Ground rod noise

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umagooma

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Hello everyone!
I have a question I hope you can help me with. I have been using our new Fluke ground rod tester to verify the grounds we are putting in at the water tanks in town. We have been having problems with fuses blowing in our units that send signals to the water plant to let them know the water levels in the tanks. We are using high dollar surge protection units on each signal line at the tank s and water plant, The company will not guarantee the units unless we give them an approved ohm reading. We have installed ground rods and when I went to get a value, the meter says I have noise on the ground and the ohm reading is invalid. What causes this noise and where should I begin to look?
Thanks for any info you can help me with..........Jim ;)
 
Did you try using the Amp function and clamp around the conductor to see if there is substantial current flowing in the conductors you clamped around?
You can use a standard Clamp-on tester as well for this test.

I would also call the Fluke techs to see what they may have to say. It may that you cannot test the "grounding electrode system" with the tester, but only one ground rod at a time???
 
I know with my earth/ground resistance tester, the manual says that if there is more than 10 Volts to ground, the readings will be irrelevant. I think Fluke says over 30 Volts or 3 Amps for theirs.
The hard part is trying to figure out where the voltage is coming from as it could be from multiple sources. It sounds like with all the things you have going on at that facility, it could take a while. You?ll probably end up having to use a more sophisticated earth/ground resistance tester to check readings, as you isolate certain suspect components in the facility.
Now you can see why so many electrical contractors don?t want to get involved with this aspect of the trade.
 
I think what they are saying is 25 ohms or less. The fluke manual (on page six) states "If there is more than 3 amps or 30 volts in the ground rod, the jaw icon and the word NOISE flash on the display and the tester beeps. When noise is present the clamp reading is not valid". Before I added a second ground and attached to the grid my ohm reading was 311 ohms and .887 ma. After the second ground and grid were attached, my ohm reading was .766 and my current was 1.96 amps. The water tank has just had a county antenna installed for emergency response. Maybe the transmitter and reciever are inducing this noise? Maybe I can turn off circuit breakers one by one and see if this noise goes away. I have low resistance now which is good, but finding the noise might take awhile. :mad:

Maybe I will call the Fluke tecs. and see what they have to say................................Thanks..................Jim:grin:
 
Allow me to ask some very stupid questions. OK?

You say these are water towers right?

Are these towers mounted on large steel columns bolted to large concrete anchors using steel rebar to reinforce the concrete?

Are the pipes to/from the tank large and steel running underground for thousands of feet or miles?

I think I know the answer to all the above questions. So one more stupid question:.

If it is a water tower is mounted on steel columns bolted to concrete anchors (making a heck of an Ufer ground) with metal to/from pipes running underground for thousands of feet: What makes you think 1 or 2 ground rods is going to add any kind of benefit?

I will finish with this; your meter is not capable of reading the tower ground impedance by clamping a driven rod bonded to one of the tower legs. All it is reading is the ground rod in series with the tower. So a good educated guess is your ground rod your meter is reading is 310 ohm’s in series with a 1-ohm or less tower structure.

Only way to measure the impedance is with a 3-point Fall of Potential test with thousands of feet of cable dragged across the country side to measure a structure that big with all that pipe in the ground.

Futile effort IMO if my assumptions are correct.
 
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dereckbc said:
Allow me to ask some very stupid questions. OK?

You say these are water towers right?

Are these towers mounted on large steel columns bolted to large concrete anchors using steel rebar to reinforce the concrete?

Are the pipes to/from the tank large and steel running underground for thousands of feet or miles?

I think I know the answer to all the above questions. So one more stupid question:.

If it is a water tower is mounted on steel columns bolted to concrete anchors (making a heck of an Ufer ground) with metal to/from pipes running underground for thousands of feet: What makes you think 1 or 2 ground rods is going to add any kind of benefit?

I will finish with this; your meter is not capable of reading the tower ground impedance by clamping a driven rod bonded to one of the tower legs. All it is reading is the ground rod in series with the tower. So a good educated guess is your ground rod your meter is reading is 310 ohm?s in series with a 1-ohm or less tower structure.

Only way to measure the impedance is with a 3-point Fall of Potential test with thousands of feet of cable dragged across the country side to measure a structure that big with all that pipe in the ground.

