Choking the ground electrode conductor

vtmapsvtmaps Posts: 3,738Solar Expert ✭✭✭✭
I was just looking at this article:

http://www.homepower.com/articles/solar-electricity/design-installation/ask-experts-pv-grounding

and they had smart suggestion that I have not seen mentioned on this forum:
For good lightning protection, it seems like the PV array ground wire should be bonded to a ground rod at each pole, tied to the array’s emergency disconnect switch box and that box bonded to its own ground rod. The ground wire should then be coiled into a choke and bonded to another ground rod just before it enters the house and goes to the inverter.

A choke in this circumstance does not interfere with safety grounding, but may help keep high frequency components of lightning out of your home and equipment in the home.

Can anyone explain to me why the best location for the choke is at the house end of the GEC rather than the array end of the GEC?

btw, chokes are commonly used in electric fences... I used to put a choke in the HOT wire of my electric fence to block lightning induced high frequencies in the hot fence wire from frying the fence charger.

--vtMaps
4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i

Comments

  • solarixsolarix Posts: 713Solar Expert ✭✭
    Re: Choking the ground electrode conductor

    I thought the HomePower answer was very well done. You want the lightning protection to have a low impedance (not choked) route to ground but to have a relatively high impedance route to your home and electronics - thus the choke before going into the house. The NEC even requires that if you run the GEC inside a conduit, you bond it to the GEC on both end of the conduit to lessen the conduit to act like a choke.
  • nsaspooknsaspook Posts: 396Solar Expert ✭✭✭
    Re: Choking the ground electrode conductor

    I really don't like the idea of putting inductance (series protection device) in any ground electrode because it makes it an antenna instead of a ground plane and when you have an antenna, direct coupling from wiring currents is not all you have to worry about. Chokes store energy when current flows thru for any reason creating a imbalance of energy fields (voltage differential) from the house ground wiring and ground rod if there is any leakage (at high frequency there will be a capactive path to ground) to ground inside the house from a point other than the ground rod. Series protection is ok with HOT wires combined with shunt protection to a very low inductace ground to reduce the signal delta from the power lines power to ground. The way to keep high frequency components of lightning out of your home is for you have the lowest possible inductance in your grounding system and power wire shunt protection (with capacitor shunt filters for HF energy) devices connected to that ground.
  • nielniel Posts: 10,311Solar Expert ✭✭✭✭
    Re: Choking the ground electrode conductor

    technically either way it is an antenna and all you are doing with a coil is changing the resonant frequency to a lower one. i don't think this will do much anyway in resisting the flow of currents from lightning and one does not want to add further dc resistance to ground for sure. i can understand the concept in that they are trying to keep the lightning energy from entering the house and any effort there must allow for it to flow to ground before it enters the house. so would i put a coil of wire there even if the wire went to ground outside? no. if one wishes one can then put some toroidal cores with a pass or 2 of the wire going through the core that would increase the inductance without adding much more wire or dc resistance on the wire entering the home. an idiot inspector will probably disallow it anyway.
  • nsaspooknsaspook Posts: 396Solar Expert ✭✭✭
    Re: Choking the ground electrode conductor
    niel wrote: »
    technically either way it is an antenna and all you are doing with a coil is changing the resonant frequency to a lower one.

    Yes but it can be more of an 'antenna' to your equipment if it's isolated.
    The RF choke coil/AC isolator (just like the choke in a old tube RF output stage) won't change the resonant frequency of the internal conductors much but what it will do is isolate the houses ground wiring at anything but a few parasitic RF parallel or series frequencies and may actually enhance instead of decrease the amount of EM energy received from a near strike (with a direct strike all bets are off the table) that arrives at the house from the resultant EM fields. At DC we can usually assume the electrical energy is actually in the conductor (it's always in fields around the wire instead, always) so when we have a conductor that's the current path for the signal but at RF we all know it's coupled by fields that don't need wiring to move into space. The RF energy from the strike that needs to be reduced most likely didn't orginate from current in that ground wire directly from the bolts current, it was coupled to the space around the strike and induced into the wiring by electromagnetic induction or RF radiation. If all our conductors are good conductors and have a good path to ground most of the induced current will flow that way and constrain the fields near them instead of into our precious electronics that are bonded to that ground.
  • nielniel Posts: 10,311Solar Expert ✭✭✭✭
    Re: Choking the ground electrode conductor

