Ok... I'm attempting to describe this...

200a Service at a detached garage and 200a feeder tapped from there to house with EGC run with the feeder and disconnect in thast panel. (Neutral bond at main panel only.)

House is suppimented with water, (required) and Garage is supplimented with a rod. (Required - Garage has several circuits from main dist. panel)

Ufer is in house structure and has GEC run to both garage, and panel in the house.

The Ufer is run in EMT and RMC in the same path as the feeder conduits, as well as a set of branch circuits, and CATV and phone conduits all in metalic conduits. No water connection between the two buildings.

Anyone see any problems with this?

e57...250.58 requires the electrode at the building to be used to ground equipment. But I don't see in the code anything that prohibits the interconnection of electrodes at seperate structures as you have described...

And 225.30 allows only one feeder or branch circuit to supply a seperate building.

shortcircuit

So the house panel has a direct connection via a GEC to the house ufer? And the detached garage has its own ground rod(s)?

But in addition there is a 'GEC' going from the garage panel to the ufer, going through the same conduit as the feeder to the house?

I can see only one potential problem: is the GEC bonded to the EMT or RMC at _both_ ends of every run? GECs can be subject to extremely high _unbalanced_ currents, and the inductance caused by the steel tube is enough to cause a serious impedance. The GEC needs to be bonded at _both_ ends of the tube in order to permit current to flow in the tube itself. See 250.64(E)

-Jon

I was wrong! Checked again and the other wire from the ufer goes to the water. Panel in the house has no GEC, and the ufer/water GEC only goes to the main, located at the detached garage. And, the garage does not have a rod, just a wire dangling out of the panel where it used to be...

Goes to show, when you think something is messed up, look again, it might be worse than you thought!

Is the only thing that is missing here the GEC connections to the feeder supplied panel at the house? By NEC alone is the Concrete Encased Electrode and the water line located at the house enough to ground the service neutral at the garage? How long is the GEC between the two buildings? Would anyone, besides me, see some virtue in running the GEC as bare number two in the trench between the house and garage?

Call me a fanatic but I would want to drive a stacked rod at the garage and add sections until I got under 25 ohms if the GEC did not show an impedance of 25 ohms or less when run to the electrodes at the house only. What's more I would make the GEC connection from those stacked rods at the service head if the service is supplied by an overhead drop. The idea of a lightning induced surge trying to find earth via the GEC run to the house would make me nervous.
--
Tom Horne

"This alternating current stuff is just a fad. It is much too dangerous for general use." Thomas Alva Edison

[This message has been edited by tdhorne (edited 01-03-2006).]

I would not call you a fanatic only concerned with your work.

I will ask Why?

What is the magic in 25 ohms?

The NEC does not require 25 ohms.

Here is part of a post from a Florida electrical instructor who is also spends a lot of time studying lighting protection systems. His info generally comes from here.

http://www.lightning.ece.ufl.edu/


His entire post can be seen here.

http://www.mikeholt.com/cgi-bin/codeforum/ultimatebb.cgi?ubb=get_topic;f=7;t=001 802;p=1#000003

Bob

[This message has been edited by iwire (edited 01-03-2006).]

Stacked rod? Que?

Oh by the way... A tree fell on the drop that fed the garage, ripped whole service off building, and being replaced new en toto. (With new ground)

I think he means a sectional rod. I have installed 20' sectional ground rods.

The one I did came in two 10' sections that screwed together.

NEC 250.56 seems to want 25ohms or less.

What am I missing Bob? I read 250.56 ('02 NEC) and it says 25 ohms or less?

The NEC does not require the GES to be less than 25 ohms to ground.


All this says is if you have only one electrode of rod, pipe or plate that it must either have less than 25 ohms of resistance to ground or be aided by other electrodes.

Once you have two electrodes there is no resistance requirement.

If you put in two rods and the resistance to ground is 50, 100, or 200 ohms the NEC is satisfied.

[This message has been edited by iwire (edited 01-12-2006).]

Re-read your post Bob and maybe I took your quote out of context. I should have said that if the system Grounding Electrode is a rod, pipe or plate it needs to be 25 ohms or less. If the System Electrode is Building Steel, a water pipe electrode, or anything other that a rod, plate or pipe the resistance is not stated in the NEC. I also agree- add another electrode and walk away from it.

This was a test Bob Did I pass?

You always pass.



I agree if it is one rod, if it is more than one electrode an infinite resistance to ground would be acceptable.

I did mean a sectional ground rod. I use the tapered rod couplers so that I only need to carry the less expensive copper weld rods that are not threaded. You just drive the first rod, place the rod coupler on top, insert the second rod into the rod coupler, and drive it to near flush, test and repeat until the desired resistance is reached. I use an electric jack hammer and a ground rod cup to do the driving.

In answer to Iwire's why.

The reason that I go for an actual measured resistance of twenty five ohms or less is in the hope of reducing the likelihood of surge and spike damage. I began doing that after a summer camp hired me to stop the destruction of their telephones, answering machines, fax machine, and so forth. I ordered protective devices and while waiting for them to be shipped I worked on the grounding. After getting the affected buildings grounded to less then twenty five ohms all of the equipment damage ceased and the staff declared me a hero. The camp is located on a ridge line in Virginia and gets lightning during most of the camping season. They weren't experiencing direct strokes to the buildings or wiring but they were going through telephone and electric control devices at several a week. I was not able to drive deep rods there so I installed ground rings and interconnected all of the separate building grounding electrodes using buried bare number two copper trenched to a five foot depth.

I got my sectional rod experience back when I was in the Air Force. I drove ground rods for telegraphic fire alarm signalling. The grounds had to be good enough to signal over with a 100 milliampere signal current in the event of a broken wire. Some of the alarm station rods went to forty feet in order to get a good ground return signal. There we used threaded sectional rods and the base had a nifty hydraulic drill to drive them. I haven't seen anything like it since. It actually drilled the threaded rods into the earth turning them as they were hammered. I wonder if a Jacobs chuck adapter on a large hammer drill would accomplish the same thing.
--
Tom Horne

" interconnected all of the separate building grounding electrodes "

From my experience with lightning in the Florida sand box I will say THAT is what fixed your lightning problem.
It is not as important what potential "ground" is, only that it is consistant throughout the system.
In theory ground electrodes are supposed to do that but in places with poor soil conductivity that local ground can be a lot different than the building several feet away.

Tom, I too have also used sectional rods in the Marines, but only in 3X3'sections for a total of nine. Whats worse than driving them, is pulling them back up! Move a generator, you get to move the same rod too.

Anyway, you would be hard pressed to get a rod 20' here, for that matter 2' will put you at bedrock on the hills. And often can not drive 8' unless at an angle.