That ground rod is only needed to carry that hundreds of amps for a split second*, until the breaker trips or the lighting strike is over.
*Or a few seconds as a worst case senerio.Thank You, Randy
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If you have ever seen the results of an actual lightening strike you wouldn't be quite so casual about the amount of current the ground circuit is required to carry.
Now, if you are talking about "static grounds" as used on airfields or around fuel storage systems that is a totally different proposition.
Bruce-in-Bangkok (correct Address is bpaige125atgmaildotcom)
On Fri, 02 May 2008 16:56:08 +0700, Bruce in Bangkok
Lightning events do have high-frequency content so skin effect does come into play. But you're right, .0005" of copper won't make much difference.
Consider that even steel has far higher conductivity than the earth into which it's driven. Making a ground rod more conductive than steel would serve no useful purpose. A better course for low-Z ground is to use more ground rods, because surface area is what determines effectiveness.
The diameter can be smaller and resistance can be higher than the cables coming out of a welder because it only handles high current during very short transient events, and even tens of volts of drop are acceptable during lightning transients.
Residential utility ground current should be very low, well under an amp and more like milliamps. There is a substantial neutral wire running back to the pole transformer. The reason for a groud reference is to prevent the system from attaining a common-mode voltage significantly above ground potential --e.g., 120 volts line to neutral but neutral is 400 volts above ground due to static buildup somewhere so the terminal voltages w.r.t. gnd are 400 and 520. Zap! Copper is a better choice for corrosion protection because zinc is very vulnerable to even weak acids. Slightly acidic soil would eat the zinc off a galvanized steel rod rather quickly.
I informed them when I did the work that it may not pass. I have no idea why they didn't just come out from the concrete and pound them in.
Steve
In my brain, a ground rod is for emergency path of current, and not a constant flow.
What do I win?
Am I right?
Steve
Skin effect is important at 60 hz. too. I forget the exact figure but as I remember at 60 hz it is not worth making conductors over 4 inch in diameter.
Recently saw a house with lightning rods where the wire to ground was Litz wire.
Dan
You could get a better conduction path by stringing a bare copper wire (say
8 ga.) next to the steel rod, than by plating the rod. 'course, that doesn't provide any corrosion protection, but my point is that doesn't do anything for you electrically. As far as a lightning strike is concerned, the current is enormous, producing a voltage drop so high that lightning may even jump LATERALLY from a tree trunk to a person standing under the tree. In order to get to the ground rod, the current will have traveled from the roof somewhere, probably along several paths.I believe that the ground rod is mainly there to establish that the house neutral is not floating, as Don Foreman said (more eloquently.)
The problem with the discussion is that there are a number of different types of "grounds". One, for example, the "static ground" is designed to dissipate static electricity to avoid igniting fuel during a re-fueling operation. It has been many years since I worked on that type of system but if I remember correctly the resistance can be in the 1,000's of ohms.
Then we have the grounds used with lightening rod systems that may be required to carry Mega, or Giga-amps of current.
Then there are the ground systems for radio antenna systems and grounds for safety (and maybe even grounds for grounds :-).
What kind of ground are we talking about.
Bruce-in-Bangkok (correct Address is bpaige125atgmaildotcom)
Copper clad ground rods have about 0.015" layer of copper on the base steel rod - at least the cutoffs I have downstairs are this way (cut off because of the mushrooming from driving interferes with the Cadweld mold) Gerry :-)} London, Canada
No, since the very or extremely thin layer might explode or vaporize. It acts as a fuse.
The sold ones are more than a e.t.l. of metal. The measure would be in so many circular mils of metal. Acting like a solid wire that melts. The steel acts as a strong holder for a conductor.
I've consulted with about 8 or 9 power companies and two are huge in size.
Martin
Mart> >
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Actually Ed is not far off but missed himself.
Current density for all points on a cross section of A is j=i/A
However since the resistivity of material varies greatly, the current flows in the copper.
The skin is the thin plating on the steel rod that every house has pounded into the ground near the power meter.
What messes up the even density in a solid copper rod (we don't have) is that of the electromagnetic field that drives the current outward. So the real density is loaded at the outer edges and this process really takes place in massive form in RF.
TV's are fed by an antenna. The antenna is fed by a air core coax. The central wire is a tube. No reason for using copper that electrons won't go. This makes the coax a little more flexible.
28 cycles that was intended to be used on Navy ships - with large iron transformers acting as ballast actually tunnels to the center of the conductor. An arm placed across two power posts will have the marrow burnt out. The Navy aborted the experiments.Martin
Mart>> >>
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In my case, a ground rod required next to the incoming 500Amp (large building) electrical service.
Steve
Because they would create a tripping hazard, and you are not supposed to have a ground like that right in front of the panel where you would make contact while resetting a breaker.
Simple solution - bury the conduit to the ground rod off to one side a few feet, and put the clamp below grade in a plastic or concrete handhole. You can order it with "Ground Rod" on the cover.
And if they ever pave the area, they just raise the handhole up a bit to sit at finished grade, and then it's always accessible.
NOTE: On new homes they just make a "UFER Ground" bond to the steel in the footing. Much neater, as it's all hidden in the wall.
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Just had a talk with an Australian "Sparky", a licensed professional electrician for probably 50 years. He tells me that according to Australian code the ground to any building entrance (I'm using U.S. terminology here) is the same size wire according to Australian code. He gave me the wire code but as it is not AWG or metric I have no idea what the actual size is, other then he said it was larger then normal wiring in the building.
Bruce-in-Bangkok (correct Address is bpaige125atgmaildotcom)
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