Futile effort IMO if my assumptions are correct.
Click to expand...


brilliant:grin:
 
WOW!!! Thanks Dereck:) Now I know why this forum is so popular!! What you say makes a heck of a lot of sense. You hit the nail on the head. It is exactly as you say. What confuses me, and what made me ask this question is I just finished another water tank and by adding one ground rod in series with existing ground, I lowered the reading of ohms 50%, with no noise, to acceptable levels for the surge arrestors. Thanks for the help and knowledge this board offers. I guess I will just assume I have a good ground at the second tank and call it a day........Thanks everyone for your quick replies:grin:
 
maybe you need to isolate your towers electricly from the rest of the water system..with all the bonding to the water mains and you are the starting point and maybe the voltage to have is from that..Dereck good point and well stated..
 
Ugamooma,

Hope I did not offend you, I needed to get your attention first because I knew from your question you couldn’t see the forest with all the trees in the way. :D

Anyway lets get back to the original problem of sensors burning out, and Surge Protection Devices failing. I do a lot of work in this area, just not with Water Utilities.

Can you enlighten me as of how and where the SPD’s are being used?

I suspect the devices you used are being installed in the wrong place, or connected improperly. :confused:

Tom Baker, another forum moderator I believe has some experience in Water Utilities. So I will PM him and ask him to take a look at this.
 
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DITTO what was said above, with regards to the clamp-on ground tester I think most regular readers know how I feel about this piece of equipment. EXCELLENT when utilized in the right hands in the right location.

I have reviewed countless reports taken with this meter (clamp on) and with the 3-point test and in my opinion ALL were completed improperly.
When all the clamp on readings are .7 it is indicative of a misapplied test instrument (older meters), and a 3-point test report that says they went out 100 feet for a grid that is 20'X20' and larger and they took only ONE reading. IMO the tester was not performing the test properly.
 
dereckbc said:
Ugamooma,

Hope I did not offend you, I needed to get your attention first because I knew from your question you couldn’t see the forest with all the trees in the way. :D

Anyway lets get back to the original problem of sensors burning out, and Surge Protection Devices failing. I do a lot of work in this area, just not with Water Utilities.

Can you enlighten me as of how and where the SPD’s are being used?

I suspect the devices you used are being installed in the wrong place, or connected improperly. :confused:

Tom Baker, another forum moderator I believe has some experience in Water Utilities. So I will PM him and ask him to take a look at this.
Click to expand...






Hey Dereck.........No offense taken:grin: I appreciate any and all replies as ya'll are only trying to help me out. I probably did not give enough info to begin with.The SPD's are located on each com line as it leaves the water tank and as it enters the water treatment plant. These SPD's were purchased from a company called Meter-Treater, Inc.

They are:
TLT (Telephone Line Treater) Series: The TLT Series provides secondary transient voltage surge suppression for (per UL 497A) Telco line protocols. Units provide protection against transients that exceed the nominal operating voltage of Dial-Up, DDS, Dedicated/Leased and T1 lines.

and

SLT (Signal Line Treater) Series: The SLT Series is a multistage, hybrid protector specifically designed for low voltage and low to medium frequency applications up to and including category 4 wiring. Models are available for all EIA protocols, 4 - 20mA current loop and standard signal applications from 5Vdc to 200Vdc. Connector interface choices are modular jack, DB9, 15 & 25 and 3 position terminal block.

I am trying to provide as good of a ground as I can as every time we have a bad storm the water treatment people have to go out and replace fuses.

As Sparky stated, PVC pipe is used outside of the tank locations whenever a water line is repaired but still there is a bunch of the old iron pipe in the ground. The tech. from Meter Treater came to our town and did a study and said these would work if the resistance to ground was good. I seem to be getting good ground readings but I am baffeled by this "noise issue".:mad:
I also installed Tesco 240MSA Surge protection at each meter base at each tank.:roll:
I am getting ready to de-energize the site and see if the noise will go away. Hope the county dont get too mad when there transmitters go dead for a little while!:grin: :grin:
Will let you know what I find from that.:)

******Update***** I pulled the meter and de-energized the whole site. The noise disappeared. I then took an ohm reading and my value was .515 ohms. Thats good enough for me. I will figure out whats causing the noise this afternoon. Oh!.....Dereck, I forgot to state that they only relied on the meter base surge suppresion before I installed the new units on the com lines. Now maybe this problem will stop.......................Jim
 
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First let’s shoot the horse to kill it so we don’t go around kicking a dead horse. Even if the supply pipes to the tank are PVC, fiberglass, or have dielectric couplings is irrelevant. The concrete footings used to support the tower are more than adequate for a ground electrode. OK? The only improvement you could make is digging a trench around the base, bury a ground ring, and bond each tower leg to the ring. This would not lower the impedance significantly; it would only be a life safety issue by lowering the “Step Potential Differences” in the event a fool was dumb enough to stand under the tower during a lightning storm. Otherwise it offers no technical improvement in operation. Well it can help with SPD's more info follows.

