Per snipped-for-privacy@optonline.net:
Given that one of the building's grounds is a cold water pipe, it sounds like attaching that antenna ground wire to the nearest cold water pipe would do the trick.
Or would I be trying to electrocute anybody who happened tb using a faucet at the time of the strike?
I agree again.
The NEC wants a 20 ft max ground wire from the coax entry ground block to the power earthing system. If the wire is over 20 ft the NEC wants a ground rod near the coax entry point (connected to the entry ground block) and a #6 min bond wire from that ground rod to the power earthing system.
During an "event" that rod can be thousands of volts different from the building 'ground'. Because of the inductance of the bond wire and relatively high frequency current components of a surge, the bond wire does not necessarily reduce the voltage to a reasonable level.
IMHO the 20 ft limit is more reasonable for cable, where you have significant risk of surge entry. There should be little surge risk from a TV antenna. (The protection in the NEC is not for a direct lightning strike to the antenna - far more elaborate protection would be required.)
1 I might use a ground wire somewhat longer than 20 ft2 If a rod is added at the cable entry you could run the coax near the power service and add a second ground block. (That adds coax length and signal loss.)
3 Just add a rod and bond wire.Particularly for 1 and 3 (or leaving it the way it is) a plug-in protector at the TV would add protection. The coax must run through the protector. (All external wires go through the protector, and all interconnected equipment connects to the same protector.)
Here are my concerns with that approach. You have an antenna mast up on the roof with a ground wire that leads back into the house and is connected to a cold water pipe. Lightning hits the antenna and where are you asking it to go? Into the house. Don't know about you, but I'd prefer to keep it out of the house. And the longer the path from the antenna to earth ground, the higher the impedance. Also adding to the impedance are any turns the ground wire and piping make on their way through the house. If you have a couple 90 deg, sharp turns where the ground enters the house on it's way to the water pipe, there is the distinct possibility that the lightning will decide there is an easier path to ground and go that route. For example, it could just arc over to earth near where it enters the house. Again, I'm sure you can find plenty of houses where this has been done with no ill effects.
An interesting alternate method would be to have a ground rod for the antenna and then use the cold water pipe to bond it to the main grounding system of the house. That way with a strike, the vast majority of the energy is going to go right to earth, not into the house. By having that ground rod bonded to the other system via the cold water pipe, it would keep the ground voltage level close, ie the two will be at somewhat similar levels. Without it, you could have the ground reference at the antenna point thousands of volts different from the main house ground. And then the TV for example, could get damaged.
But I don't know if it's kosher to use the cold water system to do the bonding. I could sleep OK if it were my house, but technically I suspect something in the code says you have to run an actual grounding conductor between the two ground rods. Perhaps Bud can weigh in on this.
Per snipped-for-privacy@optonline.net:
Sounds to me like there is no downside to a dedicated grounding rod for the antenna - right under it where the ground wire drops down the side of the house.... and then work out the bonding possibilities with the rest of the ground system later.
Have I got it right?
The only downside is that later in many cases never happens. And until it is bonded to the house grounding system, with a lightning strike, you could have that ground and anything connected to it, ie TV, at possibly thousands of volts higher than the house ground, thereby destroying the TV, etc.
However, there are undoubtly a whole lot of houses out there where it's done with just the antenna grounded and no bonding. And given how much of a PIA it might be to run a proper bond, I might not do it myself either. At the end of the day, with what you describe, you don't have the perfect situation, but you do have a ground for the antenna and IMO it's not a big safety issue. More of an issue that the TV has a higher possibility of getting zapped.
The downside is that for a near strike, or strong surge current earthed through the power earthing system, the rod can be thousands of volts different from the building "ground". Those thousands of volts can show up at anything connected to the antenna and power. I wouldn't add a ground rod without bonding it back to the electrical system. But bonding does NOT eliminate this problem, created by the distant rod. IMHO the rod increases the probability of damage.
What the NEC wants now is the power system earthing connection to the water pipe within 5 ft of where the water pipe enters the house. One of the places for the rod bond to connect is in the same 5 ft. Years ago the power system connection could be anywhere on the water pipe. My preference generally is to connect the rod bond near the power service.
If lightning strikes the antenna, a ground rod will help only a little. The earth potential at the ground rod will likely be many tens of thousands of volts different from the building earthing and the building "ground". The antenna will be even further. There will likely be major damage. That can include arcing from the antenna or antenna wires to elsewhere in or on the house.
Ask a ham with a high antenna what you have to do for lightning protection. Earthing is only part of the protection. A major element is that all wiring rises to the same potential during a strike. You can't reliably do that with the distant (but bonded) rod. A start would be to route the antenna wire into the house adjacent to the power entrance with the antenna in a compatible location.
For most of us, it is real unlikely our houses (or antennas that don't stick way above the house) will be hit by lightning, and is not cost-effective to provide lighting protection.
Some principles: I isn't easy to make connection to the earth. A ground rod is one of the worst ways.
Two points of earth that are pretty close together can be many thousands of volts different during an "event".
The ends of a wire, maybe 20 ft long, can be thousands of volts different during an "event".
Per snipped-for-privacy@optonline.net:
But no higher than now with no ground rod at all, right?
Your observation about bonding later never happening rings true...
A local mechanic claims there is nothing more permanent than temporary.
Yes, I would think the possiblility of the TV getting zapped would be lower, not higher. If it were me, I would rather have the antenna grounded to a seperate ground rod that is not bonded to the main house ground, rather than no ground at all. At least you have a path for the main lightning current to follow and it's not into the house. In addition to the mast being grounded, there should be a lightning arrestor installed on the signal cable.
If I wanted to learn more about all this, what would I read. Preferably something that didn't simply say what the code demanded, but rather something that *explained* enough so that you'd be able to look at various grounding systems and be able to tell the pros and cons of each.
Any ideas?
David
Various? The code is the code.
Use GFCIs.
The grounding chapter of the NEC is likely the most confusing of the commonly used chapters. I have accumulated information over many years.
The best source may be "Soares book on gounding and bonding" published by the International Association of Electrical Inspectors. At almost 400 pages it is overkill for most people.
I read a book on "grounding" from the library and took strong exception to several pieces.
You can ask questions here, but sometimes it is hard to know what to ask.
It's unlikely w/o much detailed study and more background than you'll get you'll be able to discern "pros and cons" other than what is outlined for some given situation by any particular author.
An overall practical non-journeyman's guide is
It's based on given revision of NEC but is written as narrative-style rather than simply the Code sections and has introductory chapters that are good for getting concepts for the neophyte/non-engineer/non-techschool trained...you'll not be ready for licensing exam but you'll have a good start and have info at hand for most household/farmstead/_light_ manufacturing that likely to run across outside actual commercial/industrial applications.
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Dont forget to install a ground jumper between the 2 sides of the water meter, meters dont make good conductors and might be removed at some time.
And bond all grounds together. otherwise ground loops can occur.
Having grounds at different potentials can cause a hazard if anyone gets across 2 different potential ones. Nasty shock can occur:(
Excellent "white paper" on grounding and the neutral-wire here:
Hey, anyone go look at that stuff?
They have a variety of interesting "white papers" there.
If you have looked at any of it, how about commenting back here, suggesting that others do or do not go there themselves.
David
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