Current flowing to ground

[B&V Construction]

The panel in the linked image is located in Oregon and was installed and inspected in 2012. The homeowner has been experiencing nusiance trips on one breaker which prompted an investigation.
Panel
House has a meter socket and this is the only load center. At first glance inside the panel everything looks OK, though it would perhaps benefit from a little tidying. As expected the neutral and ground are bonded using the bonding screw and the earth ground (Ufer in this case) is typical for this type of foundation. I am a bit puzzled by the multiple paths to ground though. This is 200A service and I would have expected to see a single 4AWG copper GEC. Instead there are three 6AWG conductors. This is of course incidental to the nusiance trips, but my curiousity was piqued.

And... there's current flowing on all three. At the time of my measurement the load was about 10A on one bus bar and 5A on the other, resulting in 5A returning to the service neutral. Measured with a Fluke ammeter the current on the "left GEC" was about 0.3A and on the "right GEC" about 0.1A, as well as 0.1A on the "main" GEC. Now I'm aware that there's always going to be a difference in potential between the service neutral and the earth ground. It's also unsurprising that if there's current on any of the three then there will be current on all three of them as they're parallel paths from one electrode to another. I did not, however, expect to see this much current passing to ground.

Are the "left" and "right" GECs redundant (and if so, why would the original electrician have installed them)? Are there any issues with this grounding arrangement? Is there a threshold for current bleed to a GEC before it becomes a concern? Thanks!

 

[Strathead]

It is not clear from your description whether you are talking about current on the GEC when the neutral is connected or not connected. There actually shouldn't be any difference in potential between the neutral and the ground at the service panel since they are supposed to be virtually the same point, bonded with the service bond jumper.

 

[ptonsparky]

Which breaker? What type of load?
Where do the other two 6s go?

 

[jaggedben]

That amount of current on the GECs does not generally concern me. Without knowing what the GECs go to it's impossible to say if they're redundant or if the current flow is a sign of a problem. Mutliple GECs to different electrodes is permitted and not that unusual.

 

[ptonsparky]

Amperages less than 1 are almost meaningless. Placement of the conductor in the jaws can account for some discrepancies.

 

[electrofelon]

Nothing sounds abnormal to me

 

[jim dungar]

Amperages less than 1 are almost meaningless. Placement of the conductor in the jaws can account for some discrepancies.

I agree. Most <$1k meters are not accurate below .1 values, even though they can display .001 values. Check your meter specs.

 

[infinity]

Sounds normal to me too. The installer may have pounded in two ground rods along with the CEE hence the three GEC's.

 

[kwired]

The nuisance trips likely have nothing to do with the grounding that was done here.

 

[Fred B]

Are you and electrician? Your Occ lists you as a remodel contractor.

There are many reasons for what appears to be multiple GEC, looping of the GEC between rods, bonding for water pipes or other other bonding. Without a knowledge of where the #4 and #6 is actually going hard to say definitively. #6 can be used as a bonding conductor.
#6 is allowed under 250.66(A) Ground not likely any issue related to nuisance tripping.

AFA the breaker tripping that too has too many reasons to contemplate without the additional information, such as which breaker, 1P or 2P, AFCI, GFCI, Is it an overload or short circuit from equipment being plugged into, AFCI nuisance tripping has several legitimate reasons as well as true nuisance. GFCI too has legitimate reasons to trip and reasons that would be considered a nuisance too.

 

[ptonsparky]

The nuisance trips likely have nothing to do with the grounding that was done here.

For all we know, the breakers are doing their job.

 

[kwired]

For all we know, the breakers are doing their job.

Is possible. Something tells me there is probably questionable tripping of at least one of those AFCI's however.

 

[ptonsparky]

For all we know it's the bottom right 20.
I don't think I've ever seen a panel with all the 15 amp breakers on one side.

 

[kwired]

For all we know it's the bottom right 20.
I don't think I've ever seen a panel with all the 15 amp breakers on one side.

Some are pretty adamant about how they arrange them all the 15's need to be together, 20's together, 2 poles all at top or maybe bottom, maybe depends if top or bottom feed panel...

I may do some of this at times, but others however they end up is fine. With a panel changeout sometimes you just have to land some of them where they reach and then fill in whatever will reach to any position.

 

[Speedskater]

Current will take are available paths on its return to its source, inversely proportional to the impedance of the paths.
This is just return current going back to the Neutral.

 

[Strathead]

Current will take are available paths on its return to its source, inversely proportional to the impedance of the paths.
This is just return current going back to the Neutral.

From where?

 

[kwired]

From where?

Whatever is not flowing on the neutral as a general rule. If one those electrodes would be a water pipe and connects to other buildings/other services there can also be current either to or from those other buildings.

 

[B&V Construction]

Thanks all - to answer a few of the questions above...

The service-side grounds don't have anything to do with the breaker. That breaker was replaced and is no longer an issue. The ground question just arose because I found this inside the panel and was unfamiliar with that approach for grounding.

I do not see any additional ground rods. All three GECs appear be terminated on the Ufer ground electrode. The soil in this part of the state is not dry and a single electrode is generally going to be << 25 ohms so I wouldn't have expected the electrician to drive supplementary rods. House is all PEX and there's no metallic pipe available to bond.

Although the earth ground and the service neutral are both valid paths to ground they will differ slightly in resistance. Sensitive equipment can detect it - ask a stereo enthusiast about ground loops. But you all are of course correct, they should not differ much in terms of impedance and so... now I have the opposite question: why do I not see much more current flowing to the GE, like roughly half of it?

 

[jaggedben]

...

Although the earth ground and the service neutral are both valid paths to ground they will differ slightly in resistance.

Much more than slightly. Ground resistance might typically be hundreds to thousands of times higher (unless a metal water pipe connects to the neighbors).

Sensitive equipment can detect it - ask a stereo enthusiast about ground loops. But you all are of course correct, they should not differ much in terms of impedance and so... now I have the opposite question: why do I not see much more current flowing to the GE, like roughly half of it?

Let's say the electrode-earth resistance is 5ohm (very generous) and the utility service drop is something like 200ft of 1awg aluminum to the transformer. The latter has a resistance of 0.05ohms according to the NEC. So 0.05/5 you'd expect roughly only one hundredth of the current to be flowing over the ground. You can play with the assumptions but you won't find anything close to half the current going through ground without a metal parallel conductor to the transformer neutral.

 

[B&V Construction]

Much more than slightly. Ground resistance might typically be hundreds to thousands of times higher (unless a metal water pipe connects to the neighbors).



Let's say the electrode-earth resistance is 5ohm (very generous) and the utility service drop is something like 200ft of 1awg aluminum to the transformer. The latter has a resistance of 0.05ohms according to the NEC. So 0.05/5 you'd expect roughly only one hundredth of the current to be flowing over the ground. You can play with the assumptions but you won't find anything close to half the current going through ground without a metal parallel conductor to the transformer neutral.

Yeah that makes sense - thanks!