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Grounding chimney liner & lightning protection

Post in 'The Hearth Room - Wood Stoves and Fireplaces' started by Green Energy, Oct 5, 2009.

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  1. Green Energy

    Green Energy Feeling the Heat

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    I just put in a SS liner and ready to install the stove. I was sitting outside looking up at the chimney. I have a TV antenna mounted on the chimney and remembered how the antenna installation instructions said to ground the antenna. So I installed a three conductor 12 or 14 gauge copper electrical conductor that I connected to the antenna and dropped to the ground and connected to a grounding stake. (I am on well and septic so I don't have copper pipes to ground to.) So I thought, wow, maybe I should connect this grounding wire to the chimney liner as well.

    I searched the forums previous articles and follow a few threads. The most comprehensive is:

    http://www.hearth.com/econtent/index.php/forums/viewthread/8187/

    It seems to be smart to have the chimney with a metal liner going into the house to be grounded. However, there also seems to be a lot of confusion about the lighting protection. I am still not sure whether to connect my antenna ground to the chimey because the antenna is directly above the chimney cap, would most likely get hit by lightning before the chimney cap, and there is three 12 or 14 gauge conductors grounding the antenna that run OUTSIDE the house to ground. So I am not sure in my case that connecting the chimney to the antenna ground would help. I am thinking if I do anything, I might put a separate ground on the chimney, not connect it to the antenna.

    Any further consensus on grounding in general or insight into the situation that I presented above?

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  2. Cluttermagnet

    Cluttermagnet Minister of Fire

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    There is indeed a lot of confusion about lightning protection. It's a fairly technical subject. Although lightning does at times seem 'freakish' or magical in its behavior, it does nonetheless follow well understood physics laws. As always, "the devil is in the details".

    I believe that tying in the new chimney liner to your existing rooftop TV grounding setup is asking for trouble. In the event of a major strike to the roof of your house, you would effectively be inviting a portion of the strike inside your house- with 'nowhere to go', once inside. Bad idea! Even if your existing rooftop down conductor performed exactly as you intend (it may well not), the current might already be so intense that you could expect a direct strike to set your roof on fire under that piece of Romex (sounds like that is what you used to ground the TV antenna). And you want to divert some of that strike down your chimney? It could arc to who knows what inside your living space. Definitely do not tie that liner into any rooftop conductors IMO.

    One internationally recognized authority on lightning mitigation is Polyphaser Corp. in Minden, Nevada.
    Their home page is here: Polyphaser
    Their sub-page on grounding is here.
    They have a page listing tech papers here.

    The article titled "Ham Radio.pdf" probably would be a good place for you to start. You'll get some of the flavor of it, anyway. It gets a little heavy. Your eyes may glaze over. Don't feel bad, however- many folks, who understand electronics well, do not understand the finer points of lightning mitigation very well at all. It is a whole sub- specialty unto itself, and it takes a little effort to grasp the underlying principles. Me? I worked as an electronics design engineer and for many years as an active radio hobbyist. I understand the practical physics but still am basically a layman in this area, not an 'expert'.

    If you want to ask some more questions about your setup and can supply a little more detail, I'll try to help you understand the basics of your particular situation.
  3. Green Energy

    Green Energy Feeling the Heat

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    Great advice, I was thinking similarly that I did not want a strike on the antenna to have a direct pathway to the chimney. I am using romex with all the conductors joined. It hangs free of the roof, a couple feet off the chimney and runs to ground. I'm thinking of leaving the chimney alone.

    Great quote on your signature line, lol!
  4. Malak

    Malak New Member

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    I used to fix alarm equipment and the grounded panels were much more likely to fry.

    I think the best thing to do might be an air-gap ground i.e. it is not grounded normally, and therefore not attracting a strike, but IF it occurs then it has a path! (I smell a patent or Nobel prize...)

    Had my stove for a year with no grounding and no problem so far.
  5. Cluttermagnet

    Cluttermagnet Minister of Fire

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    That makes sense. When lightning is seeking a path to ground, a strike will divide however it needs to, to get there and dissipate. Few attempts at grounding implement the correct 'single point ground' concept very well- or at all. Those 'grounded' panels can make a more tempting target oftentimes- by offering the strike a lower impedance to ground from the metal enclosure. Yet during a microseconds long lightning strike, a marginally grounded enclosure can be elevated thousands of volts above true earth potential. There are so many variables in any given setup. The exact grounding configuration in use is but one of many factors in play.
  6. Malak

    Malak New Member

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    Interesting twist on dissipating the charge to prevent the strike...

    Attached Files:

  7. Cluttermagnet

    Cluttermagnet Minister of Fire

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    Wow! Interesting indeed. Thanks for sharing the photo. That's a pretty controversial area of lightning protection, BTW. Strong opinions on both sides. Some claim it's quite effective in preventing strikes, others claim it's been proven ineffective, so that controlling the current flow during a strike is a better, more realistic, and more effective strategy. It's way above my pay grade. :)
  8. Wood Heat Stoves

    Wood Heat Stoves Minister of Fire

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    typically liners are stainless, which i believe lighning has less affinity for then other types of metal. someone pls correct me if i mis speak...
    anyway, liners are typically not specifically grounded outher than contact with the brick foundation, which is usually well grounded
    grounding is typically only required in mobile and modular homes for a reason..
  9. Rockey

    Rockey Minister of Fire

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    Lightning protection is not a DIY project. Lightning protection is used in many applications with limited success i.e. Faraday cages and 45 degree cones of protection in electrical substations. As someone eluded to earlier, lightning propagation is a hotly debated subject with no real consensus on 100% protection. I wouldnt touch this one with a 10 foot lighning pole.
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