Current flowing to ground

[kwired]

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.)

I agree with you, and will add often the current is coming from voltage drop on the MGN and is primary neutral current.

Turn all load off (main breaker maybe) and if you still have current on the GEC it is current from outside your premises, you likely not going to be able to do anything about it unless it is at high enough level - but has to be convincing to POCO to determine they have a problem.

This is a primary reason we have all the equipotential bonding rules around swimming pools. Fairly low neutral to ground potential will show up in the pool areas and will be more of a problem for a person submerged in water to get across even pretty low potential, by bonding everything together the entire pool can be above earth potential yet user can't be across this and true earth, they only in contact with one potential just like a bird sitting on an isolated high voltage wire on poles doesn't get electrocuted.

 

[jaggedben]

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.

The code mentions 25ohms only as a *maximum* resistance allowance for a single ground rod. There is no minimum requirement, i.e. if the grounding electrode system resistance were somehow also 0.1 ohms that would be code compliant. You really don't get to determine the resistance of the grouding electrode system (which also means you don't get to say you're not talking about a metal water pipe). It is what is, and if it happens to be low enough to carry measurable current then that's what the code *requires*.

 

[don_resqcapt19]

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.

Current is current no matter how low the value is...the earth is a parallel path and there will be current flow on the service GEC...just because you consider a small amount of current to equal no current does not change Ohms law.

 

[Strathead]

Current it current no matter how low the value is...the earth is a parallel path and there will be current flow on the service GEC...just because you consider a small amount of current to equal no current does not change Ohms law.

Ok in that case there is current flowing through the air as well so I stand by my posts and concept

 

[Strathead]

The code mentions 25ohms only as a *maximum* resistance allowance for a single ground rod. There is no minimum requirement, i.e. if the grounding electrode system resistance were somehow also 0.1 ohms that would be code compliant. You really don't get to determine the resistance of the grouding electrode system (which also means you don't get to say you're not talking about a metal water pipe). It is what is, and if it happens to be low enough to carry measurable current then that's what the code *requires*.

Actually 25 ohms isn’t the maximum allowed by code. Code has no maximum.

 

[Dsg319]

Actually 25 ohms isn’t the maximum allowed by code. Code has no maximum.

It’s the maximum allowed for a single ground rod, it’s just the reverse way of saying a single ground rod must have a resistance of 25ohms or less.


This thread has proven in many ways no matter what that the service neutral will have parallel paths back to the source wether or not NEC recognizes it or not. There’s no way around it.

 

[Dsg319]

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

Extend your test meter test lead and go from service point neutral to the ground wire coming down the utility pole which should be directly connected to neutral.

 

[Strathead]

It’s the maximum allowed for a single ground rod, it’s just the reverse way of saying a single ground rod must have a resistance of 25ohms or less.


This thread has proven in many ways no matter what that the service neutral will have parallel paths back to the source wether or not NEC recognizes it or not. There’s no way around it.

No it says
Exception: If a single rod, pipe, or plate grounding electrode has a resistance to earth of 25 ohms or less, the supplemental electrode shall not be required.

It doesn’t require the electrode system to have 25 ohms or less to ground.

 

[jaggedben]

It doesn’t require the electrode system to have 25 ohms or less to ground.

Nor does it prohibit it.

 

[Strathead]

Nor does it prohibit it.

So?

 

[wwhitney]

The code mentions 25ohms only as a *maximum* resistance allowance for a single ground rod.

Actually 25 ohms isn’t the maximum allowed by code.

Strathead, jaggedben never said that 25 ohms is the maximum allowed by code. The quote above says it's the maximum allowed if your grounding electrode is a single ground rod. Which is correct--if your single ground rod is more than 25 ohms, you must install a supplemental electrode that isn't a water pipe.

Cheers, Wayne

 

[mtnelect]

I have dry sandy soil ... I water my ground rod every week, nothing growing yet ?

 

[don_resqcapt19]

It’s the maximum allowed for a single ground rod, it’s just the reverse way of saying a single ground rod must have a resistance of 25ohms or less.


This thread has proven in many ways no matter what that the service neutral will have parallel paths back to the source wether or not NEC recognizes it or not. There’s no way around it.

Another common parallel path is the cable TV shield as it is bonded at every building and is a continuous metal path.

 

[kwired]

Extend your test meter test lead and go from service point neutral to the ground wire coming down the utility pole which should be directly connected to neutral.

A voltage reading of over a volt or two here would be pretty good indication of problem being between your measured points.

Turn your service disconnect off and if you have pretty much any voltage reading doing this and it because of current going to/from your grounding electrodes but is just a path for something outside your home. Might be primary current might be secondary current, the primary and secondary grounded conductors are bonded together so you very well need access to things at top of the pole or inside POCO enclosures to decipher what is going on.

 

[kwired]

Ok in that case there is current flowing through the air as well so I stand by my posts and concept

Kind of yes, except air has such a high resistance you aren't easily measuring this current in most instances. You will get more current from capacitive effects than from current flowing through the resistance of that air.

 

[Strathead]

Kind of yes, except air has such a high resistance you aren't easily measuring this current in most instances. You will get more current from capacitive effects than from current flowing through the resistance of that air.

THAT is actually my point since the beginning. If you are measuring current flow on a GEC with standard measuring equipment as the OP was, you have a problem. Either a fault loose neutral or both.

 

[kwired]

THAT is actually my point since the beginning. If you are measuring current flow on a GEC with standard measuring equipment as the OP was, you have a problem. Either a fault loose neutral or both.

Unless there is bonded parallel paths to other services then it can simply be neutral current flowing over a parallel path. Metal water piping is one example with low enough resistance it could be carrying a significant amount of neutral current even though nothing is wrong.

 

[Speedskater]

Another common parallel path is the cable TV shield as it is bonded at every building and is a continuous metal path.

And causes endless problems when connected to a audio/video system, when done incorrectly.

 

[mtnelect]

THAT is actually my point since the beginning. If you are measuring current flow on a GEC with standard measuring equipment as the OP was, you have a problem. Either a fault loose neutral or both.

Thank you for your comments, people on this forum think this is BS.

 

[don_resqcapt19]

And causes endless problems when connected to a audio/video system, when done incorrectly.

I watched it start some fascia boards on fire at a fire scene where the service neutral was open. The TV cable was stapled to the boards and was carrying the service neutral current until the power was cut off.