(slightly OT) driving a ground rod
The soil here is mostly clay mixed with layers of shale. Driving an 8 foot ground rod is usually a real task. It is such a pain that sometimes an inspector will allow us to dig a trench and lay the rod horizontal.
The guy who installed my HughesNet dish for my internet showed me a neat trick. He suggested a hammer drill. I tried it yesterday.
My small drill did well until I hit the shale. Luckily I have a large Hilti hammer drill (TE72). It smacked that baby right through the sand stone and buried it in short order.
This may be old news for some of you but it was certainly a neat new trick for me.
SCOTT (fabricator - wanabee machinist)
Gounding is part of a good distribution system, so not slightly OT, very much on topic.
I"m not sure I understand the operation with the hammer drill. Do you chuck the ground rod into the hammer drill so it rotates as it hammers it in?
We used a jack hammer
Back in my millwright days we had a 125 pound air jack hammer with an adapter to drive ground rods. Had to be careful in rocky soil, the hammer would quickly make a pretzel out of the rod if the rod hit a big hard chunk of granite.
I use a hunk of steel or black iron pipe with a galvanized cap on one end, slide it over the rod and use its weight to drive it in. When the rod gets deep enough to where the pipe hits the ground, it's usually stiff enough to finish with a drilling sledge and a smaller pipe cap. Then I finish it off with a grinder to take off the inevitable mushroom head I create with all that pounding!
Note: don't use black iron caps, they shatter!
What is the resistance to ground of your ground rod in the clay-shale soil?
A 60 pound demo hammer works great.(it's a small jack hammer) They make a special bit for them just for this. Start by standing on a 6' ladder and then let the hammer walk it down. Most hammer drills are too light to really do the job, but if your roto-hammer has a hammer only position it might work, depends on soil. Out here we have often very hard soil call collechi(sp?) which is like concrete. If you don't hit that there are usually lots of rocks to deal with.
Oh yeah, ground rods make great divining rods.
By that I mean they are very good at "finding" buried treasures. Like conduits, water pipes, etc... And those must be treasures cause they sure cost a lot to fix! Be real sure what's under you before you drive one!
The installer that first told me about it just chucks a cut-off extension and a 5/8" socket. The rod doesn't rotate.
Originally Posted by ricdel
My Hilti drills use a dedicated bit, not a Jacobs style chuck. I cut off the shank of a worn out bit and welded it into an adapter sleeve I turned on the lathe (nothing fancy). It put the rod in great until I hit the rock. I got out the big drill (TE72). The ground rod actually just went up into the socket where the bit is supposed to go. I made sure it wasn't going to damage any check balls and poured it on. It went through the rock easily. To answer your question; fairly loose fit, no rotation, just thumpity thumpity.
Now I understand and I need to drive 2 ground rods . I will make up an adaptor for the sds drive on the hammer drill.
Why do you need two ground rods?
Because NEC art. 250.56 says if a driven rod,pipe,or plate electrode does not have a resistance of 25 ohms or less shall be augmented by 1 additional electrode of any of the types specified by 250.52 (A)(2) through (A)(7),and they need to be at least 6' apart.
Originally Posted by gar
It's cheaper to just drive 2 rods and call it good then spend some serious money on testing equipment to prove 25 ohms or less........
BTW, this first appeared in the 1999 NEC.
That makes good logical economic sense.
I was interested in knowing what your resistance was and the type of soil.
There are few if any places where you can get very low resistance. What do I mean by low, maybe 0.001 ohms or lower.
Without a lot of cost you can get an estimate of ground rod resistance with an ohmmeter. Assuming you have a copper pipe water supply to your building this can be used for one electrode of the test. Use the ohmmeter to measure the resistance from the ground rod to your water pipe.
Since the ohmmeter applies a DC voltage for the test a polarization effect takes place. If you quickly alternate the leads, maybe 2 to 4 times per second, you can mostly cancel this effect. A Simpson 260 or 270 meter is better for this than a digital meter.
Another method is to use an isolation transformer with a 25 to 30 V secondary of maybe 2 A rating. In series with the transformer output insert an AC ammeter and connect this output to the ground rod and the water line. Measure the voltage between the ground rod and the water line. Now an estimate of ground resistance is Rg = V/I. At 10 ohms and 30 V you can expect 3 A. If you are above the transformer rating do not leave connected long. This is not the same as the NEC specified multiterminal test, but it provides a reasonable estimate.
I have two different locations that I am changing the electrical service at.
The one building I am moving the service enterence to the other side of the building and running the wires underground.
Didn't mean to be confusing.
Most SDS/SDS-MAX drills... and on grounding challenges
Most manufacturers of SDS/SDS-MAX bits make rod-driving bits available off-the-shelf. I use one with my Milwaukee (SDS-MAX), my co-workers generally run the SDS, all have similar drive-cups.
