encased grounding

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It is sad that there are people in a position of authority who do not belong in the trade to start with. It amazes me how there are people who will follow what they say anyway for whatever reason.... that is called enabling. It perpetuates the illness.
 
Ufer Grounds

Ufer Grounds

In an Article 250 training class last night in Salt Lake City we were told that the wording in Article 250.50 was deliberately changed from "if available" to "if present". This means that any structure which has rebar in the concrete must have the earth grounding system bonded to the rebar if it is new construction. The instructor said that if the concrete contractor failed to leave some rebar exposed for the electrician to bond to that it was now necessary for the electrician to chip out the concrete until he or she exposed enough rebar to make the bonding connection.

He also said that ground rods or ground plates were only necessary if rebar, Ufer grounds, ground rings or metal water pipes were not present.

Does anyone have an opinion on the comments about having to use the rebar, whether or not it is easily available? It bothers me that we might have to chip out newly poured foundations since old foundations are exempted to avoid the chipping.
 
Hi Reid,

Welcome to the forum. :D

Up here in the frozen north, when I inspect a footing I will insure that the rebar is used and brought out of the foundation. I agree that it could be a bad situation if the concrete encased electrode was cut off or not brought out of the foundation.

Normally here we see a #4 copper attached to the rebar and then brought up and out of the foundation. On commercial projects the engineer might spec out a larger wire to use as the concrete encased electrode.

Chris
 
Prevention

Prevention

Obviously the best approach is for someone to be sure the lead of rebar or copper pigtail is available. Maybe what we are saying is that if it isn't done and rework becomes necessary a time or two that folks will make sure it is done to begin with in the future.

I do recall that a house I had built in California nearly 30 years ago had rebar sticking out underneath the service panelboard, and the groudning bar inside the panel was bonded to the rebar, so this is not a new idea at all.
 
Gary Beckstrand

Gary Beckstrand

OK, I'll bite. What does Gary Beckstrand have to do with Sir Ryan Jackson? Is this guy operating under an alias because he is want in 10 states, or is that your nickname for him, or what?

Gary is pretty entertaining.
 
Reid,

Sorry, inside joke. :oops: Ryan Jackson is a moderator here, he also is an instructor in Salt Lake City. Some of the fliers for his classes have the instructor listed as Sir Ryan Jackson.

Gary Beckstrand is another Instructor that teaches classes in Utah. I agree that Gary is a great teacher and his funny slides and E-mails really make his classes fun and entertaining.

Hmmm... Ryan might be wanted in 10 states. :D

PS, Ryan is also a great teacher.

Chris
 
Appeals process neaded

Appeals process neaded

What is desperately needed in many states is a state level appeals process. I have been told that in Virginia a local AHJ can be decertified by the state if they make repeated rulings that are overturned by the state board. I sure wish we had such a system in place in every state so you could appeal bad decisions to a state level board that would be less prone to support "their man."
 
That seems a little extreme IMO. Dismantling a city's infrastructure because of a few individuals abusing their power (or failing to stay abreast of codes) seems a tad reckless.

I guess the threat is half the recipe, but... dang. :shock:
 
Incentives

Incentives

georgestolz said:
That seems a little extreme IMO. Dismantling a city's infrastructure because of a few individuals abusing their power (or failing to stay abreast of codes) seems a tad reckless.

I guess the threat is half the recipe, but... dang. :shock:
Click to expand...
I am reminded of the cartoon character Sargent Mike standing in front of a group of recruits and as always he is yelling. "That there is called a pit. That there is called a rope. The alligator is called an incentive." The first and second time you are overturned on a decision are a sufficient wake up call to warn you that your authority to enforce the states minimum / maximum code could be in jeopardy. The AHJ has to appear in person before the state board with his inspector so there is no way he/she would not know that the inspector has been overturned on a decision. The boards tone would undoubtedly get somewhat churlish prior to a member making a motion to show cause. I think that the knowledge that you can be held to a state wide standard for proficiency is enough to make local AHJs invest in training.
 
Digging up a CEE

Digging up a CEE

OK, so let me get this scenario straight.
The CEE in a new construction is not exposed when the electrician shows up to make connections. So he/she starts pounding away with a jack hammer hunting for the rebar. He/she is lucky and hits the end of a piece of rebar right away.
But wait! How long is this rebar? So he/she keeps going exposing the entire length of rebar to make sure it is 20 feet. 15 feet later the rebar is found to be cut. Now he/she starts hunting for rebar number two......
 
Re: Digging up a CEE

Re: Digging up a CEE

klillemo said:
OK, so let me get this scenario straight.
The CEE in a new construction is not exposed when the electrician shows up to make connections. So he/she starts pounding away with a jack hammer hunting for the rebar. He/she is lucky and hits the end of a piece of rebar right away.
But wait! How long is this rebar? So he/she keeps going exposing the entire length of rebar to make sure it is 20 feet. 15 feet later the rebar is found to be cut. Now he/she starts hunting for rebar number two......
Click to expand...

does the piece of rebar you are bonding to have to be 20' long itself? or is it the total length of all the rebar that is wired together inside the concrete.
 
