Ground Current Loops

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Anonymous Poster	Ground Current Loops 08/03/2010 6:55 PM
	Hello CR4ers: I have a UFER ground that we recently placed in our building. The building has it's own UFER ground that was placed when the building was built. Since we were bringing more loads to the building we decided to make another UFER ground since we were going to make excavations any way. This new UFER ground is located 10 ft away from the building's UFER ground. I obtained the following measurements: with the instrument set to read DC values: V=114 VDC I=4.5 mA DC With the buidling UFER having the possitive potential and therefore current 4.5 mA flowing from the building UFER to the new UFER (if you use conventional current flow, that is from positive to negative) These values with the instrument set to read AC values: V=106mV I=7.9 mA The new UFER was not connected to enything when i took the measurements. The building UFER was still in service since the building electric service was in use. The instrument i use to measure was a general purpose multimeter Fluke. Is there any reference that can give some perspective to the measurements that i took? and the other question is are my measurements relevant under the conditions and the instrument used for taking them? Thanks
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Anonymous Poster	#2 Re: Ground Current Loops 08/04/2010 3:54 AM
	UFER= concrete encased ground system, usually the reinforcing rods in concrete developed by a guy named Ufer back in WWll in Arizona try googlin it, I did
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cwarner7_11 Guru Join Date: Dec 2006 Location: Panama Posts: 4273 Good Answers: 213	#3 Re: Ground Current Loops 08/04/2010 10:45 PM
	It seems as though you have built yourself a battery. Although the potential difference over 10 feet is quite high, it is possible, depending on the composition of the concrete, the surrounding soil, etc. You are most likely experiencing galvanic corrosion in the buried components, and part of your system is likely to disappear over time. Connecting the two systems would most likely eliminate this. It does not appear to be AC leakage from the building system, because your AC readings are so low.
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baxterm Power-User Join Date: Oct 2008 Location: Thousand Islands, Ontario, Canada Posts: 187 Good Answers: 9	#4 Re: Ground Current Loops 08/04/2010 10:56 PM
	You measured 114VDC, between the two grounds? What was the current being measured from? Ground to ground? If so, then at that moment the voltage from ground to ground would have been essentially zero.
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NotUrOrdinaryJoe Guru Join Date: Apr 2008 Location: Lexington, KY Posts: 1639 Good Answers: 73	#5 Re: Ground Current Loops 08/05/2010 7:41 AM
	Just because a digital meter displays a number doesn't mean that you are taking a good measurement. This is because digital meters have high impedance inputs that are very sensitive to potential difference (i.e. electric fields). Chances are that if you repeat your measurement with an analog meter you will not be able to obtain the same numbers or anything even close to them. If you don't have an analog meter handy then a good reality check is to take a resistor in parallel with your digital leads such as a 100K ohm and measure again. If the potential is real, it will persist. If not, you will measure nothing which means that your digital meter was measuring a static charge. If there is a battery effect, you should be able to short between the two briefly and the voltage will recover fairly quickly. A good indicator that the meter is not really connected to anything substantial is to watch the numbers for changes. If the numbers seem to be jumping around a lot, try the reality check mentioned above. __________________ A great troubleshooting tip...."When you eliminate the impossible, whatever remains, however improbable, must be the truth." Sir Arthur Conan Doyle
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vsar Guru Join Date: May 2010 Location: Metro.Manila, Philippines. Posts: 1271 Good Answers: 27	#6 Re: Ground Current Loops 08/05/2010 11:18 AM
	By doing that, you just created another ground loop in the building. What you need to do is, tie the different loops together using a good and acceptable bonding technique and connect them together to a common rod buried to the ground. Difference in length of the different grounding conductors will equate to difference in resistance which will be translated into different equi-potential readings obtained. __________________ vsar
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Anonymous Poster	#7 Re: Ground Current Loops 08/09/2010 4:52 PM
	My mistake the DC measurements are in milli VDC. 114 mVDC. So i will take readings again with a 100 ohm resistor to make sure it is not just noise picked up by the fluke since it is usch a small measurement.
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baxterm Power-User Join Date: Oct 2008 Location: Thousand Islands, Ontario, Canada Posts: 187 Good Answers: 9	#8 In reply to #7 Re: Ground Current Loops 08/09/2010 5:04 PM
	Well, that is just a tad different. I'd just bond the two systems together, with something substantial, like 00 or 000 and be happy with it.
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Anonymous Poster (3); baxterm (2); cwarner7_11 (1); NotUrOrdinaryJoe (1); vsar (1)

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