Another handy tool, is the asphalt-chisel... great for chipping ice off of hard surfaces with the hammer-drill in hammer-only mode.
Another similar situation is driving large roll-pins and Spi-Rol pins. We used to use 5lb machinist's hammers and drifts. I ground the end of a broken chisel-bit to suit, and now use my air-hammer to drive 'em in... sure is easier to do, and I don't hit my hand, or other sensitive (pronounced expensive) objects driving pins into, or out-of things.
On the subject of poor ground conductance, if you have shallow rock, laying the rod flat typically provides better performance, as the rock rarely provides a good ground-conductance. Another method used by ham-radio guys, is to lay down a series of 'radials' in shallow trenches eminating outward from the grounding point, using heavy copper wire, and ground stakes (oftentimes, cut to half-lengths where shallow bedrock exists) at regular intervals. In radio, these radials perform several functions, but the end result comes out the same- an artificial 'ground' system creating a low-resistance path of dispersion where soil and ground conditions otherwise would not yield a reliable plane. Typically, a 'ring' of wire around the whole building is employed to which the 'primary ground' is connected. Unfortunately, I've found that many inspectors interpret this as violation of 'single point grounding', when it really isn't.
Im intrestd in your grounding comments. These grounding issues are too often ignored around my area by any variety of equipment installers. Good (effective) grounding is indeed important.
As a point of nit-pick, Im not certain, though, that the electrical phenomenon were trying to achieve in radio is the same as we are looking for in electrical work. The optimum size of the radio ground plane is a function of the antenna size. I wouldnt be offended to be corrected, however...
It's not nitpicking...
Some of the principles desired in a power-system grounding scheme are also used for radio transmission and receiving, however, there are several more principles required for good/safe/proper TX/RX that power distribution and energy management have no concern.
In a power transmission/distribution/control system, safety is the first concern- electrical shock, fire prevention, and equipment protection. To keep a good system, having a good method of passing electrostatic discharge (from wool socks to direct lightning) through a path which will also provide for the above.
While it is usually unknown or misunderstood by electricians, inspectors, and even engineers, a good design of the power system and grounding should also minimize undesired electromagnetic and electrostatic emmissions. For example, a modern VFD driving a typical 3-phase motor may generate a varying frequency from say... 5hz through 120hz as it's intended design, but the switching action of the thyristors, the inductive and capacitive reactance of the load (the motor, wiring, snubber capacitors, inductors, etc) generates switching transients that are 3 and sometimes 4 orders-of-magnitude HIGHER. This coupled to long leads and improper grounding creates one awesome wideband HF radio transmitter. High-frequency arc-welders, and even just ordinary buzz-boxes also generate some incredible noise, which very easily gets fed backwards (through the power delivery system) into other equipment, and radiated into the ether.
For a radio receiver, this is a nightmare. No amount of input filtering will make the problem 'go away'... it may CUT DOWN the racket, but it'll take out a chunk of the good signal, too.
In cases where radio transmitting equipment is operating (especially broadcast), noise in the power system, as well as radiated EM energy, establishes enough of a presence in antenna and feedline structures to penetrate the transmitter's stages, mix with the transmitting signal, and generate some pretty awesome noise (transmit intermodulation) at the amplifier's output. If the amplifier is feeding through a bandpass filter, this out-of-band racket is basically absorbed by the filter, turned into heat. SOME of it will get through the filter, out to the antenna, and broadcast a LONG way.
In the realm of NON-radio tx/rx, this exact same racket can cause some screwy stuff in computers, remote-control systems, just about anything with microprocessors. A strong-enough signal will be interpreted as logic contrary to what exists, and an even-stronger signal will turn a chip into a fuse...
I'll say this (probably to the chagrin of many professionals), and it is true:
--There is no such thing as a 'good' ground. There's bad, and better.
--Grounding has characteristics. Like a wire conductor, the earth succombs to 'skin effect', and that effect has everything to do with resistance, inductance, and capacitance.
--AC grounding assumes 50 or 60hz AC.
--DC grounding assumes some relatively-fixed DC voltage.
--Lightning doesn't care what YOU think... there's a whole lotta DC there, and since you're parked inside a little VanDeGraaf generator, banging on a huge electromagnetic bell- you're gonna get AC at every possible frequency and amplitude, at least for a minute period of time.
--RF systems use common AC power, DC power, and considerably higher RF AC signals and power. The intention is to both transmit and receive AC signals that are typically substantially HIGHER than AC used in power systems. While they use the grounding system for AC and DC safety, fire protection, and equipment protection, they ALSO usually need to use the grounding system as a reference point (aka Counterpoise) for receiving and transmitting. The nature of this action is MUCH more demanding than the requirements of safety, fire protection, and equipment protection. An ordinary pair of grounding wires, connected per NEC code, using common techniques and bearing inspectors' approvals, can work fine in the power system, but very easily become a diode at RF frequencies.