I believe it is the total length of all of the rebar that are wired together. From 250.52(A)(3): "...consisting of at least 6.0 M (20 ft) of one or more bare or zinc galvanized or other electrically conductive coated steel reinforcing bars or rods....". Now, I would very much hate to see ten 2' pieces tied together, but I think that would meet the letter of the code.

Perhaps in klillemo's scenario, the electrician could expose the rebar in two locations, 20' apart, and check to see if there is electrical continuity between the two points? We haven't had the situation come up in my area yet. I'm not looking forward to the time when it does. We are trying to get the word out to the contractors (ECs and GCs), make sure the CEE connection is in place at footing pour and make sure it stays intact throught the project.
 
Worst case scenario

Worst case scenario

I don't know how careful the NEC language was about accepting a rebar grid as a unit or whether the bonding rebar itself has to be a 20 foot uncut length.

OK, suppose that the AHJ will accept that 1 foot of exposed rebar is acceptable for a CEE ground, because it is assumed to be connected with some 18 gauge steel wire tie to at least 20 feet of other rebar.

Now what if the exposed rebar is really only a two foot long corner piece tied to two pieces of rebar with 18 gauge steel wire ties. Is this an effective grounding electrode? Will your personal work standards accept it? Less importantly, would your insurance carrier accept it? Even less importantly, will the opposing counsel attorney be able to make something of it?

What if plastic film was laid down under the concrete floor and then covered with sand before pouring. How will you establish the concrete was in direct contact with the ground after the fact?

For other reasons, I am not at all fond of relying on rebar for ground connections. Sure, it may have a very low resistance to ground, but if it will only support a few amps before the wire ties fail what good is it? Will your personal work standards accept rebar in a poured wall as equally adequate to rebar in a poured floor?

What happens when lightning strikes and 30kA are trying to get to ground? The moisture in the concrete becomes the conductor and heats past the boiling point in a fraction of a second. The pressure generated by this vaporization explosively ruptures the concrete on the dirt side and cracks the concrete on the interior.

Now you have a mechanically compromised foundation if it is a wall, and a new path for water to seep into a basement. The ground electrode is compromised and has so poor a connection that it will not support a second lightning strike as intended. Since it is all buried behind wallboard or flooring no one will be the wiser.

I think it is better to rely on intentionally made electrodes other than CEE in order to know that the current carrying capability of a grounding electrode is adequate. There are currently no standards that specify how to use a CEE that will guarantee it to be as good as a 25 Ohm driven ground rod system.
 
You are making an assumption that there is some reason for grounding beyond the fact that code requires it. I am not sure that has been shown to be the case.

If you don't believe that is the case consider that there are basically no performance standards at all for most ground connections and the ones for ground rods are all but meaningless.

I don't believe for a minute that the CEE is going to take the full current a lightning strike can generate, but no other commonly used GE will either. Lightning is a very high frequency phenomenom. The impedance it sees in a GE is going to be very high regardless. A kink in the wire that does not matter at 60 Hz or DC, could look like a near open circuit to a lightning strike.
 
klillemo,

I will only respond to a few of your points, because I do not have the technical knowledge to be able to respond to the others.

Now what if the exposed rebar is really only a two foot long corner piece tied to two pieces of rebar with 18 gauge steel wire ties. Is this an effective grounding electrode? Will your personal work standards accept it? Less importantly, would your insurance carrier accept it? Even less importantly, will the opposing counsel attorney be able to make something of it?
Click to expand...

Does it help to know that the separate pieces of rebar are required to over lap one another by 15" or more depending upon the size of the rebar? To me it seems that we are not relying on the tie wire only for continuity, but by the metal to metal contact of the rebar, held solid by the concrete. If you must get out a jack hammer to find rebar, pick a long, straight section of foundation where it will be likely that short pieces of rebar were not used.

What if plastic film was laid down under the concrete floor and then covered with sand before pouring. How will you establish the concrete was in direct contact with the ground after the fact?
Click to expand...

This will vary from area to area, but here, I inspect electrical, and I inspect the footings. Unless there are special circumstances, which I will note on the footing inspection report, we will know that at the time the footing was poured there was an acceptable CEE connection present, and if one is not present when the electrician comes to do the service, it is because it was damaged or covered during the subsequent construction. If a plastic barrior or other circumstances impair the ability of the the footing rebar to be used as a CEE, this will be noted on the footing inspection report.

I think it is better to rely on intentionally made electrodes other than CEE in order to know that the current carrying capability of a grounding electrode is adequate. There are currently no standards that specify how to use a CEE that will guarantee it to be as good as a 25 Ohm driven ground rod system.
Click to expand...

