Grounding of natural gas metering stations

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flob

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Does the electrode conductor (1/0) stranded copper need to be buried? Please read below.

Is this a safe and acceptable method of grounding?

These stations are normally 10-12'W by 20-30' L concrete pads. We bury the 1/0 in a 10 inch trench for protection of the wire and strap down what we might have running on top of the pad.
Installed are 8? ground rods (ref NEC article 250.52 (5), article 250.53 (A,B,C) that are driven in the ground and measured with a ground tester. If a high reading is present, then another rod is attached by cadweld and repeated until we have the acceptable reading. (Preferably 5 ohms per equipment manufacture and NEC article 250.6 requires 25 ohms) After an acceptable reading is achieved, it is then repeated for each ground rod. Each rod is spaced 8? apart from each other. Then a 1/0 conductor (NEC 250.62 and NEC 250.64) is used to connect the grounding electrodes to complete a grounding electrode system.
 
First if your intent is to achieve a low resistance reading with minimal rods/electrodes separate them by 16 feet.

Second if you bury a bare electrode you have more copper in contact with the earth this can only lower resistance of the system.

Third the NEC does not require 25 ohms, it states if one rod/electrode does not achieve 25 ohms then you are required to install a second rod/electrode.

Safe and acceptable based upon what. Does this electrode system meet the required job specs?

In my opinion if you are using all available space for a grounding electrode system there is not much else you could do with driven rods (if this is what the specs call for, maybe go longer.

What type of test are you performing?
 
Flob, if you take a look at this thread, you'll see things that will make you laugh, cry, perhaps even give up the business. But most of all, you'll see that there is no requirement that your ground rods see 25 ohms by the NEC.

There could be job specs or other standards that might govern this installation that might have some requirement - but not the NEC.

flob said:
Does the electrode conductor (1/0) stranded copper need to be buried?
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To be honest, I don't understand your question.

flob said:
Is this a safe and acceptable method of grounding?
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From what I can tell, it sounds as though you're grounded to the gills. :)
 
Grounding of metering stations

Grounding of metering stations

I can't think of the model of the tester, but I think it's AMC 3 point tester.
First, we do stack rods to lower the resistance. We go around the whole pad because we run #6 grounding conductors from the pipe(cadweld), meters, xmitters, and all other electronic devices. We are in a very sandy area and that's why we chose the electrode grounding system. Does it hurt anything by going 8-10' (rod) apart from each other? The question is does the 1/0 conductor need to be buried?
 
Grounding of natural gas metering stations

I was told that that the grounding conductor (NEC 250.62 and NEC 250.64) which is the 1/0 stranded copper that connects each electrode by cadweld method had to be 30 inches deep. Since I am not using a ground ring system, does the 1/0 need to be buried 30 inches or just protected. Example: covered with 10" of dirt.
I believe the tester is an AMC 3 point.
 
flob said:
Does it hurt anything by going 8-10' (rod) apart from each other?
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Yes you are beating yourself up for little results. Minimum rod spacing should be at least 2X the rod length. It is a little technical and out of the scope of the forum but it has to do with Spheres of Influence.

Adding more rods to achieve lower impedance is the wrong way to go about it. It is much more effective to use longer deeper rods like 20, 30, and 40 feet.

For example let’s say you drive an 8-foot rod and read 100 ohms. Care to guess how many rods you are going to have to drive to theoretically get to 5 ohms? I will give you a hint. You drive the second rod and you should measure 66-ohms. Drive two more for a total of 4 and you should be at 33. Now just keep doubling the rod count to get half the impedance.

Give up yet? Try 32 rods to get to 4. Depending on conditions you could probable drive 2 20-foot rods spaced 40 feet apart and been done with it.

Secondly I would be questioning why you even need to get to 5-ohms or less, and what real purpose it serves other than some misguided manufacture recommendations. My bet is you would be very close to 5-ohms if you just used a UFER ground in the concrete pad. Then just encircle the pad with a ring ground with a bond to the UFER at each corner of the pad. Then all you have to do is stub up from the ring or rebar wherever you need a bond. Impedance would not matter with that type of setup because you just made an equipotential ground plane. It would be a lot less expensive to install and a lot more effective than any radial system you are doing now.

Now if there is some code requirement for your industry, fine, you can use the same UFER and RING concept then just drive a 20-foot rod or two to drop the impdedance down, but I doubt it would ever be needed if using a UFER. And if if were needed is a dead givaway you need to look at a chemical ground or dril rod holes and backfill with bentonite clay.
 
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Grounding of metering stations

Grounding of metering stations

My question has not been answered yet. Let me try asking another way. I have 5 ground rods in a line that's driven 8 feet down and 10' apart from each other. Now I connect a 1/0 copper stranded wire between each rod by cadweld. Does the 1/0 wire that connects between each rod need to be buried 30 inches or just protected from physical damage? This is a electrode grounding system.

I am not having trouble it getting low resistance. 1-10 ohms.
I don't mind if I overkill with grounding unless it causes me a problem I not aware of.
 
There is no NEC requirement for depth of a GEC. Attempts were made this cycle to establish a depth for the 2008, and to my knowledge they failed.

250.64 has the requirements for GECs, and there is no requirement to bury them. I don't know how good it is to bury a stranded copper 1/0 conductor, it seems to me that corrosion would be a lot greater than a solid conductor, but that's just an opinion not a fact. :)
 
georgestolz said:
I don't know how good it is to bury a stranded copper 1/0 conductor, it seems to me that corrosion would be a lot greater than a solid conductor, but that's just an opinion not a fact. :)
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George I have done this quite a bit with sub-station grids, communications towers, etc and we specify tinned stranded conductors up to 250 MCM to deal with the corrosion issue
 
dereckbc said:
George I have done this quite a bit with sub-station grids, communications towers, etc and we specify tinned stranded conductors up to 250 MCM to deal with the corrosion issue
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Well, that answers my concern about it then, thanks. :cool:
 
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