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Old 07-30-2009, 09:23 AM   #21
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Rich, I guess this is the definition if mixed feelings - unexpected expensive repairs to the home but it could have been much worse.

A whole home lightning arrestor is designed to block an incoming surge, like strike close by on a tree – but even the best can’t do anything for a surge that already hit inside the home. Even combined with individual surge protectors for the pricier appliances and electronics, once the excess current reaches the inside wiring anything goes.

I wonder how to protect against this. This is how my home is set up and I never thought about this possibility, live in south florida with lots of lightning and a fair amount of expensive electronics (and already spent a bundle on lightning arrestor and surge protectors).
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Old 07-30-2009, 10:53 AM   #22
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Nothing is going to protect against a direct (or very nearby) hit. The whole house protectors can help if the hit is not so direct.

Think about it - think about the power in a lightening strike, and how fast it occurs. What is anything that you connect to your breaker box going to do to contain that much energy? And how much damage is going to get done as the energy travels between the lightening strike and that box? Where is it going to dissipate it? You just cannot deal with an outburst like that.

Even if you made a really fantastic effort to absorb that much energy that quick, the energy is finding parallel paths to take. It's probably about equivalent to having your seat belt on and hitting a brick wall at 120mph. The force is just too great, and too many other paths for the energy to take to kill you. The seat belt will help at lower speeds, but there is a limit.

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Old 07-30-2009, 11:34 AM   #23
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Ahem.... The purpose of lightning rods is to provide a continuous discharge path to ground. By discharging the area in the vicinity of the roof mounted spikes, in theory at least, the lightning will find other locations to wreak havoc.

No residential type lightning rod/grounding can handle the power of direct strike.

Typically tall and not so tall antenna structures have good grounding. Between antenna cable jackets and ground in good installations there is a loop in the cable and a spark gap of a 1/4" or so which allows high induced voltages to jump the gap to ground and then the rest of the overvoltage protection systems can do their thing.

The loop and spark gap is usually at the base of the tower and another outside of the structure where cables have their entry ports.

OTOH if the lightning discharge is fairly close to the lightning rods, the grounding network and cables leading to the pointy rods help move opposite polarity charges up to the tip of rods and well beyond. Typically around 100' or so above the points. Then the lightning is sort of neutralized at a height of 100' or so above the structure. Thus mitigating damage.

Then of course there are the real big'uns. Hope for the best.
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Old 07-30-2009, 12:02 PM   #24
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Ahem.... The purpose of lightning rods is to provide a continuous discharge path to ground. By discharging the area in the vicinity of the roof mounted spikes, in theory at least, the lightning will find other locations to wreak havoc.

No residential type lightning rod/grounding can handle the power of direct strike.

Typically tall and not so tall antenna structures have good grounding. Between antenna cable jackets and ground in good installations there is a loop in the cable and a spark gap of a 1/4" or so which allows high induced voltages to jump the gap to ground and then the rest of the overvoltage protection systems can do their thing.

The loop and spark gap is usually at the base of the tower and another outside of the structure where cables have their entry ports.

OTOH if the lightning discharge is fairly close to the lightning rods, the grounding network and cables leading to the pointy rods help move opposite polarity charges up to the tip of rods and well beyond. Typically around 100' or so above the points. Then the lightning is sort of neutralized at a height of 100' or so above the structure. Thus mitigating damage.

Then of course there are the real big'uns. Hope for the best.
OK, got it. So is the bottom line in your estimate that residential lightning rods and/or surge protectors are a highly hit or miss solution that will likely not provide protection in many if not most of the scenarios you mght encounter?
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Old 07-30-2009, 12:37 PM   #25
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Right.

Now if you can convince your neighbor that it is useful, it'll provide about a 150' somewhat protective radius from the nearest rod.

To do it correctly for an existing structure, it is a lot of digging for the underground ground cables. Likely $$$$. Not to mention the upheaval of existing landscaping. Without them the the pointy rods on the roof are useless.

Edit add: Surge protector are good up to a point. I have one from HomeDepot at the service panel and another one at a sub panel next to my electric dryer plug. I think they are about 50 bucks ea.. They tend to work best singly when installed at a high load circuit furthest from the service entrance (like an electric Dryer plug)
Most harm comes from power lines are brownouts, AKA voltage sags during high demand times ie. 95 volts or below, tend to burn out motors. For residential purposes correcting for is cost prohibitive and inefficient (called constant voltage transformers) they make a lot of heat and noise.
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Old 07-30-2009, 02:23 PM   #26
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Edit add: Surge protector are good up to a point. I have one from HomeDepot at the service panel and another one at a sub panel next to my electric dryer plug. I think they are about 50 bucks ea.. They tend to work best singly when installed at a high load circuit furthest from the service entrance (like an electric Dryer plug)
Most harm comes from power lines are brownouts, AKA voltage sags during high demand times ie. 95 volts or below, tend to burn out motors. For residential purposes correcting for is cost prohibitive and inefficient (called constant voltage transformers) they make a lot of heat and noise.
My circuit tester/surge protector cuts all power when it drops below 104v. Why do motors not like low voltage? I can understand that they won't run properly, but what happens to damage the motor just because the voltage is low?

And how the heck did you learn all this? .
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Old 07-30-2009, 04:29 PM   #27
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Aha the $64k question.


Somewhat simplified: It has to do with the counter electromotive force generated by rotating machinery, ( motors can act as generators, though not very good at it) which limits the current in the windings

When running slow, less counter EMF is generated allowing much more current through the windings, plus the slower speed gives less cooling, ergo mucho heat, cooked wires.
Cooked wires(windings) let the magic smoke out of the motor and it dies.

As to how I learned? I was born curious, at age 6 already graduated to dis-assembling much my brother's motorcycle, this after pulling the film out of his Leica (pictures he traveled days to take) to look at the pictures. These acts nearly caused my demise at his hands, mother intervened, so I got to live.

In time after destroying many things I learned how they worked, eventually learned how to re-assemble.

Discovered electricity by dismantling the family radio, wanted to know what made the magic eye tuning indicator work. In the process the still charged filter capacitors discharged through my fingers, getting my attention.
This act nearly got my mother to finish me off, (radios cost 2 to 3 months vages back then, if you could get them at all) brother intervened, got live again. They recounted these things later in my adult life.

From there a lifetime of learning ensued, and still in the process. Formal education in the electric arena was as an electrician student back in the old country.

I still love to tinker, learn, and play with all sorts of gizmo's. But a lot of what I know is fast becoming obsolete.

Now in retrospect if I directed those energies to money making, I'd prolly be far richer, but not likely happier. Who knows?
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Old 07-30-2009, 07:52 PM   #28
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OK, got it. So is the bottom line in your estimate that residential lightning rods and/or surge protectors are a highly hit or miss solution that will likely not provide protection in many if not most of the scenarios you mght encounter?
The only advantage is that the next lightning bolt may be more attracted to your lightning rod than your A/C system.

Years ago Lee Trevino was struck by lightning during a golf tournament. Later he used to joke that next time he'd hold up a 1-iron. Why? Because not even God can hit a 1-iron... Maybe you could just tie a golf club to a high tree branch, clamp a wire to the shaft, and route the wire down to the ground.

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And how the heck did you learn all this? .
Six months of nuclear power school, six months at a shore nuclear plant, and 20 years of pouring various types of conductive fluids into heavy-duty circuit breakers experience...
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Old 07-30-2009, 11:53 PM   #29
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