ges system

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electricalist

electricalist

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dallas tx
i seem to be misunderstanding the big picture on what a ges is does and requires.
Often i hear that all grounding electrode conductors present must be utilized,,,,,cold water, bldg steel and others im not sure of them all.
then if you use cold water it needs to be suplemented with ground rod or other qualifying means..
then someone says they use 2 ground rods and thats it..
then if you use a ufer that qualifies then no other means is necessary...
it seems confusing ,,,if you must use them all if present how can 2 ground rods pass? If it was worded to imply using all avaliable and a ground rod ,,would that be the same?
 
electricalist said:
i seem to be misunderstanding the big picture on what a ges is does and requires.
Often i hear that all grounding electrode conductors present must be utilized,,,,,cold water, bldg steel and others im not sure of them all.
then if you use cold water it needs to be suplemented with ground rod or other qualifying means..
then someone says they use 2 ground rods and thats it..
then if you use a ufer that qualifies then no other means is necessary...
it seems confusing ,,,if you must use them all if present how can 2 ground rods pass? If it was worded to imply using all avaliable and a ground rod ,,would that be the same?
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It is not simple, but it may help to distinguish between existing ground electrodes such as a Ufer or water pipe and made electrodes such as driven grounds or ground rings.
If you have a Ufer, you do not need to make any additional. But you must still bond in any additional existing grounds.
If you have a water pipe but no Ufer, you may have to add at least one made ground in addition to any other existing grounds.
If you choose to use a rod as your made ground, you may need to use two instead.
 
I suggest you go read art 250 part III from start to end, it is not terribly wrong (edit: I meant long here), but there is a lot in there, maybe seeing something will trigger something in your mind and either give you a better understanding or make you ask the right question for something you don't understand.

Otherwise the two main functions of the GES is to provide a earth reference for the "grounded conductor" and to provide a place to bleed transient voltages (especially from lightning) to. The importance of the GES IMO sometimes gets too much emphasis, but it is not exactly easy to determine just how important it is or isn't either. I once had an inspector put me down like I did something terribly bad because I hadn't yet connected the GES on the project, and told me how that can have terrible results should there be a lightning strike - I let him rant on but in my mind there wasn't going to be much $$$ damages should this happen, and if it were a direct lightning strike to the facility, there was going to be damage with or without a GES.

As far as electrodes go - 250.50 starts off part III with "All grounding electrodes as described in 250.52(A)(1) through (A)(7) that are present at each building or structure served shall be bonded together to form the grounding electrode system." Note it says "electrodes that are present" you suggested that you understand it as "all grounding electrode conductors present" - not the same thing.

The first three items are items that may be present without the electrical designer/installer mandating anything to be present. If they are there you need to use them. The next four items are primarily designer/installer options, they will not be there unless part of design or specification. If none of the seven types are present you must make at least one be present and that is usually going to be one of the last four, with the driven rod being most common and most economical.

Now move on to 250.53 and it says rod pipe and plate electrodes need to be supplemented with another electrode unless they are 25 ohms or less - this is because it is typical for rod, pipe and plate electrodes to have a higher resistance then a water pipe building steel or a CEE. When a rod is the only electrode, many will just drive the second rod automatically because they don't have the means to determine if the first rod is 25 ohms or less and driving the second rod is less costly then testing the first rod anyway.

The water pipe electrode needs supplemented not because it is a poor electrode, but because metal water pipes are often replaced with non metallic pipes - and if that were the only electrode before the change - you are left with no electrode at all.

So in general it boils down to if there is a water pipe, (qualifying) building steel, or a CEE present you must all of them that are present. No supplemental electrodes required other then a supplement if water pipe is the only electrode present. A CEE or building steel does supplement a water pipe if it is also present. All other electrodes are generally optional, but at least one of those option must be included if there is no water pipe, building steel or CEE.
 
Im on my way to meet my supervisor and connect a ufer to an existing service where we added a 200 amp disc. Ive read it a few times but i still keep reading it when i stop at a light.
 
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electricalist said:
24925baed587a57ac08e887f9d0f9286.jpg
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Assuming this is the job in question - what was existing for the GES? There are several possibilities of how you could connect that added service disconnect to the GES.

As far as a CEE goes, you never need larger than 4AWG copper as sole connection to the CEE. If a CEE was added that wasn't there before - it becomes a grounding electrode for the entire service not just the one disconnect that was added. Same goes for a CEE that was already there - you shouldn't need to run a separate GEC to the CEE, just tap on to the existing run to the CEE.

With multiple disconnects there are multiple ways to do the GES but one of the simpler ways is to run a common GEC sized for the largest service entrance conductor and make taps from the other service disconnects to that common GEC. If what is existing did not do that you need to use some creativity sometimes to find the best solution.
 
250.4 (A) Grounded Systems.
(1) Electrical System Grounding. Electrical systems that
are grounded shall be connected to earth in a manner that
will limit the voltage imposed by lightning, line surges, or
unintentional contact with higher-voltage lines and that will
stabilize the voltage to earth during normal operation.
Click to expand...

the code actually tells you why electrical systems are grounded.
 
The ufer was added with the new section of bldg.
The existing disconnects had 1 to ground rod for each. From each disc to bldg steel. From bldg steel to cold water.
Within the wireway there is no connection between the disconnects to the ges except by mechanical connection. Connector to raceway etc
 
electricalist said:
The ufer was added with the new section of bldg.
The existing disconnects had 1 to ground rod for each. From each disc to bldg steel. From bldg steel to cold water.
Within the wireway there is no connection between the disconnects to the ges except by mechanical connection. Connector to raceway etc
Click to expand...
If installing from scratch I would have ran a GEC to the gutter to either the water or building steel whichever is closer, and either made separate run to other (water or steel) or use a bonding jumper between the two. CEE can also be separate run or bonding jumper - whichever is easiest or least cost and only needs to be a maximum of 4AWG if it is sole connection to the CEE. Ground rod is not even needed if you have more then just a water pipe for other elecrodes.
 
My read on the '11 Code (your profile indicates '11) is that a change in 250.68(C) would allow you to connect your new CEE to the already bonded building steel provided you meet the requirements in that section.
 
250.68C #2 ,the metal frame of a bldg shall be permitted to be used as a conductor. The existing disconnect have cold water to bldg steel . then bldg steel to each disconnect,from there to ground rod. So our ufer could go to bldg steel? Or does this need to connect at the service wireway?
 
We ran the cee to the point at bldg steel where the existing gec s meet and ask the inspector when he got here. He said it was fine with him.
Ty for the help
 
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