feet, where to locate the (single?) insulated ground bus? High, low, mid-range?

You want to make sure you have ample Ethernet Service loops so your Ethernet path is at least 10% longer than the intended ground path.

If they are run the additional 40-50ft to the cabinet (as opposed to the existing LA's at the base of the tower) they're a lot longer. And why the 10% rule of thumb--is this empirical in any way, i.e. corresponds to the conductivity difference between copper and steel?

You need understand that ground potential differences is just as dangerous to your equipment as ESD and Static discharges.


Follow the guidelines in these posts (Read these posts several times):
http://forum.netonix.com/viewtopic.php?f=30&t=1816
http://forum.netonix.com/viewtopic.php?f=30&t=188
http://forum.netonix.com/viewtopic.php?f=30&t=1429
http://forum.netonix.com/viewtopic.php? ... =30#p13447

The idea is that all equipment is within 5 ohms of each other as far as ground potential and no matter where there is stray voltage or CURRENT that the intended path is shorter and less resistive than the Ethernet cables.


I don't suppose testing ground potential difference under ordinary conditions means that it would look like the same under the conditions of a nearby lightning strike. You just hope your grounding system is up to the task of distributing charge when something like that happens....

Thank you for your time and passion as the Grounding Guru and Evangelist.

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sirhc
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Re: Site grounding

Thu Jul 14, 2016 1:37 pm

Answers in RED BOLD below:

So you're saying the tower is 50' away from your equipment?
Probably more like 30' horizontally.
Thats should be OK.

This is BAD as the building where the equipment is probably has a DIFFERENT Earth Ground.
They are actually bonded, probably #2
#2 for 30' is OK

Grounding radios to towers is NOT a grounding system. Steel is a much higher resistance than copper so any stray current, static charge, or ESD charge will take the nice copper Ethernet cable instead. Yes there should be a MAIN ground bus on insulators at the base of the tower that is connected to all the ground rods or halo system for the tower. As well the tower should be connected to the ground rods as well but but to your bus which is insulated. You always insulate your grounding system except where it bonds to the antennas as you do not want to drain the tower in the middle of charge but rather hope that charge follows the steel down as much as possible so as not to overwhelm your ground path. You only want to drain the steel at your antennas. You're hoping charge in the middle will go down the tower instead of up and then into your ground wire as the tower legs are also bonded to the ground rods.

Now I get it--two independent ground paths--one for the radios/antennas and one for the tower steel.
Yes, sort of. The tower itself uses itself for primary ground path which is horrible as described already being steel and sections bolted together. The radios and the part of the steel tower around them has a ground lug to the aerial isolated ground bus.

I suppose digging down and tying in the antenna ground path as low as possible to the halo and rods (and enhancement material, etc.) is preferable?
Well there should be a PRIMARY ISOLATED TOWER GROUND BUS at the base of the tower that connects to the Halo/rods and is where the #2 Green running up the tower and the bond over to the service grounds and equipment box connect to.

There should be a #2 green running up the tower to an insulated ground bus near your antennas and a #6 from that bus to each antenna/radio.

If the radios are spaced over 30 or 40 vertical feet, where to locate the (single?) insulated ground bus? High, low, mid-range?
I would center it. Remember that ground wires should NEVER loop and always swooping curves and it you pretend they are pipes water put in the top will all flow empty to the bottom.

You want to make sure you have ample Ethernet Service loops so your Ethernet path is at least 10% longer than the intended ground path.

If they are run the additional 40-50ft to the cabinet (as opposed to the existing LA's at the base of the tower) they're a lot longer. And why the 10% rule of thumb--is this empirical in any way, i.e. corresponds to the conductivity difference between copper and steel?

Well actually the "proper" way is to calculate the resistance and capacity of your ground run taking into account insertion loss for connectors and such from every radio to ground then calculate the resistance of your Ethernet run and make sure the Ethernet is run is at least so much higher and longer than the intended ground path and the capacity of the ground paths is to be based on many factors. SO I JUST CAME UP WITH A RED NECK CHEAT AND FOUND THAT 10% LONGER ETHERNET RUN IS SUFFICIENT MOST TIMES.

You need understand that ground potential differences is just as dangerous to your equipment as ESD and Static discharges.

Follow the guidelines in these posts (Read these posts several times):
viewtopic.php?f=30&t=1816
viewtopic.php?f=30&t=188
viewtopic.php?f=30&t=1429
viewtopic.php?f=17&t=1786&start=30#p13447

The idea is that all equipment is within 5 ohms of each other as far as ground potential and no matter where there is stray voltage or CURRENT that the intended path is shorter and less resistive than the Ethernet cables.

