Objectionable current

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ishium 80439

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I'm currently working in fairly unique environment and a question has come up that has more or less formed two factions each feeling they are correct in their interpretations and I'm looking for opinions from some people who do not have a stake in the arguement.

What level, if any, of objectionable current (current at the grounding electrode) would you feel to be acceptable? I will fill in some details as warranted but I don't want to influence any responses by extraneous information too soon.

Any thoughts are appreciated.
 
The definition alone is subjective.

The current flowing on a water pipe in an area where all buildings use it as a GE may have a significantly higer current than the one in my yard that is 1/4 mile to the nearest neighbor. Neither will make a difference to the 5 hp motor, but the guy, or his lawyers, on life support may have a different viewpoint.
 
ishium 80439 said:
What level, if any, of objectionable current (current at the grounding electrode) would you feel to be acceptable? I will fill in some details as warranted but I don't want to influence any responses by extraneous information too soon.
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Residential or commercial?

At a water pipe? Depends on if this is a shared metallic water system and there is a shared transformer.

At a ground rod, "0" amps is typical.

At the neutral ground bond, "0" would be nice, but depending on the size of the system can determine the amount of leakage current. If the system is properly set up, tested and the neutral is clear of shorts to ground, the amount of current measured will be leakage current and as noted this will be site specific.

Typically in a 12 story office building (the main stay of Washington DC commercial real estate) with a 4000 amp 480/277 VAC system, we measure 2-15 amps. It should be noted this service is normally loaded about 33%.
 
I guess I need to provide more details.

I'm overseas working through many buildings that were wired under dubious circumstances at best (ie third world country/ war zone). They were ostensibly wired to either the NEC or the British Standard (depending on distribution) but needless to say they did not always have the best workers, equipment or material to work with.

We are tasked with inspecting all of the existing wiring in buildings throughout the country. When checking resistance at the ground rods (almost no metal water piping in country) there are times that we find current on the GEC.

The question that has come up is wether or not this is acceptable and if so what would be the cut off point, in terms of amps, where you would no longer be comfortable considering this system safe.

Still subjective I know, but we are being asked to make a call on this and as my previous post alluded to there are two fairly well entrenched camps on this.
 
I'm going to stick my neck out here and say that the "why" there's current on the GEC is what should be looked into. Assuming something similar to a US service entrance ( X hots and a neutral) with the neutral grounded to a rod at the panel and transformer, if the transformer is located very close to the service entrance there may not be any way to eliminate the current on the GEC. The same might apply if one rod is shared among a few services (similar to an off-peak system here) or if a number of separate rods are buried close to each other where the GEC from each panel may act to balance out the neutral loads from the different panels. In those cases, the current may not be flowing to ground per se. If the current is coming from a damaged or high impedance neutral OTOH, then that should be addressed as it will be a safety issue sooner or later.
 
PetrosA said:
I'm going to stick my neck out here and say that the "why" there's current on the GEC is what should be looked into.
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I agree with this. I don't think there's some magical cut-off point in amps.

Objectionable current is objectionable because it wouldn't be there if the job were done correctly -- IMO.

However, even a properly wired building may have current at the grounding electrodes.
 
Over 1 vac on conductors with respect to the local ground may shock 5% of the people. At 15 A this would take a ground conductor resistance of more than 0.07 ohm assuming the ground is at zero volts.

Searching on
low voltage electrocution
will give you many numbers and variables [wet hands, contact area, DC or 60 Hz, men, women, children] but they can all be reduced to a probability X that Y percent of the people will be shocked or be harmed or could die.

C. Dalziel did the original work on this so GFIs could be designed.
 
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The main question is.
Is the utility distributed similar to the US. By that I mean is the ground (conductor) used as a current carrying conductor that serves to carry the imbalance of the phase conductors.
And at the service entrance a GE & GEC separate the ground and create a neutral.
If this is the system that is used it would not be surprising to see current of the GEC as the utility ground (conductor) is in parallel with the earth itself. The GE then provides another parallel path for the utility ground.
Add to that the level of moisture in the soil/sand that can change the impedance of the ground paths.
Better grounding at the utility transformers my be needed to reduce this current on the GEC.
A simple test is to turn off the main breaker and test for current on the GEC. If the current stops the cause found and corrected. If the current does not stop it is being caused by the utility ground path and doesn't present a safety issue.

BILLY
 
Is the inspection to resolve issues or is the inspection a feel good thing from the military, that is going to try to work with some number some on picked out of the air?

