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  • #16
    Originally posted by Barba View Post
    I don't live in a rural aerea, but 5 ohms is required by law when DC voltage is above 80 Vdc.
    The inverter instructions is talking about 2 ohms.
    I ask the company and they analyse the soil before doing the job.based on the soil type they will operate accordingly.
    The contract states 2 ohms in achieved after 2 weeks and it is guaranteed for 5 years.
    I don't know the price yet as it all depends on the soil.
    Complete stupidity. Not you, your codes. More like a SCAM. Ground does NOTHING. At 80 volts, and 2 Ohm Fault Return path could not operate a 30 amp breaker. With a 2-Ohm return path would make any load great than 5 amps useless because the voltage loss is to severe. Think about it. You supply 80 volts at one end of the circuit and only get 60 volts out the other side. Complete stupidity.
    MSEE, PE

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    • #17
      It is possible to get that low of resistance but it will be expensive. A friend of mine works for the local telco and they get their grounds to under 5 ohms at very great expense. They use a copper grid using class 2 lightning conductor (4/0 size), in a net pattern with 6' spacing all at least 30" underground - yes, it is a ring electrode 250.52(A)(4). We are talking about at least 1/2 mile of this stuff in this pattern. Every cross is exothermic welded and everything is encased in GEM (ground enhancement material) it is sort of like a cement. This is all under their storage yard next to the main building.

      Crazy expensive. But they get their 5 ohms and due to the size and GEM it is that year round. They are required by code to be 5 ohms or less being a commercial telecommunication site.

      Another friend works for Verizon and does the cell tower servicing throughout the greater Yosemite area. They also have to get their cell sites by code to 5 ohms or less and they do the same sort of thing - massive grid underground, GEM, etc. Can be insanely expensive when they put up a new site - but hey - Verizon can afford it.
      Last edited by tyab; 11-11-2016, 07:07 PM.

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      • #18
        Originally posted by tyab View Post
        Crazy expensive. But they get their 5 ohms and due to the size and GEM it is that year round. They are required by code to be 5 ohms or less being a commercial telecommunication site.
        There is absolutely no Code Requirement what so ever for any Telecom to have 5-Ohms or less. NONE. I know because I have built hundreds of Telephone offices, data centers, cell towers, banks, 911 Call Centers, you name it professional for over 35 years. I even wrote standards for Verizon when I was at Worldcom. I also sat on Code Panel 9 of NFPA NEC as a contributor to article 250.

        True you might see some Telecoms require in theeeeir building specs to have 5-ohms or less, but there is not a single engineer that could explain why or justify that number. They have no clue and are reading specs from 60 years ago. There is no reason what soever to state a specific requirement. Notta nothing.As for electrical codes there no difference if the service is for a 50-amp single phase service to a mobile home or 100,000 ft^2 telecom facility, the code requirements are the exact same. Drive two rods and collect a check. Why because there no reason to meet any specific target to meet. Ground is forbidden to be used as a Conductor in NEC applications. End of story.

        So where does 5-Ohms come from in Telecom? Well it comes from the days of when city water systems were metallic pipes from plant to home, and telephone companies used PARTY LINES, the Telco used earth as a conductor for the Ringer Circuit. Saved the Telcos millions of dollars. In that day required your home or biz to have 25 ohms or less. Telco party lines applied Ring Voltage in 3-Modes of Tip to Ring (the pair used today for both voice and ring voltage). Tip to Ground, and Ring to Ground. That way you could have at least 3 houses on the same circuit so when you called them, only their phone would ring. In those days obtaining 25, 5, or even 1 Ohm was simple, use the WATER PIPE every house and biz has. Even electric utilities used the Water Pipes for Earth Ground. At worse case your ground resistance to the Telco was no more than 30 ohms. That is less than the two 20,000 foot conductors used for tip and ring and it was FREE to use.