I don't suppose testing ground potential difference under ordinary conditions means that it would look like the same under the conditions of a nearby lightning strike. You just hope your grounding system is up to the task of distributing charge when something like that happens....

Well the professional do test and yes it is not a guarantee that the system will hold up under all adverse conditions such as near strikes, Static load, and rain/water isolating ground rods that are not properly set in clay.

Thank you for your time and passion as the Grounding Guru and Evangelist.
My pleasure, the only frustrating point is many times it is an uphill battle getting people to realize the importance of proper grounding. Most people think ground is ground and I am quack. :headb:

So last night I was up late last night in the garage talking to my mother-in-law and a NASTY storm rolled through and today when we came into RF Armor / Netonix facility we found that our 52' LCD TV on the the lunch room wall was fried from the storm..... :tounge:

MY 9 YEAR OLD SON DAVID IS REALLY UPSET AS HE IS STUCK HERE DURING THE DAY WITH NO TV TODAY. :pissed:
Long story short we lost ZERO radios on our towers or customers last night!
:hurray:
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Re: Site grounding

Fri Nov 04, 2016 11:12 am

One thing is driving me crazy reading this thread.

Copper ethernet wire is not (generally) lower resistance than a steel tower. Resistance is a product of resistivity and dimensions of the conductor. A narrow gauge ethernet cable is going to have a much higher resistance than a tower or pole, steel or aluminum, unless that tower does not have contiguous metal all the way to the ground (i.e. corrosion, bad joints, etc).

This should be quite easy to understand, because you know that 2AWG wire has much less resistance than 22AWG wire.

https://en.wikipedia.org/wiki/Electrica ... nductivity

By the way, this page does a good job of explaining common tower grounding problems.
http://www.w8ji.com/station_ground.htm

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Re: Site grounding

Fri Nov 04, 2016 11:37 am

brock wrote:One thing is driving me crazy reading this thread.

Copper ethernet wire is not (generally) lower resistance than a steel tower. Resistance is a product of resistivity and dimensions of the conductor. A narrow gauge ethernet cable is going to have a much higher resistance than a tower or pole, steel or aluminum, unless that tower does not have contiguous metal all the way to the ground (i.e. corrosion, bad joints, etc).

This should be quite easy to understand, because you know that 2AWG wire has much less resistance than 22AWG wire.

https://en.wikipedia.org/wiki/Electrica ... nductivity

By the way, this page does a good job of explaining common tower grounding problems.
http://www.w8ji.com/station_ground.htm


1) Yes Steel has a higher resistance than copper, even if the tower was 1 contiguous piece.

2) Most towers are made up from many sections and those joints are coated with paint or galvanization and they are corroded and this adds insertion loss or resistance.

3) The resistance of a a thin piece of copper is much less than a think piece of steel until the capacity of the copper is reached and it starts to heat up raising its resistance so then it is possible that the steel could become less resistant than the copper wire as it is pushing too much current and heated up but by this time the damage is done.

If their is a charge on the tower at your antenna the first place that charge will go to get to ground without a dedicated copper ground path which is lower than the Ethernet Cable is your Ethernet Cable if you are relying on the steel as your primary path to ground for ESD and Static . Yes as the Ethernet Cable capacity is reached which it will quickly then its resistance value will increase and eventually the steel tower will look more attractive but by then the damage is done.

But most damage I see is ground current traveling between the electrical service ground and the tower ground because they are not properly bonded. Look your ground rods have a limited capacity to discharge excess current that many devices such as electric motors or surge suppressor clamp to Earth Ground so the more current that is going to the ground rod the higher the resistance to ground it becomes. Now if the ground rod is not sufficiently penetrating virgin clay which is where the majority of the conductive mineral are such as iron sulfate, potassium. calcium, and so on which is why clay is so much heavier than top soil which is low in conductive mineral and you have a sudden rain down poor the water wicks down the ground rod like water down a cable and floats or isolates the rod dramatically as H2O itself is an insulator reducing its connection/capacity and raising its resistance to the ground plain until the mineral leach out of the soil and mix with the water restoring the rods connection to Earth Ground. But during this short period of time the resistance and capacity to Earth ground get poor and suddenly all that excess current on your Earth Ground wires in your building see the Earth Ground of the tower as a much lower resistance and current shoots up the wire to get to the tower ground and POP.

It can also happen in the other direction if the tower grounds suck and the service grounds are better and the tower gets a charge from ESD or Static and especially if you do not have a dedicate ground path that is lower resistance and sufficient capacity to carry that charge away from your Ethernet cable.

Look, the Cellular industry has many very smart engineers working for them and they have been in the industry for many many years so there is a reason they bond all steel together on a site. They also run dedicated heavy gauge copper wire up the tower and do not reply on the steel as their ground path. They also make sure that their electrical service ground rods are bonded to the tower ground rods so that there is only ONE ground potential on the site.