I am certainly no expert on this, but my impression, from what I have heard and read, is that it will be very hard to find a CEE that is not better than a 25 Ohm driven ground rod system. BTW, the NEC does not require a ground rod system to have 25 Ohms or less resistance to ground as long as there are two rods present. I am sure there are many NEC compliant two rod systems out there with a resistance in excess of 25 Ohms. If driving one or two ground rods gives the electrician peace of mind, he may certainly do so. But it will not remove the NEC requirement to make use of the footing rebar present.
 
The necessity of grounding

The necessity of grounding

in reply to Petersonra
You are right. I was making the assumption that we would want the grounding electrode to act consistently with each successive lightning strike. I point out that whether this is true or not, because we are required to make use of the CEE, we now are required to subject our facility to potential foundation damage from lightning strikes. This requirement is something new and maybe not as completely thought out as it could have been. At a minimum we need better standards for the rebar assembly. If you thought the plumbers were mad at the electricians for bonding the water pipes just wait until we start telling the guys laying concrete they need to start stick welding or using listed components to assemble rebar.
I suppose that we could agree that the only reason an end user might care about a grounding electrode is due to lightning strikes because it certainly does not serve any of the other purposes such as eliminating touch potential, stabilizing line voltages, reducing lethal and/or "stray voltage".

in reply to eprice
I am glad to know that you work diligently to minimize Murphy's role in your sphere of influence. I hope this is a shared value for all of us.
I was pretty careful in the wording of my last excerpt. "There are currently no standards ..." That does not mean to say we could not come up with some techniques for better measuring grounding electrode performance, it is just that we:
1) are generally not required to measure our grounding electrode performance and
2) do not do a good enough job of characterizing electrode performance when we do

Note that when, on the occasion we do measure the performance of our grounding electrodes, we use a current and waveform that does not come near to duplicate the action encountered during a lightning strike.
I challenge us all to determine the difference between a 1Amp fuse and a 100Amp fuse simply by measuring the resistance with your hand held DVM. Until you use a current that exceeds the fuse rating, you are not likely to be able to consistently determine which is which. I can gold plate the ends of a 1Amp fuse and measure better "performance" with a DVM over an off the shelf 100Amp fuse. It is what is inside that matters and what is inside the concrete is uncontrolled. No matter how much gold you use to plate the connections up to the rebar you have not necessarily increased the system performance over a driven electrode.
When we use a CEE constructed with connections that are not designed to carry current, we will get widely varying performance in a real world application. Short of welding the rebar together, or using clamps listed for bonding one rebar to another, we are fooling ourselves into assuming the CEE is a reliable grounding electrode simply because it has a lower resistance to ground.
Contrast this with a driven ground rod of specified length with a listed connector and a specified wire size. This is a system that is assembled consistently to carry a reasonable current all along the way; or at least as far as the electrode itself. I would rather have consistent assembly to a reasonable performance standard over the inconsistent and untested assembly of rebar with only the possibility of higher real world performance.
Since the possibility of better electrode performance comes at the risk of compromising the mechanical soundness of the facility, this tips the scale for me. I simply think there are issues we have not fully addressed by this new requirement and eventually we will see a whole new class of failure modes because of it.
 
klillemo
The Concrete Encased Electrode was devised by a fella named Ufer during world war two to protect concrete ammunition bunkers situated in the desert from lightning. Mr Ufer's research revealed that the ordinary tie wires used to tie the steel together were sufficient to provide a very low impedance to ground of steel encased in concrete. Test done on those ammunition bunkers over several years showed that the impedance to ground did not increase over the life of the structure. I have been in reinforced concrete buildings during lightning strikes while the building was still only a structural shell. When the world turns a blinding white, the building shakes, and the thunder clap is both simultaneous and defining you can tell it was a direct strike. Over the course of several incidents I have never seen any spalling of the concrete. I realize that evidence is only anecdotal but if what you suggest is occurring I would have heard of at least one such incident in over forty years in the craft. I have repaired the vaporized wiring in lighting Stanchions that were mounted on reinforce concrete pylons that rise three feet out of the asphalt of the parking lot. In dozens of such repairs I never observed any spalling of the concrete from the lightning event that vaporized the wiring. And no there were no driven rods in those pylons or at least no grounding electrode conductor. Since there were no holes or liquefied spots in the asphalt I have to assume that the lightning discharged through the rebar in the pylon. I have built free standing photo voltaic powered radio shelters on ridge tops from Alaska to Argentina. I never saw any evidence of concrete spalling in the tower bases, guy wire anchors, or shelter slabs when I went out on service visits and I can assure you some of those sites are struck several times a month. You are not the first person to raise this as a possibility but if this was in fact happening in the real world I suspect we would be hearing about it.
 
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