I have a situation where the electrical service is coming into the Main Panel of a facility where the Neutral, Safety Ground, and Earth Ground are all bonded together. So far so good... However, there is a branch circuit feeding out from the main approximately 100 yards to an outbuilding. While the Neutral and Grounds are not bonded there, the power user has established a separate Earth Ground reference at the outbuilding where he has connected the Ground conductors from Surge Suppressors to the separate Earth Ground. The two Earth Grounds are not bonded together. I know that I have a potentially serious Ground Loop issue here. So, while it is obvious this is not a true single point Grounding configuration, My question is; Does this particular Earth Ground configuration violate NEC?
Multiple Earth Grounds
- Thread starter jcoghlan
- Start date
- Status
- Location
- Massachusetts
The feeder to the separate building, does it contain hots, neutral and grounding conductors back to the main panel?
Only the Hot and Neutral feed back to the Main.
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
The neutrals and grounds need to be bonded at that separate structure if it does not have an EGC in the feeder. You said hot and neutral???? One hot wire?
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
If this is truly a branch circuit then driving a ground rod will not give you a egc.
marti smith
Senior Member
Would you gentlemen please cite a code reference? Thx!
jxofaltrds
Inspector Mike®
- Location
- Mike P. Columbus Ohio
- Occupation
- ESI, PI, RBO
Would it ever give you a egc?:roll:
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
Quote what you want to know a code section for. One of mine would be 250.32
lauraj
Senior Member
- Location
- Portland, Oregon
If it is indeed just a branch circuit feeding the building, single hot and neutral, no equipment ground, you may not establish your own equipment ground at the building. If there is then a ground fault, there is no ground path back to the panel to trip the breaker. All receptacles should be ungrounded receptacles, or protected by a GFCI and marked as ungrounded.
jxofaltrds
Inspector Mike®
- Location
- Mike P. Columbus Ohio
- Occupation
- ESI, PI, RBO
You have lost me. Could you re-explain this?
Thanks to all for the responses to my question thus far.
I gathered more information since my original post. So, let me elaborate a little further. Keep in mind that while this will not be easy to explain, I will do my best to paint the picture as clearly as possible.
To recap: there are 2 bldgs. A 120/240 split phase electrical service enters bldg A where the Neutral, Safety Ground, and Earth Ground are bonded together at the MAIN. From the Main; a circuit consisting of a single Phase conductor, the Neutral, and the Safety Ground are strung from bldg A some distance away to a sub panel at bldg B.
The Neutral and Grounds ARE NOT BONDED TOGETHER at bldg B.
However, the steel in bldg B is directly connected to a different Earth Ground than the steel in bldg A. While the two different Earth Grounds at the two bldgs ARE NOT BONDED TOGETHER, the Safety Ground coming from the N/G bond at the Main at bldg A is also bonded to the Earth Ground at bldg B.
Now, here is where things get interesting.
The Earth Ground at bldg B is a custom Ground System made up of an elaborate array of deeply driven interconnected Ground rods to form a Ground Ring around the bldg. Furthermore, the soil around bldg B has been chemically treated to lower the resistance between the Earth Ground System and the surrounding soil to enhance the bldg's immunity against a lightning strike.
On the other hand, the Earth Ground at bldg A consists of a single Ground rod planted in regular soil.
The inhabitants in bldg A have electrical devices installed at bldg A that appear to be collectively leaking approximately 1/3 amp of current to bldg A's Ground.
You can measure a 70 Vrms voltage potential between the Neutral and Ground at bldg A. That voltage goes away by disconnecting certain equpment loads at bldg A. Or, you can eliminate the N/G voltage at bldg A by isolating the Earth and Safety Grounds at bldg B.
It appears to me that the the electrical distribution is finding a lower impedance path from bldg A, through the Safety Ground running from bldgs A to B, to the enhanced Earth Ground reference at bldg B - as opposed to the Earth Ground established at bldg A. So, in effect, I'm thinking that the Neutral and Safety Ground at Bldg A are better bonded to the Earth Ground Reference at bldg B.
