Current on GEC and Bonded EMT

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Thanks so much for all your replies, its a real treasure of info.


GoldDigger said:
2. The neutral in parallel (following a different conduit path!) could easily cause the readings you saw with the heat gun. Probably no relation at all to the other EGC/GES related currents you are looking at though.
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In regards to those other readings at the incoming water line. I immedietly wrote that off as being normal since its a city water supply in parallel to the tx.... I just want to confirm that is safe to dismiss that as normal.

Testing the 3/4" copper as it enter the foundation a few inches from the actual electrode which yielded no reading....

With power on to the building under no load it was showing very low about .30 of an amp. With power off to the building that figure didn't change. What I forgot to mention with the main on to the building, when a large load was applied (in this case the heatgun again) the current on the water pipe leaped up to around 1 to 1.5 amps. It did not matter which circuit the load was plugged into.

These readings were observed immediately where the pipe enters the foundation. Checking the actual GEC yielded no results just a few inches from the actual entrance to the pipe and of course no where after the water meter was any of this observed.

Does that seem out of the ordinary?

Where I learned that some current on a GEC is normal it was the fluctuation when a load was applied that prompts me to inquire now.
 
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ardmi said:
Yes the load was applied on a different circuit as well.
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Measurements of current on the GEC itself (not on any EGC anywhere in the house) which vary with the amount or location of loads that are turned on and off is at least a suggestion that there is a high resistance neutral on the POCO side of the ground/neutral bond point.
But you have to look at the expected resistance of the run of service drop from POCO compared to the expected resistance of the GES including water pipe bond, UFER ground, etc. to decide whether it is a real problem or not.

If the current in your GEC varies with the load in the house next door, it is a very strong sign of a compromised POCO neutral.
 
GoldDigger said:
Measurements of current on the GEC itself (not on any EGC anywhere in the house) which vary with the amount or location of loads that are turned on and off is at least a suggestion that there is a high resistance neutral on the POCO side of the ground/neutral bond point.
But you have to look at the expected resistance of the run of service drop from POCO compared to the expected resistance of the GES including water pipe bond, UFER ground, etc. to decide whether it is a real problem or not.

If the current in your GEC varies with the load in the house next door, it is a very strong sign of a compromised POCO neutral.
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Thanks I hesitated on having the POCO out until I could learn more. Unless there was other signs of a corrupted poco neutral (brightening of lights etc) I assume what I describe here is not something they need to be contacted about. So its ok to consider this "normal"?

In fact that 10A load was applied on every circuit in the house and each time the water pipe went up about 1A. I figured since I did not see this current on the actual electrode or the metal raceway its in or any of the water pipes in the home that it was coming IN to the house and not OUT. Also the fact that the initial half amp or so was present on the water pipe without load and without power to the residence.
 
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ardmi said:
Thanks I hesitated on having the POCO out until I could learn more. Unless there was other signs of a corrupted poco neutral (brightening of lights etc) I assume what I describe here is not something they need to be contacted about.

In fact that 10A load was applied on every circuit in the house and each time the water pipe went up about 1A. I figured since I did not see this current on the actual electrode or the metal raceway its in or any of the water pipes in the home that it was coming IN to the house and not OUT.
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AC does not care about IN versus OUT.

If the current in the GEC to a ground electrode or any metal raceway does not change but the current in the water pipe does, that is a very good indication that some of the neutral current is finding a lower impedance path through the water pipes and out to everybody else's POCO neutral (on that same transformer secondary) than the path through your own POCO neutral.
Whether or not that indicates a problem requires knowing service conductor sizes and measured voltages to a remote ground rather than just knowing the current sharing. The fact that only 1/10th of the neutral current is going out the water pipe is an indication that it may not be bad at all or bad enough to worry about.
Is the service drop particularly long?
 
GoldDigger said:
AC does not care about IN versus OUT.

If the current in the GEC to a ground electrode or any metal raceway does not change but the current in the water pipe does, that is a very good indication that some of the neutral current is finding a lower impedance path through the water pipes and out to everybody else's POCO neutral (on that same transformer secondary) than the path through your own POCO neutral.
Whether or not that indicates a problem requires knowing service conductor sizes and measured voltages to a remote ground rather than just knowing the current sharing. The fact that only 1/10th of the neutral current is going out the water pipe is an indication that it may not be bad at all or bad enough to worry about.
Is the service drop particularly long?
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No, transformer is in front house, about 50-75 drop.

I misspoke, The gec also rose 1A under load. The raceway it is was clamped. What does that indicate. ?
 
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GoldDigger said:
1. Your clamp on ammeter readings are telling you the total net current flowing in the combination of the conduit and the conductors inside. There is absolutely no way that it can measure anything else since all of those current paths pass through the clamp.
If you want to know the net current in the conductors you will need to clamp them where you can break them out separately, as in a j-box.
.
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To note, just to understand the readings from the clamp. I also turned off 2 of the 3 circuits in that conduit and was still getting a reading. Thinking being that the conductors inside would presumably be balanced. Does that speak to anything? Like the neutral is in contact with the egc (in this case a box or conduit)?
 
ardmi said:
To note, just to understand the readings from the clamp. I also turned off 2 of the 3 circuits in that conduit and was still getting a reading. Thinking being that the conductors inside would presumably be balanced. Does that speak to anything? Like the neutral is in contact with the egc (in this case a box or conduit)?
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Apparently the currents in the wires inside the conduit are not balanced. Much more likely than that there is a totally separate source of current in the conduit metal only.
Contact between the neutral and the EGC within a single run of conduit that is not connected to other pieces of conduit will not change the balance of the current in the meter clamp. But if some of the neutral current ends up following a different piece of conduit on the way back to the panel then it could cause the reading that you see.
 