    it would only enhance it at its resonant frequency, but i'm not arguing in favor of using a coil anyway so the particulars are moot being we agree on not using it.
  • vtmapsvtmaps Posts: 3,738Solar Expert ✭✭✭✭
    Re: Choking the ground electrode conductor
    nsaspook wrote: »
    I really don't like the idea of putting inductance (series protection device) in any ground electrode because it makes it an antenna instead of a ground plane and when you have an antenna, direct coupling from wiring currents is not all you have to worry about. Chokes store energy when current flows thru for any reason creating a imbalance of energy fields (voltage differential) from the house ground wiring and ground rod if there is any leakage (at high frequency there will be a capactive path to ground) to ground inside the house from a point other than the ground rod. Series protection is ok with HOT wires combined with shunt protection to a very low inductace ground to reduce the signal delta from the power lines power to ground. The way to keep high frequency components of lightning out of your home is for you have the lowest possible inductance in your grounding system and power wire shunt protection (with capacitor shunt filters for HF energy) devices connected to that ground.

    I think I follow your logic, but I also think it does not apply to the situation in the article. In the Home Power article the choke is in the GEC between two ground rods. The GEC from the house goes directly (no choke) to the ground rod at the house. The GEC at the array goes directly (no choke) to the ground rod at the array. The choke is in the GEC between the two ground rods.

    When lightning strikes or induces high frequencies at the array, it has a direct path to ground at the array. The choke, with its inductance, makes it more likely for those high frequencies to go to ground at the array, rather than travel through the choked GEC to the house ground.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • CariboocootCariboocoot Posts: 17,615Banned ✭✭
    Re: Choking the ground electrode conductor

    The connection between two ground rods should never be in "an antenna state" as described.
    Hence the NEC requirement that such connections are made underground to comply with single point grounding description.

    In other words if it were wired as described it would be in code violation regardless of any lightning/RF issues.
  • vtmapsvtmaps Posts: 3,738Solar Expert ✭✭✭✭
    Re: Choking the ground electrode conductor
    In other words if it were wired as described it would be in code violation regardless of any lightning/RF issues.

    Just to be more unambiguous... are you saying that Home Power magazine is showcasing a system that violates NEC?

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • CariboocootCariboocoot Posts: 17,615Banned ✭✭
    Re: Choking the ground electrode conductor
    vtmaps wrote: »
    Just to be more unambiguous... are you saying that Home Power magazine is showcasing a system that violates NEC?

    --vtMaps

    You tell me.
    Are they describing a grounding system that utilizes two Earthing rods or plates?
    Are they advocating connection between said rods or plates be above ground?
    Does this constitute a multi-point grounding system?
    Is that allowed under NEC?

    Interpretation is half the battle.
  • nsaspooknsaspook Posts: 396Solar Expert ✭✭✭
    Re: Choking the ground electrode conductor
    vtmaps wrote: »
    I think I follow your logic, but I also think it does not apply to the situation in the article. In the Home Power article the choke is in the GEC between two ground rods. The GEC from the house goes directly (no choke) to the ground rod at the house. The GEC at the array goes directly (no choke) to the ground rod at the array. The choke is in the GEC between the two ground rods.

    When lightning strikes or induces high frequencies at the array, it has a direct path to ground at the array. The choke, with its inductance, makes it more likely for those high frequencies to go to ground at the array, rather than travel through the choked GEC to the house ground.

    --vtMaps

    That's better than directly in the GEC but still has the effect of increasing the RF voltage differential and RF power between the two rods that can make the grounding system a power generator of RF instead of a sink. The whole point in grounding IRT induction effects is to reduce voltage potential between points so large electric fields are not generated from the intense magnetic field of the strike. You can't really shield or stop that magnetic field and it's current flow with conventional grounding but you can shunt voltage potentials to prevent the generation of an electric field so one side of the electrical power equation is missing. P=I*V
  • Dave AngeliniDave Angelini Posts: 3,776Solar Expert ✭✭✭✭
    Re: Choking the ground electrode conductor

    Agree and add an XW system or Inverter with intelligence that can shut down the inverter/system in a close strike with sensing from the GFCI. After that it is just your Karma or Prayers!
    solarix wrote: »
    I thought the HomePower answer was very well done. You want the lightning protection to have a low impedance (not choked) route to ground but to have a relatively high impedance route to your home and electronics - thus the choke before going into the house. The NEC even requires that if you run the GEC inside a conduit, you bond it to the GEC on both end of the conduit to lessen the conduit to act like a choke.
    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
     http://members.sti.net/offgridsolar/
    E-mail [email protected]