--AC systems that generate garbage OUTSIDE of their regulated frequency shouldn't, but they do. An 'effective' grounding system (note that I didn't say 'perfect') will do a good job at quenching accidental, unavoidable garbage... and will also do a good job keeping RX/TX systems from being subjected to it.
[aside note- I've noticed that many wire tables and info now include 'skin effect' ratings. Generally, anything running at frequencies in the AC power distribution range experience very little propensity of 'skin effect', but I'm glad that they're starting to consider the effects of frequency on a conductor's capacity. Frankly, if you're delivering 60hz AC power through a wire, and skin effect is of great concern, you've got SOMETHING that isn't designed properly (there's noise on the line that shouldn't be there).]
Last, but not least- your question about counterpoise size versus radiating element.
Transmitting signals are either coupled as a balanced or unbalanced load. When using a ground as your counterpoise, you're transmitting into a radiating element AGAINST the ground, the transmitting load is UNBALANCED. In the case of balanced loads, you're transmitting against two radiating elements, neither of which is the ground.
Effective transmitting REQUIRES that your radiating element and it's counterpoise have a suitable resonant frequency, bandwidth, and impedance to match your transmitter and feedline. If ANY of those characteristics are incorrect, you'll have a mismatch, which equates to loss... heating on the feedline, antenna, or final amplifier, very high RF voltages (and low currents) appearing where they shouldn't, very high currents (and low voltages) where they shouldn't, and stuff smoking, burning, popping, etc.
In terms of a simple free-air dipole or ground-plane antenna, the counterpoise will have approximately the SAME 'rf length' (Xc/Xl predicate, and don't forget there's air adding capacitance). It is the combination of angle, surface, RF length, etc., that makes a basic 'ground plane' antenna an unbalanced transmit point that is within itself, a balanced load... it is a 'balun' by electromechanical design. The silly thing is... the antenna's counterpoise (in both balanced and unbalanced applications) is most effective at resonance... but in the world of good grounding, resonance is very undesireable- it's counterproductive... you don't want the earth-ground to oscillate, you want it to serve as an absorber.
In ANY event, a ground-referenced transmitting system will always be happy to have MORE counterpoise surface than less. Likewise, if you're running multiple bands (my system reaches from 400khz to over 10Ghz), there's never a concern about having too much ground-bonding or counterpoise area. By adding copper to the ground in long strips, all tied together, the resistance of the ground goes down, making it more effective.
Okay, did I break the forum? Everybody okay?
Dave Kamp, KW0D
Last edited by DaveKamp; 02-19-2008 at 04:23 PM.
Reason: Oops... made a typo.
Hello CQ,CQ,CQ calling any Subs
Makes me wanna break out the wire and insulators and see if I can do a long wire and hear some VLF (Submarines).
Frank S. in Tennessee - K4SDW (Extra Class)
:mad: cause the local buildiong supply sold me a bunch of #4 instead of #2 and now I hav ta pull new wire only stiffer through the wall - Really, really:mad::mad:.
I was gonna mention that when we lived in Florida we had sandy soil and we used to rig up a 3/4" copper pipe with a transition to a water hose with a ball valve. Insert the copper clad ground into the copper water pipe, stand it up where you want it and jet that baby into the ground. Slick as a whistle. When its in deep enough you pull out the copper pipe and the earth collapses around the copper ground rod. Use to drive them in a configuration recommended by Art Collins of Collins Radio fame, a configuration of three in a triangle - interconnected.
Just as a side note cause someone opened the can of antennas stuff. I did drive a stick of copper water pipe down with water until I hit ground water (27' - 30') and tied that into my splayed ground radials for a vertical antenna - made of an excellent ground image reflector. From Florida, I was big in Europe with 100 watts.
Just my 2 cents to make it interesting. Now let me get back to the RPC.
Frank S. in Tennessee
I did the water trick here also - in clay!! I'm too old to be beating on innocent copper grounds with a hammer
Adaptation... or new application...
I used the water trick to do similar... but not drive a ground-rod...
My mom had problems with a big ground-hog undermining one tree and a good-sized chunk of her garden... was killing it all...
One day I was out pushing the lawn-boy, and felt the ground echo underfoot... realized what I'd found, but the soil was HARD and dry... so I used a 6' piece of 1/2" conduit hooked to a garden hose... pushed it down 'till it broke through into that dude's cavern.
For a moment, I considered just flooding his cabin... but stopped... let it solidify again... then dug into my stash of somewhat non-legal fourth-of-july celebration munitions...
They sure sound funny when they go off 4' underground...
And a few bottle-rockets and smoke-bombs later, that dude stuck his head up out one hole long enough for me to shoot an arrow through him. Wasn't quite able to return back down the hole...