I got a call from our monitoring station Wednesday night. The assisted living home I've been installing a number of low voltage systems in had taken a lightning strike, and they wanted me to get things in hand. I won't bother with the litany of evaporated components and troubleshooting hassles; suffice it to say the bill is probably pushing $14,000.00 so far, and I'm not done yet.
Surge protection? Plenty. Grounding? That's where my issue lies. All this has raised an old arguement that I have had, mostly with myself, about what grounding is really for, and I'm hoping the Fine elctrician(s) that read this missive will chime in.
I have maintained for some time now that grounding is to protect people, not equipment. In fact, with what little I've read on the behaviour of lightning, it seems grounding is usually the path that this terror takes on its way to your stuff. Illustration: Take a solid silver ground rod and drive it all the way to the planet's mantle. Wrap a 4AWG around it, clamp it and weld it to the rod, leaving a 6' long tail. Now, imagine there is tree 50' away that it is going to get hit by an average strike in 15 seconds. Are you willing to hold on to that tail? To me, common sense says that all that current is not going to take a 90 degree turn and head for China. Some of it is going to energize that tail, or your wiring system.
How am I doing?
Jeff

Sure, I'll hold on to the tail.


Grounding on buildings protects the building and the things inside it.
Grounding on equipment protects people handling that equipment.

Methinks a GOOD lightning rod system is in order here. I had to install one for a customer after he lost $12000 worth of amplifiers, subs, and plasmas...

Let's go a little further and pony up a description of system you installed. Perhaps we can $ell it on the next job.
Much obliged.
Jeff

I'll chime in a bit here:

No surge-protection device can guarantee protection of electrical and electronic equipment against a direct strike. The voltages and current are just too great, even with the typical short duration.

Lightning rods, now called "air terminals", are mainly meant to reduce lightning strikes, because they help "drain off" excess electrons from the ground up. The sharper the point on the rod, the more effective they are.

The secondary benefits of rods may help divert a portion of the current around the outside of a building, and may even reduce the liklihood of fire, but there will still be plenty of induced currents in any metal around.

Often, the nails in a house produce charring in the wood surrounding them, and they're not even part of a circuit. Imagine the induced currents in your house wiring, where one end of every circuit is grounded (the neutral).

The best TVSS setups use main-service voltage clamping cascaded with point-of-use secondary clamping combined with current-limiting for sensitive electronics. A certain portion of surges are generated within the building by other equipment.

In addition, every wire entering the premises should be grounded via a device with a voltage gap for each conductor, as well as directly grounding any shielding and metal (masts, dishes, etc.) Not easy to do, but important.

Finally, all grounding points should be interconnected (bonded). Remember, current requires a difference of potential (a.k.a., voltage), and bonding reduces potential differences. Unfortunately, that can lead to ground loops, but them's the breaks.

When lightning strikes (or high-current short circuits, a.k.a. ground faults or "bolted faults") occur, the extreme currents cause voltage drops along conductors, metal, and even the earth itself (called "gradients"). Bonding minimized these gradients.

Finally, while it's said that "electricity follows the path of least resistance", the truth is that electricity can have many parallel paths. Do your lights go out when you turn on the stove or A/C? Of course not! Same for lightning.

I could go on spouting for a while, but it's time for dinner. I hope some of this makes sense.

Larry
www.fineelectricco.com

Well stated Larry.

To carry it one step further, Lightning tends to behave like high frequency energy. It will follow the rules of nature and attempt to take the path of least resistance (or paths), but since inductive and capacitive reactance come into play with high frequencies, what appears the "least resistance path" to us will not necessarily be the actual path of "least IMPEDANCE" to the lightning bolt, and with anything but DC, it is the impedance of the circuit that matters, not just the actual DC resistance.

Larrys advice for grounding is very solid information.

Thanks to all. Larry, your explanation was all I expected it to be. At the risk of being presumptuous with your time, are the things that you mention (or any portion of them) the kind of thing you would expect as standard fare for a commercial structure? If not, how much of this should a commercial customer expect if he asks for surge protection on the whole building? Thanks again!
Jeff

Jeff, not to worry. I wouldn't be here if it wasn't fun!

There is no one answer; that's like asking what one should expect in a home theater. It's whatever is agreed upon between the parties involved, and who's footing the bill.

If it were my equipment, I'd be very picky. I wouldn't rely on someone who's priority is spending as little as possible meeting my requests. Remember, profit = income - outgo.

Larry
www.fineelectricco.com

Hmmm, well said. Delivers us from the lowest bidder...thanks again, Larry.
Jeff

Ooops; didn't mean to put the "s" on "deliver".
Jeff

Well, that's a pretty good pun. But I quote this for a whole other reason: please join me in trying to restore humanity to one little part of the English language; it is electricians WHO, not electricians THAT, as they are people.

Even Larry.

That is something I never thought of! And it is so true!


This means that, even if the breaker were open, you could end up with spikes of thousands of volts applied to the equipment!



Again, didn't we all think the voltages had to do with the way the lightning's energy spread out? The fact of induction is VERY important in this process.


Yes, but there is an interesting phenomenon that I noticed as electronic components evolved from audio only to audio plus video. You will have no hum when there are NO ground loops, as in "star" grounding of an audio-only component. You will have hum when there are a few ground loops, as in grounded cable plus a grounded plasma chassis. BUT if you have lots and lots of grounds, eventually the tendency to hum will go away because no single ground path will have enough current (and therefore voltage due to IR drop) to create hum. I have seen this in homes where the system hummed when half-wired, but was totally clean when finished, with no attention paid to ground loops until we were done...and then none was needed.


Electricity follows ALL paths that have less than infinite resistance, and the amount on any one path is strictly proportional to the resistance of that path. The above statement is only the most obvious one, but people have been killed by ignoring the reality of other paths.

It's so cool when someone really groks on one of my lengthier ramblings-on. As Ernie added, the multiple parallel ground paths eventually have such a low total impedance, the entire installation becomes a ground mat.

Note: Electrical sub-stations are constructed over a copper mesh in the ground, to which all metal parts, even the fencing, are bonded. The idea is to assure that the earth surrounding electrical equipment is at the same potential as the equipment itself, even if not at 0 volts.

A couple of years ago, we did the entire in-ground installation for a cellular site; 5/8" copper ground rods (14), ground ring (#2 tinned solid copper), ground-rod connections and everything metal bonded by exo-thermic-welded connections throughout, etc.

We learned a lot on that one!

Larry
www.fineelectricco.com

Ernie,
Thanks for the correction! That one would have gone forever unnoticed by the author. I will gladly join your effort. Grammer, syntax, spelling - all victims of widespread keyboarding with no schoolteachers watching over our shoulders. It's bad enough that "aggravate" became a synonym for "irritate"; now "peruse" is starting to mean "scan". This could be a long battle.
I also appreciate your contribution to the topic. I have noticed the effect of multiple grounds in the past. Never really knew why, though.
I can't help but think that you and Larry would make a formidable combination in this business. I guess we should be glad you're 3000 miles apart!
Jeff