  • nielniel Posts: 10,311Solar Expert ✭✭✭✭
    Re: Choking the ground electrode conductor

    coot,
    the nec, or should i say wiles, does advocate separate grounds not connected under ground. my complaint against wiles was requiring the ground wire to travel with the pv wires to the house even if one elected to bond the rods underground. that makes the ground wire traveling with the pv wires a redundant secondary path to ground through the house that can not only create loops, but will endanger life and property inside during a strike being it is piped into the house, if one has the pv rod bonded underground with the main rod at the house. i can understand not bonding the rods together only if we are talking some distances between them whereas the earth resistance could then stop the loops and high voltage differentials from developing. then the ground wire with the pv wires is warranted, but still a danger as the path to ground is through your place.

    interestingly enough if one does the underground bond and has the redundant ground wire with the pv wires the choke could help reduce some problems due to ground loops, but it'll do nothing worthwhile against the power of a lightning strike near or direct. the crux of it is they are trying their best to come up with round about fixes to the problems they are creating in requiring that visible ground wire with the pv wires and the lightning dangers that this wire presents to the occupants and property. they can't verify a ground that is buried because they can't see it. simple to fix as the inspector could see it before or as it is being buried. that makes too much sense doesn't it?!?!?!
  • CariboocootCariboocoot Posts: 17,615Banned ✭✭
    Re: Choking the ground electrode conductor

    Niel;

    Yes, that makes sense.
    So we'll have none of it in our regulations! :p

    There is also the concern that people may think this will 'prevent' damage from lightning, as with all such precautions. It can't. Risk can only be reduced, never eliminated.

    And if the effort to reduce the risk under one set of circumstances results in an increased risk under another you can debate endlessly which is the likely greater risk. This is in fact what happens and why the NEC keeps changing - and no one can keep up with it.

    Out of curiosity, how would one construct this 'choke'? How many turns of wire of what diameter, of what gauge, and with or without a core? You can play with that 'til you go crazy too.
  • nsaspooknsaspook Posts: 396Solar Expert ✭✭✭
    Re: Choking the ground electrode conductor

    I would listen to Mike Holt, he has it right. You don't want isolated grounds (by a choke or by not being bonded) or even extra ground rods and connections unless they are needed.
    https://www.youtube.com/watch?v=YuDqXFvRv94
  • CariboocootCariboocoot Posts: 17,615Banned ✭✭
    Re: Choking the ground electrode conductor
    nsaspook wrote: »
    I would listen to Mike Holt, he has it right. You don't want isolated grounds (by a choke or by not being bonded) or even extra ground rods and connections unless they are needed.

    Well I'm glad there's somebody in this world that agrees with me on something. :D
  • nsaspooknsaspook Posts: 396Solar Expert ✭✭✭
    Re: Choking the ground electrode conductor

    When I read the history of PV grounding in the CODE it looks like a horror story. This is what John Wiles says about the aux ground mess that was added in 2008, pulled in 2011 and put back in today.
    Conflicting proposals for Section 690.47 in the 2008 NEC resulted in a code requirement that was written in a hasty, last minute manner during the last Code Making Panel (CMP) meeting of the 2008 NEC cycle. It was not reviewed by anyone outside of the CMP and has both grammatical and technical errors. Because this type of code writing —which included no public review and commenting period—violated NEC code development procedures and because of other issues, the National Fire Protection Association has disbanded this CMP.

    http://solarprofessional.com/articles/design-installation/additional-electrodes-for-array-grounding/page/0/2

    I don't see much change. :grr
  • Dave AngeliniDave Angelini Posts: 3,776Solar Expert ✭✭✭✭
    Re: Choking the ground electrode conductor

    I use John Wiles. He actually does the testing ! He has since I was just a little guy! His story of ball lightning still cracks me up!

    http://solarprofessional.com/articles/design-installation/additional-electrodes-for-array-grounding


    nsaspook wrote: »
    I would listen to Mike Holt, he has it right. You don't want isolated grounds (by a choke or by not being bonded) or even extra ground rods and connections unless they are needed.
    https://www.youtube.com/watch?v=YuDqXFvRv94
    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
     http://members.sti.net/offgridsolar/
    E-mail [email protected]

  • nielniel Posts: 10,311Solar Expert ✭✭✭✭
    Re: Choking the ground electrode conductor

    it kind of is an admission of not knowing what they are doing eh? gee, like we didn't already know that. i wonder if that guy from elsewhere who proclaims to be a king had anything to do with much of that idiocy too?
  • Dave AngeliniDave Angelini Posts: 3,776Solar Expert ✭✭✭✭
    Re: Choking the ground electrode conductor

    The NEC is one thing but John's advice over the years for remote offgrid array wiring and his testing with lightning has saved quite a few installations.
    nsaspook wrote: »
    When I read the history of PV grounding in the CODE it looks like a horror story. This is what John Wiles says about the aux ground mess that was added in 2008, pulled in 2011 and put back in today.



    http://solarprofessional.com/articles/design-installation/additional-electrodes-for-array-grounding/page/0/2

    I don't see much change. :grr
    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
     http://members.sti.net/offgridsolar/
    E-mail [email protected]

  • nsaspooknsaspook Posts: 396Solar Expert ✭✭✭
    Re: Choking the ground electrode conductor
    The NEC is one thing but John's advice over the years for remote offgrid array wiring and his testing with lightning has saved quite a few installations.