When a cellular company puts up a site Earth ground testing is always preformed and they will not pass any site that has more than 5 Ohms between any 2 metal points on the site and to Earth Ground. 2 of my tower guys (Eldon and Joel) came from the cellular industry and used to do nothing but cell sites. They are the reason I now do grounding the way I do it, just like the cellular industry.

YOU SHOULD NEVER RELY ON A STEEL TOWER OR WATER TANK AS YOUR PATH TO EARTH GROUND.

But hey do your grounding are you see best, it is your tower and your equipment.
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Re: Site grounding

Mon Nov 07, 2016 7:25 pm

It's plain physics. I did say, corrosion and bad joints could compromise it, but there's no way in hell a tiny wire made of copper has less resistance than a huge tower made of steel (provided there are no bad joints). Copper has a lower resistivity than steel, much lower (just under 10x lower), but resistance is a product of resistivity, cross-sectional area, and length.

I'm not advocating grounding to the tower. However, "steel has a higher resistance than copper" is not a good reason not to, because it's nonsense absent the other variables.
Last edited by brock on Mon Nov 07, 2016 7:52 pm, edited 1 time in total.

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Re: Site grounding

Mon Nov 07, 2016 7:27 pm

sirhc wrote:
1) Yes Steel has a higher resistance than copper, even if the tower was 1 contiguous piece.


Resistance = resistivity * ( length / area) (Pouillet's law)


So, for equivalent resistance we can say:

resistivity(copper) * (length(copper) / area(copper)) = resistivity(steel) * (length(steel) / area(steel))

Since we are assuming the same length of metal from the grounded radio to the ground whether through tower or ethernet wire, length(copper) = length(steel), and we can divide through by that to remove it.

resistivity(copper) / area(copper) = resistivity(steel) / area(steel)

Divide through by resistivity(steel):

resistivity(copper)/(resistivity(steel)*area(copper)) = 1/area(steel)

Invert:

area(steel) = (resistivity(steel)/resistivity(copper))*area(copper)

So if CAT6 is 23 gauge, that's 0.258 mm^2 (per https://en.wikipedia.org/wiki/American_wire_gauge)


Multiply by 8 wires, that's 2.064. Call it 2 mm^2.

Now from this: https://en.wikipedia.org/wiki/Electrica ... nductivity

resistivity(copper) = 1.68
×
10^-8 ohm-meters

resistivity(steel) = 1.43
×
10^-7 ohm-meters (1010 carbon steel)


Filling in the variables, we get:

area(steel) = (1.43e-7 / 1.68e-8) * 2 mm^2 = 8.5 * 2mm^2 = 17 mm^2.

If the (one piece, as you said) tower has a cross-sectional area of greater than 17mm^2, it has less resistance than an Ethernet cable.

If you bear in mind the voltage divider issue discussed above it becomes apparent why using a grounding cable is still a good idea even if you have a massive contiguous tower, because you want to shunt as much current away from the radios as possible, and the lower the resistance of every other path to ground the better. Much easier to do that with heavy copper wire.

#2 copper, for example, has a cross-sectional area of 33.6 mm^2. You'd have to have 285.6 mm^2 of steel to match that, which is about 17mm x 17mm.

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Re: Site grounding

Mon Mar 27, 2017 11:56 pm

Thank you for all of this information! I'm pretty nervous for the next storm because I am doing something different than I have in the past and my setup is a little different for now. If I use an isolation transformer, then run the isolated AC to a DC power converter, run the DC up the tower but no Ethernet (the networking equipment is up the tower), should I bond the negative lead from the DC power converter to the grounding system?

Update - Just a little more information. My Networking equipment box is on the tower (about 450 feet up) but by (previous) design it is insulated from the tower - nothing us grounded in the box and essentially it is rubber lined. I understand now that the negative power is grounded to the tower through some of the radio units. All antenna mounts are now grounded with a separate copper run down the tower. For the time being it is #6 - I have #2 on the way. I tied my #6 copper to the tower grounding system and ran #2 from it to the building ground system, which is tied to the site power with (unfortunately) maybe #6 or smaller.

My Ethernet cables on the tower are basically in metal conduit. They are shielded but I did not use metal connectors, so the only ground point up here is the power to the radio units through the antenna mounts (and the new copper cable run).

So from the bonded "tower - myNew#6 - ACservice" ground to the negative output of my DC power supply, I have 3 volts. It makes a small spark when I hook them together. I am afraid that if I bond the grounding systems to the output of my power supply I just gave a path to ground through my power cable that I didn't have before.

I am going to ground the control box and the components as soon as I can, but I still would question grounding the negative power cable on the ground. Any advise would be appreciated. Thank you!!

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