        Problem is a lot of water utility, electric utility, plumbers, and home owners were killed and injured by using earth as a conductor and is forbidden today. Telephone companies no longer use party lines or frequency selective ringers. Ring Voltage is applied to Tip and Ring conductors and ground has ZERO use or function.

        Yes some telephone companies still require 5-Ohms in building specs out of ignorance like the manufactures. Old Standards die hard. Today most have upgraded their standards, but have dropped the 5-Ohm requirement. They are still going to get that or close because they do have requirments that exceed the code minimums to control Lightning and Transient Voltage Surges from Outside Plant cabling and Radio Towers, but no specific ohm requirement is needed to be met.

        Smart Telcos and operators unless there is a tower involved only use Three Ground Electrode required by code minimums. A Concrete Encased Electrode which will outperform anything you can bury and cost almost nothing to implement other then the EC bonding to the rebar before they pore concrete to make a UFER Ground, a connection to the useless plastic water pipe, and the building Structural Steel member near the AC Service entrance.

        Stop and think about this you have a 200 AMP service to most homes, Lest say you have a 2-Ohm Ground. So you are working on your breaker panel and come in contact with one of the 200-Amp Phases and that expensive 100 tons copper rod you buried GROUND to protect your dumb ass. Your 200 amps breaker is now passing 120 volts / 2-Ohms = 60 amps through your smoking dumb ass body burning you to a crisp. Please tell me how 60 Amps of current flowing through a 200 amp breaker and you is going to cause the breaker to operate and save your dumb ass? Will not do a dang thing, your dumb ass is dead. FWIW I am not directing that at anyone, just getting your attention and make you laugh. This means you.

        Today no water pipe is continuous. Water companies kicked the Telco and electric utility off their lines a long time ago. They did it at your water meter with a Dielectric bushing to isolate you from them electrically. Gas company never allowed any connection. They knew better.
        Last edited by Sunking; 11-11-2016, 08:42 PM.
        MSEE, PE

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        • #19
          What's good in ohms to ground my inverter?

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          • #20
            Originally posted by Barba View Post
            What's good in ohms to ground my inverter?
            There is no particular value that is "good" in the sense that it is the maximum resistance recommended.
            You do not need to ground it at all, although for some fluorescent light loads it may not work as well on an ungrounded system.
            SunnyBoy 3000 US, 18 BP Solar 175B panels.

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            • #21
              Sunking

              I asked my SierraTel friend why they have the 5ohm requirement and today he got back to me this afternoon that they "think" it is a IEEE requirement but not an NEC requirement. I guess the my question to him started a long discussion with the engineers on why exactly they go through all this effort - and it seems that most share your thoughts but they do it because they have always done it that way. One of the engineers stated that some of the equipment they use has it as part of their listing requirement but he could not quote what equipment it was. He told me that they are looking into it and he will get back to me when he has more info. Sounds like your summary of the issue is correct - and this may be similar to the issue of CNC machines requiring a ground rod for no other reason than it was used in the past. I sent a message to my Verizon friend about this same subject but have not heard back from him. The SierraTel guy also said they put in the large GRE (ground ring electrode) for lightning but that does not have a ohm requirement. Makes them all wonder why they go through all this expense to hit that 5 number.

              Thanks for the history lesson on it - sure makes sense from a party line point of view.

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              • #22
                Originally posted by tyab View Post
                Sunking

                I asked my SierraTel friend why they have the 5ohm requirement and today he got back to me this afternoon that they "think" it is a IEEE requirement but not an NEC requirement. I guess the my question to him started a long discussion with the engineers on why exactly they go through all this effort - and it seems that most share your thoughts but they do it because they have always done it that way.
                Duh! Bottom line is they have no clue why. All they know is some requirement from the Civil War telegraph lines.