If the inspection is to resolve the issue then you need to do more than a visual inspection, though on your visual inspections you can ascertain if there are visible neutral to ground connections. Additionally you can take zero sequence measurements, and neutral to ground voltage readings (with loads on). Then arrange an outage megger neutral to ground, with the neutral to ground disconnect link removed. if your testing shows shorts then lift the feeders neutrals one at a time until you find the shorted feeder then work the same at the distribution panels.

Then you can determine what is "objectionable and what you have to live with.
 
If the installation that is wired to British Standards as a TN-C-S installation (as most are) works about the same way as an NEC installation. There is a ground / neutral bond at the service entrance, which is where the ground rods connect to.

There should be very little current on the ground rod(s) as the current should be flowing on the neutral. However, electricity takes all parallel paths, so you expect to have a small percentage of the neutral current through the ground rod(s).
 
Sorry for the delay in responding and thanks for the input so far. I'll see if I can answer some of these issues.

The inspections we are doing consist of opening pretty much everything and reporting what we find. We are not looking for a 100% compliant inspection as this would be next to impossible given the circumstances. We are essentially living inside of a debate I have seen on this site many times- the difference between code compliant and safe. Through various machinations and AHJ letters etc we have come up with what are being considered "LHS" (life, health, safety issues) which need to be remedied (or at least mitigated) immediately. We also note other code violations that are given lower priority for repair (and most likely will never be addressed).

Though we have guidance on many of these issues, there are still some gray areas open to interpretation and that is where my question comes in. If X number of amps is acceptable than it gets the lower classification and may not be looked into for some time. If it gets the higher classification it needs to be at least addressed (if not necessarily solved) immediately.

Some systems are NEC, some TN-S, some TN-C-S, some generator powered, some "utility" powered. Some of the stuff has been wired well, some is scary and there is a whole lot in between.

My feeling is that the primary cause of the current we are finding is the result of the neut and ground being bonded and rebonded and rebonded along the way. Where we are gen fed I'd say that N-G jumper in the gen combined with N-G jumper in the panel is the most likely culprit.

All things considered, if I see 1A or 1.5A I'm not overly concerned. What troubles me is that we are getting opinions from higher up the food chain that readings up to 8A is acceptable before we consider this a problem that needs to be addressed right away.

That in a nutshell is the story. Thoughts?
 
OK lets cut the crap.
Somebody in Halliburton should be on trial for negligent homicide.
We have here in the US a well tested thing called the NEC.
A very simple requirement that all wiring in the sand pile be performed per the NEC and inspected by --- Oh, who would that be, sorry.

BILLY
 
Pton- I disagree. In a well designed system there shouldn't be anything flowing back on the GEC. Your comment about an equipotential plane I think misses the larger point which is where is that current coming from? It seems to me that the most likely causes for this current are multiple paths to ground and if someone servicing this system disconnects a ground splice that has 8 amps flowing across it it would be unpleasant.

However I may be missing something in my analysis which is why I came to you fine people for your thoughts.

Billy, I'm not sure what axe you are trying to grind. Halliburton has zero to do with any of the wiring in this country but I guess it is a good knee jerk reaction when looking to condemn something. In case you missed the point of my post, it is looking for answers to ensure existing installations are safe. If you care to argue this point further I would be happy to start another thread, but for now I'm looking for some input to help us better do our jobs and correct whatever mistakes may have preceded us.
 
Let's look at this, and assume a perfectly proper installation - using USA methods and distribution network.

You have the PoCo transformer, with a grounded winding.
You have a service drop, with the neutral bonded to the grounding electrode.
Your service is drawing 30 amps, all on one 'leg'.

How does that 30 amps get back to the transformer? Since electricity takes ALL paths, some of the power will return using the ground rod > mother earth > ground rod path. How much depends entirely on the relative difference in resistance between the ground and the wire used for the neutral return to the transformer. (Ohm's Law)

How much is objectionable? Well, if the 'acorn' at the rod is glowing, you probably have too much :D

Seriously, though .... such overheated connections have happened in the past simply because a squirrel had chewed through the PoCo neutral. Current flowing through the GEC isn't so much a code violation as an indication that there might be something else wrong somewhere. Or, you just might have an exceptionally conductive soil.
 
Also, I'd like to add that I don't see how "multiple neutral to ground" connections is relevant. Though not a good thing I'm having a hard time seeing how it would affect current at a ground rod.
 
ike5547 said:
Also, I'd like to add that I don't see how "multiple neutral to ground" connections is relevant. Though not a good thing I'm having a hard time seeing how it would affect current at a ground rod.
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Working various scenarios through my mind I can see how certain combinations might have a slight influence on the current to the earth. But it's the integrity of the neutral that's most important -- IMO.
 
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