Grounding Do's Don'ts & Why Part 3

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by KF5LJW, Mar 19, 2012.

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  1. KV4QC

    KV4QC Ham Member QRZ Page

    Very interesting article. I have two small comments.

    The links are dead for your "models IB8RM or IBAR4" reference as it has been quite a while since your post.

    The Tripp-Lite "insurance is bogus in my EXPERIENCE!
    I was Manager of Electronic Engineering at a very large company where a Tripp-Lite surge filter/suppressor clearly failed and they refused to even hear about it.
    They arrogantly said "it was not possible for it to fail", and brushed us off!
    They would not even replace the $50 unit. So much for their $50,000 promise of insurance!
    I saved the unit and still have it!

    For 20+ years after that I would not buy anything from Tripp-Lite, but after looking for better products at reasonable prices I reluctantly bought more of their products.

    Even if their "insurance" was not honored, their products are good.

    KV4QC
     
  2. KV4QC

    KV4QC Ham Member QRZ Page

    Dereck,

    I just went back and read all three parts of your article.

    It is a very good service to the ham community and I found it to be very useful.

    Thank you,
    Mike
    KV4QC
     
  3. W2WDX

    W2WDX Ham Member QRZ Page

    Well that took some time to get through these three threads. Great information. I am happy to know it seems I am doing it properly. I never liked the term grounding, I always thought "common earth" was more betterer. Hehe.

    I think with the Bell Tower discussion I think both Dereck and Jim were on the same page, but just couldn't get past your respective perspectives. In the case of the Bell Towers it seemed they were initially using the tower foundations as the sole earth point, with no supplemental grounding. This forced all the energy through the encased steel, causing thermal expansion of the moisture in the concrete causing foundation degradation. Where Dereck was stating that both UFER and radial external grounding is commonly applied, something the Bell guys were saying to Jim was being added. I know that here in New York, buildings cannot use the foundation as the sole grounding as in an Ufer system. They must be supplemented with SGR or similar solutions to mitigate thermal expansion due to lighting strikes.

    Anyway, I live in 24 story hi-rise Co-Op in NYC and have all my grounding exothermically bonded to the building steel, both on the roof and in the shack. I was surprised how well this worked at reducing RX noise. This indicates to me proper grounding, since a side effect of proper grounding is low noise. The coaxial cable and all control & power cables and the conduit carrying these from the ninth floor shack to the roof are grounded at the entrance to the shack and at the roof. At the roof all the various antenna feeds go to a panel (which has remote antenna switching) to a block with commercial grade ADU's and is exo bonded via 4" solid copper strap to the structure. Same thing happens at the shack end before it enters my unit where the structural bond is in the stairwell where the conduit goes up to the roof. The same type of panel and ADU's bonded to the building steel. There is a oawg solid wire coming from the same ground point in the stairwell into the apartment, leading to the equipment ground bar and another to the main AC panel for my unit. The big reduction in noise occurred when the last bond between the AC mains panel and the shack ground was added. It is a 0awg stranded copper wire leading from the panel where the ADU's are in the stairwell with the exo-bond, back to the AC panel inside the apartment. The shack has a copper ground bar attached to that same ground point running behind the full length of the equipment tables.

    My only concern is whether the AC grounding is proper in the other units on my electrical leg feed. I hope my ground isn't the only quality safety ground. There is no way to tell, short of inspecting the entire electrical system of the building. But the Bronx borough of NYC has always had codes that exceed NEC, which is where "BX cable" came from ... "BX" meaning Bronx. The Bronx code was also the first to ban the use of aluminum wire. This was from a time before the NEC existed.
     
    Last edited: Nov 15, 2017 at 3:05 AM
  4. KF5LJW

    KF5LJW Ham Member QRZ Page

    Installed many a telephone offices in NYC, Newark, Chicago, and many more cities. All are high-rise buildings. In any High Rise building. Built and wrote the book on how to properly bond in high-rise buildings. All of them use the Structural Steel and Cold Water Pipe ground. Nothing more is needed and going beyond that has no benefits because no improvement can be made. Stop and think about that for a minute. Then ask yourself what could you possible do to improve on a massive chunk of concrete and rebar the size of a city block 50 feet thick, with 40 stories of weight bearing down. The surface are of that conductor is massive. I have tested several high rise building Earth Resistance, not a single one of them measure greater than 1-Ohm 3 of the 4 test was invalid because the Impedance was too low. There is nothing you possible could do to improve on perfection. Only thing you can do as you wisely have is use the Building Steel as your Ground Electrode. Not one single Ham has a better earth ground than you do.

    Where you bond to building steel is extremely important. Real simple if you operate out of the 25th floor of a 50 story building, bond to building steel on the 25th floor. Go above or below, and you risk electrocution and fire when LIGHTNING strikes the building. In fact about 20 years ago I sat on a IEEE Committee per review investigation the grounding and power that was designed by the PE Engineer. A Telco installed a Switch up on say floor 25 of a 50 story building. Using Telco mentality in the design, this engineer attempted to use a Isolated Single Point Ground System used in Telco and data center. So he ran dual 750 MCM cables all the way to the lowest basement to bond them the AC Service Ground. The 2 x 750 MCM conductors were insulated. Well lightning struck that building seriously injuring a Telco technician, and turned $20,000,000 into a brick.