                Originally posted by tyab View Post
                One of the engineers stated that some of the equipment they use has it as part of their listing requirement but he could not quote what equipment it was. He told me that they are looking into it and he will get back to me when he has more info. Sounds like your summary of the issue is correct - and this may be similar to the issue of CNC machines requiring a ground rod for no other reason than it was used in the past. I sent a message to my Verizon friend about this same subject but have not heard back from him. The SierraTel guy also said they put in the large GRE (ground ring electrode) for lightning but that does not have a ohm requirement. Makes them all wonder why they go through all this expense to hit that 5 number.

                Thanks for the history lesson on it - sure makes sense from a party line point of view.
                OK there is no LISTING REQUIREMENT or any reason to hit 5-Ohms. Stop and think about it. If you have a typical 480/277 1200 Amp service with a 5-Ohm earth ground please tel me what the fault current would be?

                277 volts / 5 ohms = 56 amps. So please tell me what 55 amps on a 1200 breaker does? Absolutely nothing except kill you if you are the fault with 55 amps smoking your body with 15 Kw of power boiling your blood and searing your flesh.

                Do not get me started with CNC machines needing a isolated ground rod. Not only is that extremely dangerous but can wreck havac on the electrical system common mode noise making the CNC machine useless. Complete stupidity on the manufactures part and violate all electrical codes. Every Inspector would fail such an installation.

                FWIW I am the contributing Author to IEEE Emerald and Green Books. I also sat on NEC Code Panel 9 which writes the codes for article 250 and a hand full of other codes. The idiots at Verizon stil use th eGrounding practices I wrote in 1999. Verizon does not have engineers, they have over paid purchase agents. Verizon like Ma Bell and ATT fired the real enginners back in the 80's, 90's and early 2000. I went in 2003.

                OK do not come away with that a telecom does not need a good ground protection system because they do. But a Ground Electrode System is to protect the facility from what is OUTSIDE, not what is INSIDE. The whole point is to keep Lightning and POCO faults from entering the building and mitigation of signal reference systems.

                Now here is another kernel of facts to consider. Most Telco require a 750 MCM Ground Electrode Conductor to a 5-Ohm ground. Now here is the stupidity and ignorance. The 5-Ohm reference is a POWER FREQUENCY impedance, not resistance of 0 to 300 Hz. Fine and dandy, 5 Ohms is astronomically way to high to operate any safety equipment. No where is the Ignorance. Lightning is not Power Frequencies. It is a current impulse with extremely fast rise times. Most of the energy is contained in an equivalent 10 Mhz.

                So riddle me this. What is the Impedance of a 10-foot long 750 MCM cable or 2/0 Cable @ 10 Mhz? Got an aswer? Makes no difference if it is 2/0 or 750 MCM as both have roughly the same impedance of 2 K Ohms. Another Riddle. What is the Impedance of 5 Ohms in series with 2000 Ohms Inductive. Was your answer 2000 Ohms? Change 5 Ohms to say 25 ohms, you stil have the same useless 2000 Ohms don't you?

                FWIW I was also an Instructor for Mike Holt and I am a Moderator on Mikes Code Forum. We have taught thousands of Sparkies and Train Drivers about proper grounding.

                There is only one group that can use Earth as a conductor, electric utilities. All others are forbidden to use earth as a ground, NEC forbids earth to be used as a circuit conductor no ifs. ands, or buts. If you stop and think it is crystal clear. The secondary distribution line operate at 4160 and 13.2 Kv. On say a 20 Kw transformer fed with 13.2 only requires a 2 amp fuse. A 100 Ohm ground will blow a 2 amp fuse instantly and vaporize it at 13.2 Kv. Earth cannot be used below 4000 volts effectively. Strictly high voltage game.

                Understand?

