Question about ground fault return paths to multiple sources

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Pharon

Senior Member
Location
MA
Okay, so assuming the current thinking on this topic is correct and accurate -- namely that current always wants to find a return path to its source -- during a ground fault condition, some of that current will find its way back via the grounding electrode system, and earth. Granted, it will be much less than the effective equipment grounding conductor path via the service neutral, but still -- it will be some.

Given that scenario, what about a neighborhood with multiple transformers in a close proximity to each other? If your neighbor's transformer is closer to your grounding electrode system path than your own, would that stray current find its way back to your neighbor's transformer instead of yours?

And above all, even in the case of a single transformer, is this grounding electrode fault path current measurable at the transformer?

Just trying to understand what's happening here at the atomic level. Any insight?
 

meternerd

Senior Member
Location
Athol, ID
Occupation
retired water & electric utility electrician, meter/relay tech
Impedance is everything. Current takes any and all paths back to the source. If the return side of the transformer is grounded (like most utility services are), then current takes all paths back to the grounded transformer terminal. Likely the grounded conductor in the service drop is much lower impedance than the earth, so most will take that path. If that conductor becomes open circuited, all paths will be involved.
 

SG-1

Senior Member
You do not seem convinced that the current flowing from your transformer is only interested in returning to your transformer.

In your example, your neighbors transformer & yours are bonded together by a grounded conductor, the POCO pots are wired L-G.

The circuit path would be: From your transformer windings > point of ground fault > through the earth (maybe the metal city water pipe system)> the neighbors GES > to his transformer enclosure > across the grounded conductor to your transformer enclosure > your transformer winding of orgin.

That current does not know the difference between normal load & a fault.

The current is just using the neighbors transformer enclosure as part of the path, not the windings.
 
nature always finds a way

nature always finds a way

I am reminded of a homeowner that kept losing appliances. Everybody scratched their heads till somebody noticed the guy 3 doors down stick welding in his garage. I don't remember the details but it amounted to controlled lightning.
 
Okay, so assuming the current thinking on this topic is correct and accurate -- namely that current always wants to find a return path to its source -- during a ground fault condition, some of that current will find its way back via the grounding electrode system, and earth. Granted, it will be much less than the effective equipment grounding conductor path via the service neutral, but still -- it will be some.
In inverse proportion to the ratio of the path impedances, yes.

Given that scenario, what about a neighborhood with multiple transformers in a close proximity to each other? If your neighbor's transformer is closer to your grounding electrode system path than your own, would that stray current find its way back to your neighbor's transformer instead of yours?
No. The two circuits are isolated from each other. The only connections should be through the GEC via earth and any un-isolated water piping. If there are currents induced in the ground ( and there are many, ) then the there will be a voltage difference between the neutrals, but that will not, in of itself, cause current to flow.

And above all, even in the case of a single transformer, is this grounding electrode fault path current measurable at the transformer?
Yes. Any, unbalanced current flowing in the non-grounded conductors has to appear on the grounded conductor else your grounded conductor's voltage will rise until the current difference is restored.

Just trying to understand what's happening here at the atomic level. Any insight?
Speaking atomically, electric current, as we think of it, is more an accounting trick.
 
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