Call a lighting protection company. This IS NOT a DIY job!!!!!!

EVERY lightning protection has to be custom designed to the site and structure. You need to call an expert on this one.

If you haven't poured the foundation yet, one thing I'd suggest is to engage someone with lightening protection expertise early on.

Your house may (or may not) be a good candidate for a "ufer" grounding system, with the structural steel doubling as grounding electrodes encased in the concrete.

It's something that isn't inordinately difficult or expensive when the foundation design and specs are coordinated with the electrical design, but it's almost impossible to do "after the fact".

it MUST be bonded to teh house electrical ground. most folks mistakenly think that lightning protection is seperate from house ground, when in reality a PROPER job ties EVERYTHING together. how this is done depends on soil type, building materials, service type, lightning zone(believe it or not they exist) etc.

my latest lightning protection manul is a little over 500 pages worth of info, no way i could post it here!

I am a lightning protection designer and may be able to answer some of your questions if you still need assistance.

Tex- Yea, I'm mainly wondering if one row on the peak is sufficient - approx price, grounding, etc. When I have my foundation dug, do I need to add something for the grounding?

John

Are there any insurance issues here if the system is not UL certified and labeled?

Hi,

Lighting protection is best installed before you home is finished. You can hide more of the copper wires that way behind siding and in walls etc.

As for where you place the conductors consider a big sphere with a radius of 46 meters. Roll this all over the house. You want the sphere never to touch the house but to touch lighting conductors. Place rods accordingly.

However having said that you probably want to get some professionals in. Hooking up the the copper wire and installation has some subtle but important issues. For example no copper wire can bend more than a 6 inch radius circle or something like that. The idea here is that a sharp bend will tend to make the lightning bolt jump free of the copper conductor and strike somewhere else. Also the number of grounds you require and where they are positioned is also important.

Check out Wikipedia, there is something on this stuff there. I had an installation done two years back. 11 rods on the roof was about $US 9,000 I think. I am in New York State.

Best, Mike.

"You can hide more of the copper wires that way behind siding and in walls etc."

And if you ever actually have a direct strike set the place on fire.

Lightning arrestor down wires should always be on the outside of the structure.

Why would you even consider inviting 10,000+ amps into you building?

Hi,

Brickeye is probablly right about hiding wires etc. The installers when they came said that the could hide it. How and the details of how I do not know. What they said was if you install at building time, from the ground looking at the building you would not be able to see the copper wires because they could hide them...

Best, Mike.

Personally, I think the best "lightning protection" is a comprehensive homeowner's insurance policy. I do not trust an electrode mounted 6 inches from my roof to divert a strike that may have traveled over a mile in open air already.

You can hide lightning rod down wires behind downspouts.

Putting them in downspouts or metallic tubing is NOT a good idea.

The metal enclosure acts as a shorted turn to the magnetic field and alters the impedance.

John, the placement of air terminals, or lightning rods on the roof depends on the pitch and span of the roof. Lightning protection codes allow that a roof with a pitch of 3:12 or greater to have protection at the ridge lines only. However, if the span of the roof (distance from eave to eave) is 40 feet or less, than that pitch need only be 1.5:12 in order to protect the ridge only. If the span is greater than 40' but the pitch is less than 3:12, then protection must, by code requirements, have air terminals along the perimeter and in mid-roof spans 50 feet on center. There is actually more to it than that, but most homes have roof pitches greater than 3:12, so this should not be an issue. In addition, don't listen to anyone telling you that concealing the conductors within the wall cavities and attic space will burn your house down. Very untrue. In fact, most professionally installed lightning protection systems are "concealed" systems. Usually the only time a system is exposed is if the structure is existing and concealing the system is just not possible or cost beneficial. Either way, if you have any further question, please feel free to ask.

P.S. Sorry for the late response, I have been out of town without access to the internet.

A few more issues after reading some of the posts above. If you are considering an exposed system, you actually can semi-conceal the down conductors from the roof to ground behind downspouts, but codes do not allow to attach the down conductors to the downspouts or route them through the downspouts. Also, I read that some one had posted that the max conductor bend being 6" radius. It is actually 8" radius and a turn of no less than 90 degrees. Codes require that all conductor maintain and horizontal or downward coursing to avoid what is called a "U-pocket" in the conductor. As far as cost goes, it just depends on the size of the house and the amount of material required. It would serve you well to get an estimate from a lightning protection company. Most lightning protection companies offer cost free estimates. again, if you need any further assistance, just let me know. Thanks.

Texorcist- My pitch is 7:12 and 10:12. House is around 40' x 80', ridge is approx 50' long. Approx how many would I need along the ridge - 4 or 5 with each around 2' tall? I will not install myself, just looking for some info before I start asking contractors about it.

Thanks, John

John--

When protecting your ridge, lightning protection codes require that the air terminals be located within 24" of the ridge ends and spaced every 20' apart along the ridge, or fraction thereof. So, you would only need 4 air terminals spaced evenly along the ridge with the end air terminals located within 24" of the ridge ends. Codes only require that the air terminal be 10" above the object(s) that are being protected, which in this case is your ridge. Therefore, the air terminals can be only 10" and be code compliant. Unless your roof is standing seam metal, in which case I would recommend using 12" air terminals to ensure that the air terminals are 10" above the seams. But I assume that your roof is the typical composition shingle.

