Lighting Risk of Chimney Caps + Liners

[begreen]

This just happened this morning about 9am. I watched this storm pass about 5 miles to the east of us. We heard lots of thunder but fortunately that was all. I checked the radar and this was at max intensity. It was very lively and for this family and their fir tree, not a good way to wake up.
http://www.komotv.com/news/8490152.html

 

[Gooserider]

Back to the original post... If you don't ground your Stove/chimney you have a LOT lower chance of it getting hit by lightening.
So... Un-plug it.

If it's sitting on Concrete (stone fireplace)... It's grounded, so the plug is less of an issue. Maybe put ceramic insulators of some sort under the stove feet?

I would tend to consider this very BAD advice :exclaim: unplugged or not, the stove is still going to be grounded, albeit poorly, by the chimney structure connecting into the house frame, especially a masonry chimney. If you do get a hit, you are more likely to have damage if the chimney isn't safely grounded - the current will flow through the comparitively high resistance masonry, current through resistance produces heat, lots of it, which vaporizes any water in the masonry, such that the resulting steam pressure can blow the bricks apart explosively. In the meantime the current flows down (usually via the metal liner) to the METAL stove, INSIDE the structure, where it can cause further damage by flashing over to any nearby better conductors, such as people or electrical equipment... Unplugging the stove and attempting to insulate it will INCREASE the odds of a flashover by increasing the resistance on the stove to ground, thus making other targets more "tempting".

OTOH, if the chimney has a properly designed and installed protection system, the bolt will hit the metal protection device, then flow most of the current down the metal grounding system into the earth where it dissipates harmlessly. Note that a properly designed system can take an almost infinte number of hits without damage - the only way you'd ever know you were hit is if someone saw the strike and told you about it.

The exploding chimneys mentioned earlier were probably all "ungrounded" and demonstrated a failure to safely handle a strike. They wouldn't have been noticed if they'd been protected.

Gooserider

 

[chikey]

Our house had a fire due to a lightning strike in July. The brace on a 12 root stainless steel woodstove chimney was struck. It was next to the aluminum drip edge and a shingle got knocked off. Then the lightning ricocheted to the downspout of the gutter nearby. As a result the house walls began burning on the inside. There was significant damage, mostly water and smoke, but everyone is safe.

I am trying to determine if grounding the chimney is a good thing. I had one electrician (an old salt) tell me to ground the chimney stack. Another electrician told me grounding the chimney would only increase my chances of getting a lightning strike.
-Bruce in Boston

 

[Gibbonboy]

Um, the lightning has already jumped thousands of feet to reach your house, what is unhooking the cord and moving it at most a couple feet away going to do to stop it, other than maybe a nice cloud of plasma inside your house? I have 12 antennas of varying types on my house, ranging from huge copper wire loops in the trees on the hill behind the house, to one actually mounted on my chimney, to several mounted on the peak of the garage. I keep the cables disconnected from the inside of my house and hooked onto a grounded point outside. I hook them up in the summer only when they'll be used, and never when storms are near. I still have lightning arrestors on all cables, but that's more to discharge static during the winter.

Our towers for my work get struck all the time, one is 300 feet behind my house. Never any damage to the equipment, because it has all the proper grounding and shielding.

Lightning is unpredictable enough, though, as shown by the chimney pictures. You can't really stop it, just redirect the energy pulse quickly away from the structure. A proper ground field is critical to bleeding voltage off quickly enough to prevent damage and/or fire.

 

[builderbob]

Interesting discussion.

To ground or not to ground, that is the question.

As we will be building a new home with a ZC steel woodburning firpelace and a SS chimney, we would be most interested in incorporting "proper" lightning protection during construction. The ZC will sit on a plywood subfloor with crawlspace underneath. The SS chimney will go up thru two stories in interior surrounded by wood framing and drywall.

So do we have them put some kind of metal strap around a section of the Stainless Steel chimney, and run large copper wire from that strap down to metal pole pounded into the earth next to the house (or under the house in crawlspace)?

This to provide a path of least resistance to get the charge into the earth to dissipate?

BTB

 

[Gooserider]

Our house had a fire due to a lightning strike in July. The brace on a 12 root stainless steel woodstove chimney was struck. It was next to the aluminum drip edge and a shingle got knocked off. Then the lightning ricocheted to the downspout of the gutter nearby. As a result the house walls began burning on the inside. There was significant damage, mostly water and smoke, but everyone is safe.

I am trying to determine if grounding the chimney is a good thing. I had one electrician (an old salt) tell me to ground the chimney stack. Another electrician told me grounding the chimney would only increase my chances of getting a lightning strike.
-Bruce in Boston

I would refer to the LPI website I referenced earlier in this thread - I am NOT an expert on the subject, but my take from that site, plus other knowledge is that the reason you had the fire was that you were not adequately protected. The lightning hit your chimney structure and found it's own way to ground through conductors that didn't have enough capacity to handle the current surge. The heat from the resistance heating (plus possibly some inductive heating) led to your fire.

That you've been hit once is a strong indicator that you WILL get hit again, so adding a protection system probably won't change your odds of getting hit again, but it will decrease the odds of future hits doing damage.

BTB, I would definitely put a protection system on a metal chimney, but I suspect there may be more to it than what you suggest - I'd get pro advice on what sort of system to set up in terms of what size wire to use, how to route it, what sort of grounds to use and so on...

Gooserider