Lightning ground rod

[nickel plate]

We are in the planning stages of building our new home which is at 2500 ft elev on the western face of the northern California Sierra range and are considering an 8/12 pitch metal roof. The home will be out in the open, nearest trees will be about 50 foot away. Due to the high frequency of summer lightning storms, do we need to address a ground rod from the metal roof to deep soil embedment?

 

[SPIKER]

I would consider talking to and or putting in by a professionally installed lightning rod service. grounding/Bonding the roof is OK but will end in damage to the roof IF and WHEN it is hit. The metal is a good conductor but will super heat when it passes the amount of amperage that a lightning bolt has in it. The service should be able to install insulated stand off wire & rods so that the lighting charge is minimized prior to getting enough voltage to produce a strike. If a strike happens the Rods & Conductors will divert the charge around the structure and will most often require service after a strike or at least a good inspection.

Mark M

 

[eepete]

I have a metal roof, and thought long and hard about grounding it. The company that put in the roof had all horror stories about having someone install lighting rods on it. I also have all metal 6" gutters and metal 4" downspouts on the roof. So I decided to connect each gutter to the roof with a 2" 1/2" wide stainless steel strap, and then took the bottom of each gutter and tied it into a ground. I have 3 roofs with the following connection scheme: 1 connection (smallest, hidden section), 2 (fairly large roof over garage) and 6 (main roof).

The ground system is 1200 feet of copper. 600' in the ground around the house and some other areas, about 400' of #2 and 200' of #6. Easy to do with new construction. Then I have four 150' runs in various trenches that come out from the house for other services. The ground system connects to the AC ground at one point inside the house right at the service entrance.

Here are pix of the ground connection and the gutters. A stainless steel hose clamp goes to a stainless steel strap, then the copper connection point and copper ground wire. You should not connect copper to galvanized metal directly. You will get galvanic corrosion. You need to inspect these points annually. I spray some lub on them in the hopes that it will go where water might go and thus cut down on any chance of corrosion. This year I might spray with Fluid Film.

Disclaimers: This system design is a SWAG on my part, but I've been involved in lighting protection work in the past. I suspect this is better than nothing, but there is the chance of damage to the roof if it takes a strike. I'm balancing the chance of that damage vs. the damage of a bad installation of a traditional lighting rod system. The traditional lightning rod system can handled a larger current strike better.

Lightning data/folklore: Way back in time, the Bell System did a lot of studies on lightning. There are some pieces of that which stuck with me. A bolt of lightning can have as little as 5,000 amps and as much as 500,000 amps of current. The "typical" or average current is about 20,000 amps. So you can do a SWAG system, take a hit, do just fine, and think you've got it. Then you get a 100,000 amp strike and the results are very different. So to me a lighting protection system moves the decimal point on the odd that you'll get a strike and be destroyed over a place or two. The 2nd half of all lightning protection systems is good full replacement insurance.

A 1.5" copper strap is used a lot for commercial protection. A 6" strap (or two or three of them) is what you see on a cell tower at the bulkhead where the cables enter the building. So my little 1/2" stainless steel is the weak link, but there are a few of them per roof and their length is only 2" long. If I got a big strike, it would vaporize and I'd have some repair work.

I've seen about 3 houses that got hit with lightening and had shingle roofs. The lightning traveled on the shingles until it hit the aluminum facia (plastic covered). It then traveled around the house and found the coax coming from the satellite dish. That coax was vaporized down to the protection block. The ground off that block was often a #10 to a bad ground rod or the telephone/AC ground. Other than the entry and exit points, the facia was OK. Now if any of those houses had a high current hit, they would be on fire. So I'm _hoping_ that the roof, gutters, and downspouts have plenty of area, the #6 ground wire (which is also what is used as the ground wire on a telephone or power pole) is big enough, and the ground ring is OK.

The topic of whether or not you can dissipate enough charge through some system to avoid a strike has been debated forever. I suspect that in some cases it makes a difference, in others it doesn't. What is clear (and SPIKER refers to this) is that after a strike you must inspect the system for damage. It is not uncommon for a single ground rod to be bad after a strike. The more surface area in your grounding system, the better it can take multiple hit. One tower I have some equipment on has over 100 ground rods and can take multiple hits with no worry about the quality of the ground. There is a device your power company may have that can measure the impedance (resistance) of your ground system, they may be able to help you after a strike.

Key idea here is that a single ground rod, IMHO, is really not enough. Since the OP is building a home, there should be plenty of opportunity to put some wire in the ground around the home and get a good ground system.

Other comments: When I was doing the ground system, I went to a marine store and bought a large and small zinc anode. I connected them both. The large is down deep in the ground, the small is where I can dig it up every 5 years to see how the anodes are doing. The buried propane tank has it's own anode it came with, and that is tied into the system too. The goal is simple- if there are any problems with galvanic corrosion I want to eat up the anodes.
Be sure to put a whole house surge protector in the breaker box, and that AC ground should tie into the lighting ground at one point with a #6 wire.
If you are handy with things, and are around during construction this approach is cheap and easy. If you are at all uneasy about this approach, pay someone to put in a system but go talk to a few people they have done jobs for to see if they know how to work with/on a metal roof.

Hope this helps, another too long Pete post Wish I could preview the pix, don't know why the rotation happens.

