Grounding metal chimney?

[Tron]

All,

I haven't found much about this here, so I'd better ask.
We installed a wood stove plus metal chimney last year, making it the highest point of the house. It is not connected to ground as the stove sits on the concrete foundation with tiles in between, so it probably does not provide a likely pathway to ground to attract lightning. As we live in the south, severe thunderstorms are common. Most likely it will hit some of the larger trees around us (about 100ft from the house and far taller than it), I still wonder if it makes sense to properly ground the chimney by connecting it to the house's grounding rod. That would require some (ugly) wires running across the roof, but I really don't want a lightning strike to hit the chimney, travel down into the house and arrive at the stove with nowhere to go...

Thanks!

 

[begreen]

Yes, it is a good idea, especially if there is an existing system to tie in to.

Lightning

The other night during a thunderstorm, I started wondering, what happens when lightning strikes my stainless steel chimney cap that is attached to the stainless steel liner that is attached to the steel stove that is attached to the blower that is plugged into the wall socket. The chimney cap...

www.hearth.com

 

[Corey]

Interesting and timely topic - after seeing lightning strike a utility pole ~200ft away from my house a few years ago, and last year after a bright flash/immediate "KA-BOOM!" in the middle of the night, going out the next morning and picking up bark from a neighbors tree which appeared to have been struck causing the bark to explode down the trunk.

Grounding the chimney certainly would not be a bad idea, though a couple of thoughts:

If the chimney is not grounded now, it is no more 'likely' to get struck than anything else around it. The lightning is seeking a path to ground, not necessarily 'metal'. (or more likely, the ground is actually seeking a path to the sky for a typical 'lightning strike')

It would depend a bit on what you mean by 'the house's grounding rod' - if you mean an already installed lightning protection system, then yes, that would seem beneficial. If you mean the house's electrical service ground rod, then I'm not sure about that. Seems like channeling a lightning strike into the electrical service ground might not be the best thing (even an ohm or two resistance at the ground rod x 1 million volts of lightning seems like it would still be considerable current flowing 'back' into the house wiring). Seems like you'd want a 100% separate ground rod for a lightning system.

If concern is great enough to ground / lightning protect the flue, it might not be a bad idea to have a full lightning protection system forthe house (if not already). An acquaintance of mine found this out the hard way several years ago. Lets just say hilltop houses on the great plains are not the best place to chance going without lightning protection. Lightning striking a wooden house can easily cause enough resistive heating to set the wood on fire in all sorts of locations...attic, inside walls, floors, ceilings, etc. Unfortunately, the only way to get all that put out was to let the house burn to the ground and put out the 'hot spots'.

 

[begreen]

Good point about the difference between a dedicated lightning system ground and the electrical system ground. From the sound of the setup, the easiest route may be to run a dedicated ground for the metal chimney with its own ground rod.

Lighting is odd and often unpredictable. Back when I lived in CT in an upper valley, a neighbors house was struck, most likely at the utility strike coming into the house. The house was low, and single-story, with some large trees around it. It blew out the breaker panel and the telephone box too. The owner was sitting at the dining table when it happened. Said that a breaker went flying past his face.

 

[Tron]

@Corey
Yes, I agree. It's true that the chimney as of now does not represent a likely strike target. With a thunderstorm ongoing, there'll be a lot of charge in the air and an ungrounded chimney is likely to have a totally different electric potential than a grounded one. So the surrounding trees likely present a better target for the strike.

The home currently does not have a lightning protection system, and I see the reason not to connect one to the currently installed ground rod that services the house's electrical system.

Even so, my parents have it happened that (with the house having a lightning proctection system), the lightning struck a tree halfway across their yard (easily 100 yards away), which took out a lot of their electronics just as well. So you're not safe from that one, either.

 

[Bad LP]

I don’t see how it can hurt and a separate ground Rod is so easy plus a few feet of bonding wire and a couple of clamps.
Speaking as someone who has been hit twice. Not sure how the house didn’t burn to the ground to this day.

 

[Corey]

That is true. Ground rods are relatively cheap...5/8x8ft copper bonded rods look to be running about $12 each, around here. Installing separate rods from the house ground might actually allow better placement / shorter wire runs to the flue?

