I've been using a clamp-on grounding resistance metter to measure the resistance of the grounding elecrtode systems in some of my buildings. The meter tells me I have "noise" on the system and that may prevent getting a accurate resistance reading. I get this "noise' on 2 of my buildings so far. One building is typical 2 story office building and the other is a small correctional facilty. I am also reading a small amount of AC current on the electrode system.from .55 amps to 1.83 amps. Is any of this normal and what causes the "noise"?
noisey grounding electrode conductor
- Thread starter fredelect
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It is the current flowing on the grounding conductors that is the NOISE preventing you from taking the measurement. You are going to have to find the source before the meter will work. Most likely cause is a multi-grounded neutral conductor, or it can even be perfectly normal in a large building, even homes where soil resistance is low or common metal water pipes.
Means pretty much what it sounds like. At the service entrance you bond the service grounded conductor to earth via the grounding electrode conductor. Then from that point on the neutral and equipment grounding conductors are kept isolated from each other os required by code. If you bond them downstream to each other, you effectively turn the equipment grounding conductor into a neutral current carrying conductor because they are now in parallel.
Now with that said you may or may not have a problem especially in a large building. At the service transformer, the neutral is bonded to ground. From the service transformer, only the grounded circuit conductors carried to the service entrance, no ground conductors. At your service entrance you are required to bond the grounded service conduct to ground again. If you have fairly low earth impedance, load current will flow on the grounding electrode conductor.
For example if your service entrance grounded service conductor impedance is .1 Ohm's, and your grounding electrode is 10 Ohm's with 100 amps flowing on the service grounded conductor, you will have 1 amp flowing on the ground electrode conductor. No way around that.
Now with that said you may or may not have a problem especially in a large building. At the service transformer, the neutral is bonded to ground. From the service transformer, only the grounded circuit conductors carried to the service entrance, no ground conductors. At your service entrance you are required to bond the grounded service conduct to ground again. If you have fairly low earth impedance, load current will flow on the grounding electrode conductor.
For example if your service entrance grounded service conductor impedance is .1 Ohm's, and your grounding electrode is 10 Ohm's with 100 amps flowing on the service grounded conductor, you will have 1 amp flowing on the ground electrode conductor. No way around that.
hurk27
Senior Member
- Location
- Portage, Indiana NEC: 2008
current on a service grounding electrode will not be effected by 3-wire subpanels after the main service, this is because of the main bonding jumper at the service, current on an electrode is the result of parallel currents ahead of the service and or a weak primary that could be using the buildings grounding system as a return path, anytime currents are found on the grounding you should check to see what the voltage is to Earth from the electrode, by just sticking a rod into Earth about 8' from the electrode and using a high impedance meter such as a DVM, if current is low but the voltage is high 10 volts or higher, then suspect a bad primary neutral to the transformer, if current is high and voltage is low, suspect a bad secondary neutral connection, if both voltage and current is low, you have normal parallel neutral currents on the grounding and for the most part is totally normal, to take a resistance reading with a clamp on meter you can disconnect the electrode in question if the voltage test and current test proves this is a normal parallel currents, but if the test show the possibility of a lost neutral on the primary or secondary then under no circumstance disconnect any grounding until the problem has be resolved, or you could wind up having the primary voltage in your hands.
Another way to get this reading is to turn off the main to the affected building and see if the current is gone, if not its coming from another service.
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hurk27
Senior Member
- Location
- Portage, Indiana NEC: 2008
Hey Dereck good to see back on here
I concur, just getting the idea across about MGN.
THX, been ill. Very busy now and cannot post as much. as years past. Feeling better now between snake bites, urine tract infection, and prostate problems.Hey Dereck good to see back on here
hurk27
Senior Member
- Location
- Portage, Indiana NEC: 2008
Well I 'm glad your back, could of used your thoughts in some threads
Get better, and stay away from snakes they bite
I've been hit a few times, growing up in the Everglades, it's hard not to.
the only one that scared me was a copper head, as they can hit under water, and I was swimming in a canal when I was hit, but thank God there were people around who got me to Miami fast.- Status