Lightning Rods

[upstatemike]

After the recent storms I am reviewing all of my UPS and surge protector strategies and I also decided to inspect the condition of my lightning rods and associated cables since they don't get much attention most of the time. I also started paying attention to the lightning rods on my neighbors houses as well as those on commercial buildings down in the city, and I noticed something that I never realized before. Most recently constructed houses do not appear to have lightning rods at all. All of the older houses in the area have them and all commercial construction, old and new, has them but none of the newer houses do. Does anybody know if there is some change in residential contruction techniques that reduces the need for lightning rods? Is it because some houses are built without fireplaces and don't have chimneys?

I see some people talking about building new houses and discussing "whole-house surge protectors" and other storm protection measures and was curious how lightning rods figured into their overall construction plans?

 

[pete]

just started looking into this and found this at National Lighning Saftey Institute

Since Franklin's day lightning rods have been installed upon ordinary structures as sacrificial attachment points, intending to conduct direct flashes to earth. This integral air terminal design does not provide protection for electronics, explosives, or people inside modern structures. Inductive and capacitive coupling (transfer impedance) from lightning-energized conductors can result in significant voltages and currents on interior power, signal, and other conductors.

and on a differnt page

If lightning strikes a LPS on a structure, it is possible that transfer impedance (see IEEE 1100-1999 Powering and Grounding Electronic Equipment, pp. 61-78) may energize unintended conductors listed above. The magnetic effects of lightning also may couple to these unintended conductors. Casualties to people inside modern structures typically include: while on telephone; while in bath or shower; while washing at kitchen sink; while touching electrical appliance; while touching or near metal door or window. (Benj. Franklin suggested safety while inside could be obtained by lying in a silk hammock slung in the middle of the house.) According to an insurance study (Gugenbauer A., Linz Fire Protection Authority for Upper Austria) indirect vs direct lightning damage is about 100:1. This means that the LPS is of no merit in cases of indirect lightning strikes nearby to but not on the structure. NLSI suggests that detailed attention to bonding, grounding, and surge protection ranks higher in priority than the LPS.

just some info for your perusal . . .

 

[jrfuda]

I recently saw an episode of Myth Busters where they played around with some of the lightning myths - well they turned-out to not be myths.

They used a dummy made out of ballistics gel to see if it would get a lethal dose of electricity while doing things such as using the phone or taking a shower during a simulated lightning strike. What was funny was that the lethal lightning strikes did not hurt the electronic devices (they had an old PC and TV connected to the mains of the "house" they built to conduct the tests.

I find that 100:1 indirect-to-direct hit ration interesting, and between what some of y'all have posted and I've had friends and family experience, it's probably even worse... I bet only a handful of the indirect hits ever get reported to the insurance company, whereas close to 100% do get reported, so I bet it's more like 1000:1.

My sister-in-law lost equipment on THREE different occasions in a 6-month window due to indirect strikes (and probably due to the wacky way their 1930's-built house is wired)

 

[AutomatedOutlet]

John,

I saw that episode too and don't think that their testing methods were valid. They had metal objects way too close to each other in their mocked up test house that they built. In reality, I really don't think houses are built like that.....

 

[upstatemike]

Since Franklin's day lightning rods have been installed upon ordinary structures as sacrificial attachment points, intending to conduct direct flashes to earth. This integral air terminal design does not provide protection for electronics, explosives, or people inside modern structures. Inductive and capacitive coupling (transfer impedance) from lightning-energized conductors can result in significant voltages and currents on interior power, signal, and other conductors.

I agree that conducting direct flashes will not protect electronics but conducting direct flashes is only the secondary role of an LPS, and is meant to prevent fires and other physical damage.

The primary role of an LPS system is to reduce the likelyhood of a direct strike. The intense electric fields surrounding a pointed object serve to ionize the surrounding air, thus enhancing its conductive ability. (That is why lightning rods have such sharp points) As a storm cloud approaches, there is a conductive pathway established between the statically charged cloud and the lightning rod. Static charges gradually migrate along this pathway to the ground, thus reducing the likelihood of a sudden and explosive discharge. Thus, the primary role of a lightning rod is to discharge the cloud over a longer length of time, thus preventing the excessive charge buildup which is characteristic of a lightning strike. (paraphrased from the explaination on this page ).

Reducing the likelyhood of of a direct strike definitely CAN protect your electronics.

In any case I already have lightning rods so I have ordered serial port surge protectors and series mode AC surge protectors from here and here.

 

[compuguru]

I also saw that episode of MythBusters. I seem to remember that they had to remove the ground wire to get the shocks that they wanted.

 

[AutomatedOutlet]

Yeah, the whole thing was rigged I think to get the shocking results they wanted. Image, on that show, they "Proved" that it's dangerous to take a shower during a thunderstorm. Come on, give me a break! <_<

 

[jrfuda]

Come on guys, I always talk on the phone with a packet of gunpowder strapped to the receiver in an ungrounded house, don't you?

The more I think about I think they actually did "bust" the myth, rather tan confirm it or label it "plausible." I think all the stuff we saw later was them going the extra step to make the myth occur, like when they strapped C4 to the air tank in their Jaws mockup for the shark week episode.

Anyway, it's entertainment, and since it's on the Discovery channel, I can lie to myself about being smart becuase I'm watching it. If I really wanted to impress myself with my intellegence, I'd have to put on PBS <_<

 

[AutomatedOutlet]

I enjoy watching that show too but on that episode, I think that they were saying that that myth was TRUE. I just don't believe it though.

 

[Chas821]

Having been involved with electronics and various equipment during my military career AND inspecting said equipment (including proper grounding) let me say that if you think your house's electrical system is properly grounded, think again!

Most electrical contractors drive a 8 foot copper-clad rod in the ground close to the service entrance (where the meter is) and attach the gound wire without regard to proper bonding techniques. Many times the attaching clamp loosens over time and the wire is so loose you might as well not have a ground. Add in the corrosion effects over time and you start getting the idea. Even properly installed grounds can have problems if you have very sandy\rocky soil. Conduction requires the ground to have a certain amount of moisture and if you have soil that dries out, there goes your ground. You best bet is to inspect the installed grounding system and ensure you're protected at least that much.


Chuck

 

[upstatemike]

Having been involved with electronics and various equipment during my military career AND inspecting said equipment (including proper grounding) let me say that if you think your house's electrical system is properly grounded, think again!

Chas821-

I think this is a point worth looking into! Do you have any links that talk about proper grounding and bonding methods?

 

[jrfuda]

Here's an old post about grounding: http://www.cocoontech.com/index.php?showtopic=1423

And a link from that post: http://www.selfhelpandmore.com/homewiringu...etershow.htm#16

 

[Chas821]

upstatemike,

Your best source for this information is the local library where you can look at "the" book, the National Electrical Code. There are many references on the net as well. Just google "grounding practices" or "grounding and bonding".

Good luck!


Chuck