I lost a couple of LED lightbulbs shortly after the neighbors tree was struck Could just be coincidence, but I think modern electronics are becoming even more sensitive to voltage spikes, or possibly even a local EMP / magnetic pulse from a near-by strike.

 

[Bad LP]

That is true. Ground rods are relatively cheap...5/8x8ft copper bonded rods look to be running about $12 each, around here. Installing separate rods from the house ground might actually allow better placement / shorter wire runs to the flue?

I lost a couple of LED lightbulbs shortly after the neighbors tree was struck Could just be coincidence, but I think modern electronics are becoming even more sensitive to voltage spikes, or possibly even a local EMP / magnetic pulse from a near-by strike.

LED bulbs are a far cry from perfect. They do burn out. Also the 2 3way bulbs I bought burned out just as quickly as standard bulbs and they were around 14.00 each.
In fact replacing over 100 bulbs hasn’t effected my electric bill by any amount I can detect.
Im not impressed at all.

 

[Tron]

Offtopic, but I've seen the opposite effect. I run outside lights from dusk until midnight, and there used to be 5 100W incandescent bulbs in there. That added up to quite a few kWh. I replaced them with 10W LED bulbs and that really shows. Even better light now since the LEDs have their own reflector.
Same goes for hallway lights which is on quite often, even during the day.

 

[Highbeam]

Rather than across the roof, do you have an attic space to clamp the bonding wire to the chimney out of sight?

 

[kennyp2339]

I'm 50/50 on this, I def understand the safety aspect of grounding the stove, but if you do have larger tree's near by its not necessary since the tree's offer that direct path from sky to ground. I would think by grounding the chimney your more or less making it easier to invite a lightning strike, how the electrons line up before it strikes offering a path to ground. I dont know though, you can also just ground the stove by attaching a #6cu wire to the leg then run it to a clamp on a water pipe to, I guess it all depends on how your house is situated and what access you have to things that have a direct ground.

 

[Tron]

Rather than across the roof, do you have an attic space to clamp the bonding wire to the chimney out of sight?

That's probably not such a good idea. That grounding wire is going to carry a lot of current in the event of a lightning strike, and is going to get pretty hot. Running that out of sight in the (wooden) attic seems dangerous.

 

[begreen]

Rather than across the roof, do you have an attic space to clamp the bonding wire to the chimney out of sight?

If it is on the opposite side of the house then it might be easier to run a dedicated line down that side of the house.

 

[Bad LP]

That's probably not such a good idea. That grounding wire is going to carry a lot of current in the event of a lightning strike, and is going to get pretty hot. Running that out of sight in the (wooden) attic seems dangerous.

I manage two large properties fulltime and the ground wires for the lightning rods are all braided bare copper.

 

[Highbeam]

That's probably not such a good idea. That grounding wire is going to carry a lot of current in the event of a lightning strike, and is going to get pretty hot. Running that out of sight in the (wooden) attic seems dangerous.

From what I understand it’s high voltage but low amperage. Short term as well.

 

[Tron]

From what I understand it’s high voltage but low amperage. Short term as well.

It's both high voltage and high amperage. Easily gets into kA and MV. But yes, only a very short duration, less than a ms.
That's the only reason why an 8-ga wire can withstand it.

 

[David.Ervin]

It's worth talking to an electrician about installing a grounding rod for the chimney. By code, it may have to be bonded to the same ground as the rest of the house to make sure it's at equal potential, and also that it doesn't give you a nasty surprise by carrying a bunch of current to ground in the event of some electrical short involving your stove, blower, chimney, etc. There's a fairly hair-raising pic on the internet of a gas line for a water heater glowing cherry red due to the home's main ground breaking, and all the electric current flowing back out through the water heater and that line to find ground.

 

[clancey]

You people are scaring me---do I have to have a grounding wire when I put in my wood burning stove with a 12 foot double insulated metal pipe sticking up on top of the roof...Is this something that I should be concerned about because we get a lot of lighting strikes where I live but mostly in the mountains.. Why can't you simply ground your stove somehow like ask a electrician or something because i am going to ask mine at this point...Should I be concerned about this...? clancey

 

[Highbeam]

We have lots of lightning too and I am not concerned about this at all. Mobile home installations require bolting the stove down and grounding the stove.

