Current flowing to ground

[BarryO]

From where?

The neutral would be grounded at the utility transformer. So you have two parallel paths for neutral current: A) through the neutral conductor, B) through the soil between the grounding electrode at the transformer, and the grounding electrode system at the service entrance. 'sounds like the current through the (B) path is about 10% of that through the (A) path.

 

[Strathead]

The neutral would be grounded at the utility transformer. So you have two parallel paths for neutral current: A) through the neutral conductor, B) through the soil between the grounding electrode at the transformer, and the grounding electrode system at the service entrance. 'sounds like the current through the (B) path is about 10% of that through the (A) path.

That sounds like a major problem. 100 feet of 1/0 copper has a resistance of around .0122 ohms, that would mean the ground's resistance would be .122 ohms in order for 10% of the current to flow through it.

 

[ptonsparky]

That sounds like a major problem. 100 feet of 1/0 copper has a resistance of around .0122 ohms, that would mean the ground's resistance would be .122 ohms in order for 10% of the current to flow through it.

IDK if that's a problem, .122 ohms ground resistance is dreamt of.

 

[LarryFine]

The neutral would be grounded at the utility transformer. So you have two parallel paths for neutral current: A) through the neutral conductor, B) through the soil between the grounding electrode at the transformer, and the grounding electrode system at the service entrance. 'sounds like the current through the (B) path is about 10% of that through the (A) path.

Consider this: Earth is not considered to be conductive enough to be considered a parallel pathway.

 

[Strathead]

IDK if that's a problem, .122 ohms ground resistance is dreamt of.

What I meant was the ground doesn't have a resistance in the 1/10th ohm range so the neutral resistance must be WAY up there for there to be that much current flowing through the earth back to the transformer.

 

[jaggedben]

What I meant was the ground doesn't have a resistance in the 1/10th ohm range so the neutral resistance must be WAY up there for there to be that much current flowing through the earth back to the transformer.

It's a valid point, especially since he said there was no metal water pipe. But also, see posts #5 and #7. Still a very low and potentially meaningless reading. Try to crank the load on the neutral up to 50A and see if the GECs jump to 5A or just stays around 0.5.

 

[Joe.B]

Would a bad neutral connection on the utility side change the equation? (No metal pipes as alternate path)

 

[Strathead]

It's a valid point, especially since he said there was no metal water pipe. But also, see posts #5 and #7. Still a very low and potentially meaningless reading. Try to crank the load on the neutral up to 50A and see if the GECs jump to 5A or just stays around 0.5.

None of us know what he was actually seeing on his meter, but I assume he knew what he was looking at. We are talking about a clamp on ammeter function. I know the difference between meter quirks and actual current flowing in an ammeter. ANY detectable current flowing on the ground is a bad thing. So, I don't agree that the "low" reading is meaningless. .3 amps is enough to kill a person.

 

[jaggedben]

If .3 amps is a bad thing then why do we ground services in the first place? You also obviously haven't worked anywhere where most houses are connected to the underground metal water distribution system.

The 0.3 amps doesn't necessarily represent a shock hazard. It isn't going to flow through you if you unterminate the GEC, as long as the neutral isn't open.

As far as meter quirks and 'any detectable current' I'm not sure you do know what you're taking about. I have one meter that displays 0.1 amps after it's put around anything. I don't use that one when I need precise measurements.

 

[Strathead]

If .3 amps is a bad thing then why do we ground services in the first place? You also obviously haven't worked anywhere where most houses are connected to the underground metal water distribution system.

The 0.3 amps doesn't necessarily represent a shock hazard. It isn't going to flow through you if you unterminate the GEC, as long as the neutral isn't open.

As far as meter quirks and 'any detectable current' I'm not sure you do know what you're taking about. I have one meter that displays 0.1 amps after it's put around anything. I don't use that one when I need precise measurements.

IF that on ground is connected to a metal underground water pipe and only if it is then .3 amps is explainable, but not ok. We ground partly so that .3 amps that shouldn’t be there won’t flow through us.

I do “know” what I am talking about. I assume YOU compensate for the .1 amps on your meter when you take a reading, and you can tell whether current is flowing or not. If current is flowing on a GEC IT IS ALWAYS abnormal. And an indication something is wrong somewhere.

 

[don_resqcapt19]

IF that on ground is connected to a metal underground water pipe and only if it is then .3 amps is explainable, but not ok. We ground partly so that .3 amps that shouldn’t be there won’t flow through us.