Pete

 

[Coyote machine]

I used to have lightning rods installed on my house when I had only asphalt shingles now that I have part metal and part asphalt i have removed the lightning rods. The rods and ground spikes in the ground were here when I bought my house in 1986. We've had plenty of strikes in the area, but none have hit the house directly, to my knowledge. My power is buried from about a couple of hundred feet from the house to the entry through the basement wall.
We removed the rods from the roof to make for a cleaner install of the new roof and the transition between the metal and asphalt portions. And there are differing thoughts on what attracts lightning to lightning rods, etc. First it the fact that a rod on a house sticking up in the air will allow the connection between ground and the lightning to occur at exactly those points on top of one's house. Essentially the charge conditions are right in the atmosphere and the spike sends UP a small 'tracer' that connects to the big charge in the sky and whamo (technical term) the circuit is completed to ground. Depending on the charge and resistance to it things get fried or not along the way to ultimate ground. This all occurs in less than a very small amount of time, and can do damage or not depending on many factors, many of which are not clearly understood.
So to have lightning rods to protect from a possible random strike is a question not easily answered with any amount of certainty. One could conclude having rods sticking up from one's house/barn/ chicken coop might bring what one desires to keep away directly to where one is trying to keep the lightning from striking. On the other hand, not having lightning rods is not going to prevent lightning from striking a house roof of metal, or for that matter asphalt; especially since things like satellite dishes and other metal objects like a chimney cap are similarly prone to making the connection to the large charge in the sky.

Another thing I don't quite understand is how eepete gets water to flow in the gutter in pic #3

 

[eepete]

Coyote, that gutter only works in a _really_ hard, driving rain :laughing:

MAC computer seems to know how to deal with the rotation when I display the picture, but when I upload they are sideways. I think I have to import them, rotate, and write out the get it correct.

Pete

 

[Coyote machine]

What's a Mac?:laughing: Did you say you are sending your pics from McDonalds?!
Are you previewing your post before 'sending' it to the forum? It might help determine which way each pic will display so you can correct it before posting it.
And if you import the pics like you said it will likely make your 'Toyota computer" (aka MAC) spit out the pics like normal pc's do all day long:confused2:

 

[Kubota-guy1911]

As one who installs lightning protection systems, please look at these 2 web sites. I have purchased a lot of material from both. Thompson Lightning Protection and Harger Lightning Protection.

It it critical to use the proper type down conductors, approved fittings, bonding straps and clamps, and air terminals. We exothermically weld all connections underground. If this type work is not done correctly, your risk for damage actually increases. NFPA 780 is the "bible" for lightning protection work.


TLP Systems

harger.com


kj

 

[Gator6x4]

We are in the planning stages of building our new home which is at 2500 ft elev on the western face of the northern California Sierra range and are considering an 8/12 pitch metal roof. The home will be out in the open, nearest trees will be about 50 foot away. Due to the high frequency of summer lightning storms, do we need to address a ground rod from the metal roof to deep soil embedment?

For a down loadable manual in PDF format on Residential Lighting Protection go here.

http://www.lightningsafety.com/nlsi_lhm/IEEE_Guide.pdf

 

[eepete]

Coyote: I'll look for the preview functionality, tnx. Jumped to MACs when I tried Vista, just got tired of PCs. But MACs still have their rough edges.

Gator6x4: That a good guide. All my AC, telco, satellite, video surveillance, etc. is done in a manner that that guide suggests. The mix of MOVs in the breaker panels _and_ protected strips at all electronics devices is a good one. Gas tubes for low voltage at the entrance, then I've made circuit boards for 2nd level protection using PTCs or fuses and power Zeners. My 4 panel boxes are in one spot so the radially distributed AC has no ground loops. While telco just about always enters at or near the power, it amazing how many satellite systems come in far away from the power and introduce bad ground loops.

Kubota-guy: All the ground wire is properly connected. Where I'm unorthodox is how I get from the roof to the wire for the grounding system, namely using the gutters and downspouts. As I said, the weak link is the small 2" strap from the roof to the gutter. The 6" gutter is the equivalent of a 9" strap, the downspout the equivalent of a 12 inch strap.

The ground system was there for the AC/telco/low voltage anyway. So for me the question/dilemma was is there something I can do that is better than nothing, even if it may not be as good as a full blown system. Much like a tower with a ground wire off each leg, the roof has ground connections at all four corners and in the middle (it's a shed roof). So for me doing the work and taking the liability, this was a good idea. The liability if anyone else does it makes it such that I can not recommend it, it's a SWAG system, and I've said so in my post.
In other environments, such as stuff I've installed at a tower site, I go 100% by the book and the cost shows it. The right copper strap and fittings, solid copper ground panels, all AC wiring in metal conduit, single point entry into the building, etc. If I was doing this for a living, I'd go 100% by the book so that I had no liability issues.

Thanks for pointers to those sites for those who are not in a position to make the trade offs on their own.

Pete

 

[pat32rf]

From what I remember of our physics class is that during a storm, the roof of your house, trees, barn etc build up a charge that is opposite the charge in the sky. When the charges are great enough you get a lightning "strike". Lightning rods are pointed because the electrons flow easier from a point than a flat surface. In a complete system you will bond those rods to the ground, not with downspouts but with copper wire. If you do things right the rods will bleed off the charge before a major strike occurs. This means that even a #10 or #8 wire can protect your building by stopping a hit. IF you are hit, then a #8 wire would vaporize.

When I was in high school we lived in a two story home in a field just outside Toronto. My bedroom was upstairs and I would listen to late night AM radio using a 15' antenna on the peak. On some nights I could draw a spark an inch long between the radio ground and antenna. When all connections were in place there was a 1/4" air gap and I would lay in bed listening to the spark jumping this gap every few minutes as the charge on the antenna built up.

Fast forward 40 years to a house my BIL built. The subject of lightning rods came up so I want searching for local suppliers. Nada. Neither the local farm co-op nor the TSC stores had anything, claiming they were no longer used in our area although we still ground our TV co-ax ...