Moving onto the SPD’s. I work in the telecom industry as a Power Protection Engineer, so I am familiar with the protectors you are using. So my first question is:

What voltage are you using?

They come in many clamping voltages from 300 used on POTS line where ringing voltage is present down to 20 volts or so for data lines. You want to use as low of voltage as possible for the application. I am not an Instrumentation Guy, but I suspect your sensors are 4-20 ma types. So you want to use SPD’s designed for 4-20 ma circuits..

Location of the SPD’s should be at the transmitter itself on top of the tower, another at ground level where it leaves the tower and dips under ground, and another as soon as it enters the control building on the perimeter wall close to the floor as possible with a direct connection to the GES

Not sure how the grounding is done in the control house, but let me briefly tell you the optimum set up.

• A ground ring encircling both the tower and control building with a bonding jumper connecting the two rings below grade.
• At each corner of the control building sink a ground rod, and bond to ring.
• Bond AC services to the rings with a rod sunk at the bond point.
• Physically bring all outside services like sensors, telephone lines, AC service, etc as close together as possible with what I will call a Ground Window, say a 6’ x 6’ area as close to the floor as possible. Like bring them all in with Conduit up through the floor or even the perimeter wall.
• Install a ground bar in the Ground Window, near as possible to the floor. Or you can install a piece of ?” plywood cladded on one side in galvanized sheet metal.
• Bond above ground bar or sheet metal directly to the ground ring with as many bonding jumpers a practical. Keep the jumpers straight and direct as possible without sharp bends.
• Bond the ground bar inside the Ground Window to the AC Service EGC bar, that should be setting very close in addition to the required GEC.
• Use shielded cables for all entry cables, Break the shields when they enter and terminate to ground bar or sheet metal.
• Bond all SPD’s to ground bar or sheet metal provided in Ground Window with very short bonding jumpers. Copper braid or straps works great.

Obviously since this is existing construction, it may not be possible to do this, so feel free to ask questions for work around.

As far as the noise current goes (stray current), I suspect it has something to do with AC services being bonded to the water pipes as required by the NEC from all the customers (or even your own AC service) using the water pipe system. You are just going to have to go by the process of elimination to find the source. IMO it is not a big deal unless it is DC current which could erode (or protect) the pipes depending on polarity.

Hope that helps.

Good Luck

Dereck
 
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Dereck So Is it possible to isolate your towers from the main water line by inserting a plastic section of pipe? or would the earth be so saturated with earthing devices it would really have no effect on the noise at that point? I hope that second question makes sense..
 
Sure you can and permited by NEC as a means to stop objectionable current. With that said a dielectric coupler is the easiest method.
 
Thanks Dereck...............Have printed out your reply for referance. The noise is less than 2 amps and my ground is good. Will figure out the noise issue later.............Thanks for all your help!:smile:
 
I have a lot of experience on Water SCADA systems. The fuse blowing and ground resistance may not be related.
What type of circuit are the fuses in- leased line, direct line?
What type and size of fuses?
Is the cable shielded and is the shield bonded?
Does the circuit with the fuses, call it SCADA, does it have a line protection unit? If so is the unit bonded to the facility grounding electrode system.
Phone lines are fairly immune to noise as they balanced and the noise is introduced into each lead equally.
Have you tested the SCADA circuit with a scope?
 
tom baker said:
I have a lot of experience on Water SCADA systems. The fuse blowing and ground resistance may not be related.
What type of circuit are the fuses in- leased line, direct line?
What type and size of fuses?
Is the cable shielded and is the shield bonded?
Does the circuit with the fuses, call it SCADA, does it have a line protection unit? If so is the unit bonded to the facility grounding electrode system.
Phone lines are fairly immune to noise as they balanced and the noise is introduced into each lead equally.
Have you tested the SCADA circuit with a scope?
Click to expand...


Hello Tom and thanks for the reply.
These are direct lines with small (I think .5 amp) fuses. I know the cables are shielded and they are bonded on one end. We were told to bond only one end.I don't know if that is the correct way to bond the shields. Both ends have line protection now. All the units are bonded to the electrode system. The circuit has not been scoped. Thanks...........Jim:smile:
 
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