                My comments are not directed at anyone, they are directed at stupidity, ignorance, and complacency. There is only one and only one NEC requirement. If a single rod does not achieve 25 ohms shall be supplemented by one additional rod. That means drive two rods and collect a check. It can be 1 ohm or 1000 ohms. does not matter. In fact having a low resistance is dangerous.
                Last edited by Sunking; 11-15-2016, 04:08 PM.
                MSEE, PE

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                • #23
                  Tyab some food for thought. I live in paradise today, Panama. I retired and left the USA. Anyway during my career I have done a lot of mission work for the church helping folks in undeveloped countries. Some of those countries include Cuba, Haiti, Jamaica, and even Panama. All those countries have something in common, they are tropical with a lots of LIGHTNING. Thousands are killed in their homes from Lightning every year. They live in homes with dirt floors. When lightning strikes say a nearby tree, Lightning enters the ground and spreads in all directions. This causes Step Potential Difference. That means the distance between your feet will kill you because of the high current flowing through the high resistance soil you are standing on. The potential difference is enough to turn you into a crispy critter like these two fine young democrats stealing copper in TX. The conductors were part of a grounded system and they were grounded when one touched the pole and the other one via feet. You can tell the one who's feet were grounded, he is the one with his feet missing. The other guy is missing his hand.



                  There is a very easy way to prevent this from occurring. We have the locals scavenge all the wire they can find. Bard wire, phone wire, old mattresses springs, any type of wire. We dig a ring around their huts, and bury a ring of wire. That is all it takes, problem solved. The ground ring shunts most of the ground current around their homes.
                  Last edited by Sunking; 12-24-2017, 02:33 PM.
                  MSEE, PE

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                  • #24
                    Originally posted by Sunking View Post
                    Tyab some food for thought. I live in paradise today, Panama. I retired and left the USA. Anyway during my career I have done a lot of mission work for the church helping folks in undeveloped countries. Some of those countries include Cuba, Haiti, Jamaica, and even Panama. All those countries have something in common, they are tropical with a lots of LIGHTNING. Thousands are killed in their homes from Lightning every year. They live in homes with dirt floors. When lightning strikes say a nearby tree, Lightning enters the ground and spreads in all directions. This causes Step Potential Difference. That means the distance between your feet will kill you because of the high current flowing through the high resistance soil you are standing on. The potential difference is enough to turn you into a crispy critter like these two fine young democrats stealing copper in TX. The conductors were part of a grounded system and they were grounded when one touched the pole and the other one via feet. You can tell the one who's feet were grounded, he is the one with his feet missing. The other guy is missing his hand.



                    There is a very easy way to prevent this from occurring. We have the locals scavenge all the wire they can find. Bard wire, phone wire, old mattresses springs, any type of wire. We dig a ring around their huts, and bury a ring of wire. That is all it takes, problem solved. The ground ring shunts most of the ground current around their homes.
                    Sunking, I was trying to find the photo you had posted here for use as a warning to others. It appears to not be accessible through Photobucket. I'm sure you remember this image as once you see it you wouldn't forget it, oh and it's yours to begin with. Ha ha. Anyway could you repost it? It could still help others here once they see it as well.
                    Funny thing, I found this thread by searching "fine young democrats" I thought that was pretty funny and that phrase stuck in my head as well.
                    Last edited by littleharbor; 12-23-2017, 09:22 AM.
                    2.2kw Suntech mono, Classic 200, NEW Trace SW4024

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                    • #25
                      You mean these two fine gentleman?

                      MSEE, PE

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                      • #26
                        Originally posted by Sunking View Post
                        You mean these two fine gentleman?

                        There they are. Thanks, SunKing.

                        On a lighter note, Merry Christmas to you and yours.
                        Looking forward to a prosperous new year for all.
                        2.2kw Suntech mono, Classic 200, NEW Trace SW4024

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                        • #27
                          Originally posted by littleharbor View Post
                          On a lighter note, Merry Christmas to you and yours.
                          Looking forward to a prosperous new year for all.
                          Back at you, gotta go celebrate. SK signing off. Merry Christmas to all. Let there be peace on earth tonight and tomorrow.

                          MSEE, PE

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