Hope this information helps. Let me know if you have any other concerns.

Steve

Texorcist can probably anwswer this or correct my error, but I thought that the purpose of air terminals and the grounding wire was to "bleed" off charges (can't remember if it's neg or pos ) that build up on a structure that make it likely for a lightning strike to occur, rather than to actually conduct a strike to ground. So, their main purpose is to make it less likely that the structure will attract a strike in the first place, but also providing a path to ground should such an event occur. As to the likelyhood of a fire from hidden cable, I'd suspect you'd be a whole lot more likely to get a fire if your house is struck with out protection. I used to date a girl whose father sold lightning protection and he had a pretty incredible scrap book of damage that it had caused. It was a pretty good persuader.

No one has a definitive answer for the 'bleeding charge' vs. 'diverting strike' argument.

The fact that tall buildings are very well grounded yet are struck repeatedly seems to indicate that the bleeding charge argument does not work very well.

Aerial heights are set based on the protected cone they provide.
A cone with the tip located at the top of the aerial and extending downwards with a 90 degree included angle is used to determine the zone.
Lightning is very unlikely to strike within this zone since the aerial provides a much lower impedance path to earth.

Turns in the down wires should have as large a radius as possible.
The magnetic field from the current flowing becomes crowded on the inside of the bend. This increases the impedance and can result in the current leaving the down wire for a lower impedance path.

Even with a rod system, you can expect to loose some electronics for a direct, or even nearby strike.
Anything with wires over a few inches long will act as an antenna and couple both the electric field and the magnetic field from the strike.
This produces high voltages in whatever the wire is connected to.
If you have a strike, you may need to have electrical wiring checked for damage, including megger test for insulation damage in concealed wiring.

We used to be able to easily tell if our office building or an adjacent one took a hit.
All the CRT monitors would jiggle the image as the current flowed through the building to earth.
If it hit the building beside ours it was just as loud, but not enough field in our building to disturb the monitors.

I had an office with a wall against the lift well, and when the elevator (or counterweight, never knew which) passed behind the wall, the crt image would wiggle. Either it was just the mass of iron (counterweight) itself, the elevator electric cables, or the elevator itself. Could also be that the counterweights were magnetised by the movement itself, although I would have thought magnetisation by movement in the earth's magnetic field would be more likely in an horizontal motion, rather than vertical.

Still it was an odd (and annoying) phenomenon.

The main purpose of a lightning protection system is to provide the lightning with a path of least resistance to ground. A faraday cage system, or typical lightning rod system, neither repels or "bleeds" off lightning nor does it attract a lightning strike. It's sole purpose is to provide the strike with these low resistance paths to ground in order to prevent structural damage. This, coupled with proper surge arresters at the electrical service entrance and a TVSS system will greatly reduce change of damage to a structure and it's electrical components.

FYI, the "zone of protection" is calculated using a formula based on a 150' radius "rolling sphere" as outlined in UL96A, LPI 175 and NFPA 780.

"I had an office with a wall against the lift well, and when the elevator (or counterweight, never knew which) passed behind the wall, the crt image would wiggle. Either it was just the mass of iron (counterweight) itself, the elevator electric cables, or the elevator itself. Could also be that the counterweights were magnetised by the movement itself, although I would have thought magnetisation by movement in the earth's magnetic field would be more likely in an horizontal motion, rather than vertical."

The counterweight is magnetized, likely by accident.

It may have been cooled when cast in a strong magnetic field, it may have been handled with a magnetic pick up, or it may have been near a large current carrying wire that was suddenly turned off.

Any time a field is present and then quickly interrupted
ferromagnetic materials can be left with a residual field.

"A faraday cage system, or typical lightning rod system, neither repels or "bleeds" off lightning nor does it attract a lightning strike."

Care to walk around holding a metal pole during a lightning storm and investigate?

A lightning rod attracts lightning that comes near.
It does not cause the strike, but since it represents a lower impedance path any nearby strike will preferentially take the lower impedance path.

The danger in standing under a tree during a lightning storm is that you are a far better conductor than the water in the tree.

If the tree is hit the current flows under the bark in the wet cambium towards the earth.
If you are near the base of the tree the current will seek out the lower impedance path through your body to earth.

Did you 'attract the lightning'?

Not in the sense of it hitting the tree, but once it got near you in the cambium layer you DID attract the strike since you are a lower impedance path.

I guess I had misunderstood the "bleeding off" a charge as "repelling" and lightning charge. And yes, obviously an air terminal "attracts" lightning in the sense that it is a path of lower impedence, but what I was referring to is that it does not attact lightning in the sense that it causes a structure to be struck. Guess I should have been more clear.

The bleeding off theory has been around for as long as lightning rods.
It is based on the displacement currents that travel under a charged cloud in the earth.
The theory is that the rod acts to help dissipate the charged cloud before a breakdown and a strike occur.

It is not "repelling" the bolt, but may help reduce the potential between the earth and the charged cloud.
Currents can be measured in the down leads of systems even when a strike has not actually occurred, so there is some indication that charge us moving into the air.

An air terminal will attract a bolt that is in proximity.
The problem is that there is no way to know if the strike would have hit the structure anyway.