 

[EbS-P]

Remember this lightning bolt has enough electric potential to arc through the air. The physics of lightning protection systems is not just to provide a path to ground but also as a way to dissipate charge from the area nearest your house. Say the clouds are positive and the ground is negative. The largest potential exists where the accumulation of negative charge is the greatest. If you are able to leak negative charge back to the atmosphere you lessen the electric potential difference and hope that some near by object is at a higher potential difference and thus lightning is more likely to hit the other object and not your house. This why good lightning protection systems have multiple grounding points with multiple pointed lightning rods. The point creates a stronger electric field in the region around the point making easier for charges to be removed. Physics lesson over. Personal opinion not supported by any hard facts but my own reasoning though things.
Grounding the chimney could help dissipate excess charge which could be a good thing. I could see a situation where the chosen location of the ground rod for what ever reason means the chimney is at a higher potential and negates any benefits or could even make things worse. I don’t think that any conductor used could “carry” any significant current of the lightning strike rather it provides a path of constant potential for the strike to follow... until it doesn’t.
Any strike to the house, grounded chimney or not will do significant damage. Before I grounded anything I would have talk with my insurance agent and make sure I have appropriate coverage and a deductible that I’m comfortable with.
If this is all in the name of personal safety there are probably other areas to invest in that statically would make you safer than grounding the chimney. Upgrading to arc fault breakers ( way more house fires occur due to appliance failures than lightning) or new tires (or a new safer vehicle). Personally I would only tie it into an existing system.
Evan.

 

[Tron]

Remember this lightning bolt has enough electric potential to arc through the air. The physics of lightning protection systems is not just to provide a path to ground but also as a way to dissipate charge from the area nearest your house. Say the clouds are positive and the ground is negative. The largest potential exists where the accumulation of negative charge is the greatest. If you are able to leak negative charge back to the atmosphere you lessen the electric potential difference and hope that some near by object is at a higher potential difference and thus lightning is more likely to hit the other object and not your house.

Actually, my understanding of Physics says it's the other way around. If a thundercloud is charged positive (just assuming), and ground potential is zero, then a grounded rod (or chimney) will provide the largest potential difference and thus the highest likelyhood for a strike. If the chimney is not grounded, it will get a positive potential somewhere above zero, lessening the potential difference between it and the cloud. In that case you might get zapped with static electricity if you touch the stove, though.

And yes, grounding rods and wires are designed to withstand a strike and dissipate the energy into the ground. Yes, it's kA and MV, but a very short duration, so for instance a 8-ga wire does heat up significantly but not to the point of failure.

But you are right, a strike either into a grounding rod or even into a nearby tree can seriously mess up your electronics, just by the voltages induced into your house grid.

 

[Highbeam]

But what about asteroid strikes?

 

[Tron]

But what about asteroid strikes?

I guess we're out of luck here. Fortunately, they're rather rare ;-)

 

[begreen]

We have lots of lightning too and I am not concerned about this at all. Mobile home installations require bolting the stove down and grounding the stove.

WA is comparatively low on the lightning strike list. In 2019 there were about 183,000 strikes here. Compare that to the top 10 states:

1. Texas: 16,032,609
2. Kansas: 8,299,321
3. Nebraska: 6,166,469
4. Oklahoma: 6,039,749
5. Florida: 5,271,987
6. Missouri: 4,612,813
7. South Dakota: 3,706,174
8. Iowa: 3,603,519
9. Colorado: 3,499,283
10. New Mexico: 3,436,976

Which States Have the Most Lightning Strikes? - Earth Networks

Just how many lightning strikes did your state see this year? Note: This page reflects lightning data captured by the Earth Networks Total Lightning Network (ENTLN) in 2019. For the latest data from our 2022 Lightning Report, click here. The Top 10 States with the Most Lightning Strikes in 2019...

www.earthnetworks.com

 

[clancey]

What a fun mapping to play with and yes my state is among those with more strikes..I hope it doesn't get me or my new stove pipe..clancey.