    So what was wrong? Well when a high rise building is struck by lightning, the building becomes a voltage divider along length of its height. So say lightning strikes and the point Voltage at the strike is say 40,000 volts on the 50th floor. If you were to measure voltage on each floor building steal, it would decrease the closer you get to DIRT. At the 25th floor voltage would be 20,000 volts being half way down. Then in the Basement voltage is ZERO. Figure out what happened. The idiot engineer ran 2 x 750 MCM cables all the way down to the basement to connect to building steel. So when lightning struck the building, The electrical system remained at ZERO Volts because it is referenced 225 stories below, while the 25th floor was at 20,000 volts. There were multiple Flash Overs from the electrical to building steel. One of those paths was through the technician. Conclusion of the investigation. Bond to building steel where your equipment is located as code requires. If this had been done, there would have been no problem. The Ground Plane voltage would have floated up to 20,000 volts, and then sink back to 0 volts. Everything would be at the same Voltage at all times. Both Building Steel and Electrical remained at 0 volt potential difference.

    Lastly in a high rise, all lightning strikes use the building steel as the down conductor and enters earth through its massive slab of concrete. Does not matter if it is a high rise building or radio tower. It is just the nature of the design when you use a huge steel reinforced concrete foundation with anchor bolts and set a tower or building on it. It is impossible for you to divert any significant amount lightning current away from the cason. That kind of structure earth resistance is a lot lower than any thing you can add on. You can bleed off or Shunt some current away from the cason, but you cannot stop the current. Stop and thin about it. Say the Tower Cason aka Ufer is 1-Ohm. You would have to bury enough copper to get down to 1-Ohm to be of any significant value to shunt away just 1/2 the current. You are talking a load of many spent that does not buy you anything meaningful. You are required to bond to the tower as part of the Ground Electrode System, and you should because it is the best electrode in your system.
     
    Last edited: Nov 15, 2017 at 5:08 AM
    KD4MOJ likes this.
  5. WD0BCT

    WD0BCT Premium Subscriber QRZ Page

    The National Electric Code was originally published in 1897. I got to see a copy of it. It was only a couple of pages!
    I'm not really sure when aluminum conductors were first manufactured.
    Aluminum is actually still in use. The problem with aluminum terminations getting hot and causing fires was due to two things that have been corrected today....first the aluminum alloy was too soft and flowed easily...and secondly the terminations were designed for copper conductor alloys. Although both of those issues have been addressed today, the stigma of hot aluminum terminations still exists and many still do not allow aluminum conductors in there designs.
    With copper and aluminum prices changes aluminum makes a comeback when the price is right and fades when it loses a large price advantage.
     
  6. W2WDX

    W2WDX Ham Member QRZ Page

    I didn't know that about the NEC being first published in 1897. Ya learn something new everyday.

    On aluminum wire, I wasn't clear. Older aluminum alloys are banned. There are newer alloys that are specified for specific uses in the NEC as of 1981 & 1987, and only if they are of this new alloy (AA8000? I think). The biggest problem was with galvanic problems leading to corrosion which creates resistance (heat).

    So I'm trying to wrap my head around this. I understand the "voltage divider" you describe across the height of the building. So the question is (and I should know the answer) does this mean you do NOT ground at the entry point on the roof? Is the building acting as a step potential like the earth can? That seems counter-intuitive. Given the low impedance and low resistance of the building steel, not to mention the consistency of those parameters over its distance, would not the voltage be normalized? (Yes I do realize building steel is not a perfect conductor).

    So you say only ground at the equipment level. So the antenna entry point at the building roof should float, and not until it reaches the lower floor be grounded at the lower floor? That doesn't sound right. Or am I just getting this wrong. I have ADU's at the roof level grounded to the building steel outside there, and I have additional ADU's just outside my apartment where the cable enters the apartment on the ninth floor. My station and AC panel is grounded at the ninth floor level bonded to the same ground point at the ninth floor ADU panel.

    It seems to me the relative potential at the roof is ~zero and at the lower floor the relative potential is also ~zero. The relationship is the location itself; roof or lower floor. If the potential across the building is different in your voltage divider example, does not this require ground at both relative potentials. Grounding only at the equipment would create a potential difference between the antenna and the equipment relative to each other, right?
     
    Last edited: Nov 15, 2017 at 11:20 PM
  7. KF5LJW

    KF5LJW Ham Member QRZ Page

    No Sir you bond coax sheaths/shields to building steel on the roof. Same as you would do if it were a Tower. Bond sheaths/Shields to building steel as you work down periodically like every 2 or 3 floors. Once you get to the Equipment Room you make your final bond with a Antenna Discharge Arrestor. So when and if lightning strikes, by the time it reaches say the 25th floor, with the hardlines being bonded multiple times drains or Shunts off to building steel keeping fault current to acceptable levels. With everything referenced to building steel on the same floor, lightning currents cannot not flow through the equipment because there is no ground return path or to be technical correc; no voltage potential difference . The only path to dirt is via building steel.

    Perhaps it might help if you think of building steel being an direct access point to the facility Ground Electrode System. Another way is say your home with a Ground Ring that gives you access to the Ground Electrode System from any point you enter/exit.

    Another point you noted, if done correctly makes for one heck of a QUITE SYSTEM. Why? Because you have created a Noise Free Reference point for everything. You have established a Ground Plane on the 25th floor. The best way to screw that up is run a ground conductor down to the basement. Now your reference point is at dirt level, and your 25th floor is at a different potential. All that building steel acts like an antenna, couple that with normal power current flowing through building steel give you all kinds of noise to deal with. Or just bond to guilding steel as code and best practices calls for, all that goes away.
     
    Last edited: Nov 16, 2017 at 3:48 AM

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