Excellent.........

Solid information. Excellent presentation lots of common sense, no stinking computer needed.

Maybe we can get away from driving ground rods when we consistently see this type of grounding.

I have been doing this for a few years, when AHJ let's me. Is real handy on pole bases!

Thank you For the Info:

But remember, the use of such also causes the footings to crumble as lightning turns the moisture to steam within the footer--as a later inspection of the test power line illustrated.

Good paper and written by eminent contributors electrical systems applications. This appears to be an earlier typwritten version of the same article that was presented at the IEEE Industry & General Applications Annual Meeting and included in the I & G A Transactions magazine of Jul/Aug 1970.

The "ground" is bone dry and very resistive up here. Given that a fat wire looks like an inductor at high frequency, and that lightning and surges are usually very high frequency-like events, these bonding methods seem ineffective.

When we run a motor with a VFD, we use special layered-shielded cable now. It has a fat ground wire for grounding against shorts, but it also has layers of braid, foil, and metal conduit shielding (all plane-like) to mitigate high frequency noise from the switching. The shielding is a low impedance path at the higher frequencies- each type has its favorite frequency band where its impedance is lowest, and they overlap.

The grounding methods for buildings seems to be all wire-like or inductor-like.

Pipes: look like wires/inductors Rebar: look like wires/inductors, though in a grid they may do better grounding wire: is a wire/inductor grounding rods: look like wires/inductors

Does anyone measure the impedance of the ground and grounding system with frequency and with energy?

Matt

I would like comments on the LIghtning/steam factor. Is there any knowledge on corrosion differences due to grounding/ copper addition?

You don't ever have to drive a ground rod if you connect to the Ufer ground.

I'm really confused about the subject of using rebar in concrete as the grounding electrode. I guess this is based on field experience. In the early 1970s I was part of a crew that went around the country servicing GM Dealership signs. The pole sings were very large, 245 sq.ft. & very tall, 35 - 50 feet. The bases, foundations, were concrete with large anchor bolts and large amounts of rebar. Many of the signs we serviced had circuits shorted to the cabinet which resulted in the entire structure being energized. Most branch circuits had no grounding conductor but instead relied on the metal conduit. Over time the grounding path was lost and even though the 12 to 20 yards of concrete were in the ground, this wasn't enough to open the short circuit overcurrent device. A little boy was killed when he came into contact with one of these signs in the early 1970s in Fort Meade Florida. This resulted in the "GM Grounding Program" where a ground rod was driven next to each pole sign in a misguided effort to correct the problem. The point is this: with hundreds of feet of rebar, 20 yards of concrete, 4 ' anchor bolts and the steel structure, these signs were insulated by the concrete not grounded by it.

The GM signs were "Code" in the U.S. but not the U.K. I have had to open a wall enough times ( once ) and reconnect EMT to know why the British require that there be a redundant grounding conductor in metal conduits in all occupancies and not just in hospitals like in the U.S.

On almost all commercial wiring jobs here in Ohio a redundant grounding conductor for metal conduit is a job specification. Most customers like grounded.

Oh yeah, the experience of the amateur radio community is that the anchor bolts and reinforcing rods in a tower footer need to be bonded to each other and to an adjacent ground rod so that lightning does not blow up the footer.

However, my experience with ungrounded 480 volt systems and ther telephone company experience is that there is also a lot of damage from low energy lightning or even invisible lightning such as Saint Elmo's Fire. This is mostly a trickle of direct current from cloud to ground and well as electrostatic induction. Therefore, a sign or tower does need a reasonable local ground against the flow of direct current.

Just remember that even for the high frequency components of lightning a local ground will usually have lower inductance than the equipment grounding conductor.

Mike Cole

Mike Cole

Both authors were elevated to the Institute of Electrical and Electronic Engineers’ (IEEE) Grade of Fellow. Ralph died July 2, 1987 at the age of 76 after an outstanding career generating many technical papers on diverse subjects. Gene is still active in the IEEE.

Several variations of the Ufer rebar paper were presented such as at the PCIC, Industrial Applications Group Annual Meeting, (Later to become IAS) and led to the adoption into the NEC of the use of rebar for earthing electrode.

One must recognize that concrete in intimate contact with the earth, no matter how dry the earth, will act as a semi-conductor. Ever turn over a rock in a dry area and find under the rock moisture? Concrete such as in a parking garage on the upper floors will be a semi-insulator.

Obtain and read Ufer’s original study.

When the Lee Fagan paper was first presented there were adverse comments about the use of the Ufer grounding method especially with respect to concrete foundations such as electrical transmission towers. The comments were that Ufer grounding would blow apart concrete foundations.

Research of the IEEE Standards about 30 years ago revealed that there were two separate IEEE Power Engineering standards for transmission tower construction. One standard was for the foundation while the other was for the tower construction.

The foundation standard at that time showed rebar in the base which was NOT connected to any grounding electrodes not that such a connection would be necessary. There was a drawing of the foundation which showed “J” bolts for connection of the steel structure for the transmission tower. However, there was NO connection of the “J” bolts to the rebar. This allowed a gap in the electrical circuit from the transmission tower to the “J” bolt to the rebar to the concrete to the earth. Nor was there any grounding of the tower shown on the tower standard. This oversight has been rectified.

When ever a lightning strike hit a transmission tower the current would have to arc across the gap from the “J” bolt to the rebar which would allow the lightning current to flow through the concrete into the earth. This gap produced heat and would result in cracking the foundation. This was the explanation for the cracking of concrete foundations.

I personally was responsible for construction of a large open steel structure approximately 4 or 5 stories tall that was a chemical processing facility. Ralph was a personal friend I adopted their (du Pont) Ufer method of earthing, grounding. At least one “J” bolt in each pier was either welded or wired to the rebar cage.

During startup the structure was hit by a very large lightning strike. So massive was the lightning stroke that the concussion from the strike physically moved the mechanical actuator on three (3) of the five (5) fire water deluge systems, flooding the structure. The foundation piers had not been backfilled and were inspected for any damage. NO damage to the foundation was found. Needless to say that the operators on duty had to change their clothes.

Back in the early 1980s at a green field site in Orlando FL the individual concrete piers spaced 25 feel apart were tested. This was to be a large factory for the assembly of fire trucks. Each concrete pier was isolated and not connected to any other pier. It had not rained for several weeks and the earth was dry. The person conducting the testing of the piers had not been familiar with the Ufer grounding and came away amazed at the low resistance readings of each pier.

Flat four to six inch thick substation concrete pads using the rebar to connect to the earth through the rebar - concrete link have been tested and found to usually be under 25 ohms these flat concrete pads with the rebar installed and connected to the switch gear became the grounding method. No additional ground rods were ever installed.

In the construction of my home I installed 25 feet of # 4/0 copper conductor at the bottom of the foundation to serve as my grounding electrode 30 years ago. I forget what the resistance of the concrete encased copper conductor serving as the earthing electrode, grounding method was then. But with the secondary connected to the bastardized multigrounded neutral electrical underground distribution system measured 1.945 ohms today.

If there are large amounts of copper in the ground, UFER grounds may be a problem. See IEEE paper PCIC-2007-25 by me and Whitt Trimble. While Mr. Fagan's paper is good, cathodic protection issues were not addressed.

CMP 5 needs to address this issue in the 2011 cycle.