GoldDigger said:
Apparently the currents in the wires inside the conduit are not balanced. Much more likely than that there is a totally separate source of current in the conduit metal only.
Contact between the neutral and the EGC within a single run of conduit that is not connected to other pieces of conduit will not change the balance of the current in the meter clamp. But if some of the neutral current ends up following a different piece of conduit on the way back to the panel then it could cause the reading that you see.
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Gold digger, please rephrase this for me. Thank you.
 
Yes it will.
Just as it is good for more than one wire.
It is difficult to shield the magnetic field completely even with ferrous conduit.

Tapatalk!
 
Apparently the currents in the wires inside the conduit are not balanced. Much more likely than that there is a totally separate source of current in the conduit metal only.
Contact between the neutral and the EGC within a single run of conduit that is not connected to other pieces of conduit will not change the balance of the current in the meter clamp. But if some of the neutral current ends up following a different piece of conduit on the way back to the panel then it could cause the reading that you see.
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To clarify... your suggesting here that what my clamp is picking up are inbalanced wires inside the conduit.... and not actual current on the conduit itself? So that rules out a neutral to egc connection.

However, conduits close the one with the circuit in question are showing current as well but very small that disappears when the other circuit is off. That suggests its easier inducing those conduits (magnetic field?) or if the current is actually on the conduit, its backfeeding it to nearby pipes?

So bottom line.... do you think my clamp is indicating flow on the counduit itself or the inbalanced conductors inside?


p.s.- I brought it up to my employer and I was told I was wrong that my amp clamp would not accurately show flow on the conduit itself???
 
Could any of what I describe (both the EGC current and the GEC current I mentioned) be caused by a subpanel that has ground and neutral bonded?

(I did disconnect the gec at the subpanel from the rod and the current readings did not change and I did not see a bonding screw on the egc bar in it so I am pretty sure they are NOT bonded... plus there is no load off that subpanel whatsoever but I thought I would mention it anyway to rule it out completely).

Another weird thing was that their was about .5 amps on the CATV ground which is connected to the raceway at the meter socket. There was no voltage present there and there is no current on the coax either. I figure that half amp on the catv was just it running in parallel with the TX at the street thinking they are bonded together there.
 
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ardmi said:
Yesterday I had to replace a jumper around a water meter in a house.

I put my clamp meter on the GEC and the water pipe prior to the meter and I was getting somewhere in the range of .50-.75 ... so less than an amp. Nothing on the other side of the meter nor on any of the water pipes.

At the meter socket outside, they had a new ground rod sunk, the old ground rod was disconnected but next to it. I was not getting any current at the new ground rod however, I was getting about 1 VAC between the old a new rod.
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Voltage between rods is normal if they are not bonded as a result of current leaking into the ground. You can prove that to yourself by just driving two rods into the ground and then measure voltage. What you will see is gradient step potential which is normal and nothing you can do about it other than bonding them together.

The current you see on the GEC is also normal IMO and a result of the GEC being in parallel with the service grounded circuit conductor (neutral conductor). The lower the earth resistance of the GES, the higher the current is going to be.
 
ardmi said:
Could any of what I describe (both the EGC current and the GEC current I mentioned) be caused by a subpanel that has ground and neutral bonded?
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Just caught this after my last reply. Absolutely will cause current on EGC and conduit as it is now in parallel with the feeder neutral conductor. It is also a code violation. The sub should have both a neutral conductor and EGC feeder isolated from each other. They cannot be bonded together again after the service disconnect point. Section 250.24(A)(5) prohibits re-bonding (grounding) of the grounded circuit conductor (aka Neutral) on the load side of the service disconnecting means.
 
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dereckbc said:
Just caught this after my last reply. Absolutely will cause current on EGC and conduit as it is now in parallel with the feeder neutral conductor. It is also a code violation. The sub should have both a neutral conductor and EGC feeder isolated from each other. They cannot be bonded together again after the service disconnect point. Section 250.24(A)(5) prohibits re-grounding of the grounded circuit conductor (aka Neutral) on the load side of the service disconnecting means.
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In order to rule that out I did the following:
Not familiar with manufacture of subpanel but I did not see a bonding screw attached at the neutral bus bar and there was no continuity between the neutral bus bar and the metal enclosure of the subpanel.

There was no current whatsoever on the subpanels gec.

I also completely disconnected the subpanels gec from the ground rod and the current readings on the conduit did not change.
 
Just to clarify, see my last post please....

There would not be continuity between the neutral bus of a sub panel and the enclosure WITHOUT the feeder or branch neutrals connected to it.

However, you would see continuity between the sub panel neutral bus and the enclosure WITH the feeder and branch neutrals connected to it.

and to confirm, if the two were bonded, completely removing the subs gec from the ground rod would isolate the sub completely (ie current remained with gec disconnected).

note the sub in question is 3 wire feeder with rigid between main panel and subpanel to a detached building with its own ground rod. No bond screw visable on neutral bus.
 
ardmi said:
Not familiar with manufacture of subpanel but I did not see a bonding screw attached at the neutral bus bar and there was no continuity between the neutral bus bar and the metal enclosure of the subpanel.
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I am going by what you asked:

Could any of what I describe (both the EGC current and the GEC current I mentioned) be caused by a subpanel that has ground and neutral bonded?
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Based on that the answer is YES.
 
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