I do “know” what I am talking about. I assume YOU compensate for the .1 amps on your meter when you take a reading, and you can tell whether current is flowing or not. If current is flowing on a GEC IT IS ALWAYS abnormal. And an indication something is wrong somewhere.

How is it no ok...around me where we have metal underground water piping system, it is typical to find 20% or more of the neutral current on the water pipe.

There is no hazard, but the water pipe and the service neutral are in parallel via the other service neutral in the area. The current will divide in inverse proportion to the impedance of the paths. The only time there will be a hazard is where the service neutral is open and you cut the water pipe and get between the two ends.

In a recent storm, a tree limb broke the neutral but not the ungrounded conductors. The area has a common metal underground water pipe system and the home owner did not even know there was an issue with the service drop because all of the neutral current was on the water pipe...none of the issues that you would normally associate with an open service neutral. It was that was for 2 or 3 days until the power company repaired the service drop.

There will always be current on the GEC if that GEC is connected to a common metal water piping system and it is 100% normal. If there was no current on that GEC, that would be abnormal.

 

[jaggedben]

.... If current is flowing on a GEC IT IS ALWAYS abnormal. And an indication something is wrong somewhere.

For a service GEC, I would say nearly the opposite. It is normal, first of all. The lack of current on the GEC could actually be an indication that it isn't properly connected to an electrode, although it could just as easily be lack of load or poor conductance between electrodes and earth.

(For a separately derived system I would agree with you.)

 

[BarryO]

That sounds like a major problem. 100 feet of 1/0 copper has a resistance of around .0122 ohms, that would mean the ground's resistance would be .122 ohms in order for 10% of the current to flow through it.

Definitely worth of further investigation.

What I meant was the ground doesn't have a resistance in the 1/10th ohm range so the neutral resistance must be WAY up there for there to be that much current flowing through the earth back to the transformer.

Ground conductivity in Western Oregon is very low, but yea not that low.

Try to crank the load on the neutral up to 50A and see if the GECs jump to 5A or just stays around 0.5.

Doing that with the lineman in the bucket up by the transformer can be "illuminating", from the sparks produced. I don't know why they tend to be sloppier making up the neutral connections; probably because things sorta still work.

 

[ptonsparky]

Would a bad neutral connection on the utility side change the equation? (No metal pipes as alternate path)

As in primary neutral or secondary?
Primary side is above my paygrade.
Secondary side, the GEC current may go up but not enough to blow a fuse or trip a breaker. I=E/R for simplicity sake.

 

[Strathead]

For a service GEC, I would say nearly the opposite. It is normal, first of all. The lack of current on the GEC could actually be an indication that it isn't properly connected to an electrode, although it could just as easily be lack of load or poor conductance between electrodes and earth.

(For a separately derived system I would agree with you.)

A grounding wire carries fault current, never intended current.

 

[B&V Construction]

A grounding wire carries fault current, never intended current.

That's true of an EGC but as Ben and others have pointed out, if there's not at least some current on a GEC then it implicates the ground electrode.

What's been noted is that 10% (or frankly even 1%) is the opposite situation - it suggests that the ground electrode is connected and there's too much resistance on the service neutral.

The transformer is maybe 25 yards away at ground level. I can figure out whether there's excessive resistance on the neutral next time I'm there. Might be a while though. I appreciate all of your assistance.

Bret

 

[don_resqcapt19]

A grounding wire carries fault current, never intended current.

All grounding electrode conductors that are connected to the service equipment result in a parallel path for neutral current and will always carry some current. If the only path between the building electrode and the electrode at the utility transformer is the earth, that current will be very small, but where there is a metallic path via a common metal underground water pipe, the current on the GEC will be much higher.

 

[jaggedben]

A grounding wire carries fault current, never intended current.

You're not understanding the difference between a GEC and an EGC.

 

[Strathead]

All grounding electrode conductors that are connected to the service equipment result in a parallel path for neutral current and will always carry some current. If the only path between the building electrode and the electrode at the utility transformer is the earth, that current will be very small, but where there is a metallic path via a common metal underground water pipe, the current on the GEC will be much higher.

Unless you are talking about current in the ratio of 25 ohms to .01 ohms or about .004 amps when the neutral is carrying 100 amps, which I would consider no current. please explain to me the theory that causes this current flow. BTW I’m not talking about when there is a neighborhood metal water pipe. I understand that.

 

[kwired]

Would a bad neutral connection on the utility side change the equation? (No metal pipes as alternate path)

Yes, draw your circuit out and place a resistor in place of the bad connection. It will add series resistance to that point of the circuit.