    From what I have read about the guy that's true, so his pushing of these confusing and sometimes contradictory grounding requirements is a head-shaker for me.

    For the record on how the current code section was created.
    Attachment not found.Attachment not found.
    http://www.solarabcs.org/codes-standards/NFPA/pdfs/2014NEC2%20690.47%28D%29%204-232a.pdf
  • BB.BB. Posts: 27,588Super Moderators admin
    Re: Choking the ground electrode conductor

    IMHO--The confusion is because there are multiple reasons for Grounding an electrical system. And some of the requirements are difficult to merge together into one all encompassing document that will work for everyone.

    1. Grounding for Local Safety (i.e., Grounded AC Neutral so that fuses/breakers only needed on "hot" leg of power)
    1.1 Grounding to trip Fuses/Circuit Breakers when fault (grounding plumbing/gas lines/etc. to turn off electric power)
    1.2 Ground Fault Sensing (AC) (Ground Fault Interrupter breakers/outlets to prevent electrocution)
    1.3 Neutral Bonding/Polarizing of AC plugs/wiring (so single pole switches can be used to turn off "hot" power legs)
    2. Grounding for Distribution Safety (i.e., crossing 12,000+ Volt distribution lines to 120/240 VAC power drops)
    3. Grounding for Lightning Safety (get energy from strike to ground before gets into home)
    4. Grounding for Personal Safety (no hot metal that a person can touch and get electrocuted)
    5. Grounding for Operational Reasons (florescent lamps/electronic natural gas ignition systems that need "earth ground")
    6. Grounding for EMI reduction (conducted radio frequency noise from power supplies/equipment feeding back into main power lines)
    7. Grounding for Fault Detection (to "detect" hot/return faults in solar array to reduce chance of arc faults)
    8. Grounding and Isolation+DC Offset to reduce electrolysis (reduce chances of stray currents corroding buried pipes/tanks/structures/boat/marina/etc.).

    Each has its own requirements. And there are local (to the home) and wider (to the home+out building+other homes+etc.) effects that need to be taken into account. And frequency related affects too (DC, 50/60Hz, Lightning frequencies, Radio Frequencies, etc.).

    It is not a simple thing to document and solve.

    And when is a solution "good enough" or a new solution creating more problems than it may be worth (the whole DC Ground Fault, DC Arc Fault, and AC Arc Fault issues).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Dave AngeliniDave Angelini Posts: 3,776Solar Expert ✭✭✭✭
    Re: Choking the ground electrode conductor

    Nicely said Bill ! If you ever have a hard time sleeping the NEC confusion is helpful. None of the inspectors in my county have ever said anything about Offgrid electrical. I think they just are happy issuing a certificate of occupancy because they can start taxing. How about that Tax code for bedtime sleep problems?
    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
     http://members.sti.net/offgridsolar/
    E-mail [email protected]

  • nsaspooknsaspook Posts: 396Solar Expert ✭✭✭
    Re: Choking the ground electrode conductor

    Bill, as usual is right on the money. I'm just glad I only have to deal with the simple problems, the electricians tie the power to the equipment main disconnect, then it's my baby and IEEE rules for industrial and commercial power systems from that point on for electronic grounding/bonding requirements...
  • nielniel Posts: 10,311Solar Expert ✭✭✭✭
    Re: Choking the ground electrode conductor

    that was a good summary of it bill. although wiles tries, he lacks the knowledge and understanding of those other areas enough to legislate rules and regulations for them and it is also true of many of those co-writing those rules and regulations. they are acting more like politicians dealing in their own opinions and making it affect all. they also feel compelled to justify their positions just like politicians by continuing to make these rules and regulations over and over again.
  • CariboocootCariboocoot Posts: 17,615Banned ✭✭
    Re: Choking the ground electrode conductor

    And this is why people who have little understanding of the complexities are confused by engineers not agreeing on the 'right' way to do grounding or lightning protection. As with everything else there's more than one way and each has its advantages and disadvantages as well as major function (be it safety grounding, RF shielding, lightning protection, etc).
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