The problem is, the voltage on the Ground measured at bldg A appears to be causing that fancy Earth Ground System at bldg B to rapidly deteriorate by erosion.
The bottom line here is that I am not dealing with a true Single Point Ground System at this facility(s).
I know that.
And, I also know that I could bond the Neutral and Grounds together at bldg B, but I would violate the 2008 NEC by doing so. (Apparently this was the action taken by the bldg's owners prior to the advent of the 2008 code changes, when their electrical inspector dinged them for that practice).
It is my thought that the ideal solution would be to install an isolation transformer at bldg B to reestablish the N/G bonds at that location. But, the costs associated with doing so are prohibitive, unless there is a code violation that would encourage that action.
That is why I originally asked about NEC code violations that would be specific to the scenario described.
However, with all of that said, I'm open to any ideas that I can implement that would provide a cost effective solution to this problem.
Thank you.
I gathered more information since my original post. So, let me elaborate a little further. Keep in mind that while this will not be easy to explain, I will do my best to paint the picture as clearly as possible.
To recap: there are 2 bldgs. A 120/240 split phase electrical service enters bldg A where the Neutral, Safety Ground, and Earth Ground are bonded together at the MAIN. From the Main; a circuit consisting of a single Phase conductor, the Neutral, and the Safety Ground are strung from bldg A some distance away to a sub panel at bldg B.
The Neutral and Grounds ARE NOT BONDED TOGETHER at bldg B.
However, the steel in bldg B is directly connected to a different Earth Ground than the steel in bldg A. While the two different Earth Grounds at the two bldgs ARE NOT BONDED TOGETHER, the Safety Ground coming from the N/G bond at the Main at bldg A is also bonded to the Earth Ground at bldg B.
Now, here is where things get interesting.
The Earth Ground at bldg B is a custom Ground System made up of an elaborate array of deeply driven interconnected Ground rods to form a Ground Ring around the bldg. Furthermore, the soil around bldg B has been chemically treated to lower the resistance between the Earth Ground System and the surrounding soil to enhance the bldg's immunity against a lightning strike.
On the other hand, the Earth Ground at bldg A consists of a single Ground rod planted in regular soil.
The inhabitants in bldg A have electrical devices installed at bldg A that appear to be collectively leaking approximately 1/3 amp of current to bldg A's Ground.
You can measure a 70 Vrms voltage potential between the Neutral and Ground at bldg A. That voltage goes away by disconnecting certain equpment loads at bldg A. Or, you can eliminate the N/G voltage at bldg A by isolating the Earth and Safety Grounds at bldg B.
It appears to me that the the electrical distribution is finding a lower impedance path from bldg A, through the Safety Ground running from bldgs A to B, to the enhanced Earth Ground reference at bldg B - as opposed to the Earth Ground established at bldg A. So, in effect, I'm thinking that the Neutral and Safety Ground at Bldg A are better bonded to the Earth Ground Reference at bldg B.
The problem is, the voltage on the Ground measured at bldg A appears to be causing that fancy Earth Ground System at bldg B to rapidly deteriorate by erosion.
The bottom line here is that I am not dealing with a true Single Point Ground System at this facility(s).
I know that.
And, I also know that I could bond the Neutral and Grounds together at bldg B, but I would violate the 2008 NEC by doing so. (Apparently this was the action taken by the bldg's owners prior to the advent of the 2008 code changes, when their electrical inspector dinged them for that practice).
It is my thought that the ideal solution would be to install an isolation transformer at bldg B to reestablish the N/G bonds at that location. But, the costs associated with doing so are prohibitive, unless there is a code violation that would encourage that action.
That is why I originally asked about NEC code violations that would be specific to the scenario described.
However, with all of that said, I'm open to any ideas that I can implement that would provide a cost effective solution to this problem.
Thank you.
Rick Christopherson
Senior Member
Something doesn't sound right here. If your ground-to-neutral bond is located in building A, then this is something I would expect in building B, not A. Are you sure that building A is the one with the N-G bond? Changes in building B's ground should not be affecting the neutral to ground voltage within the building where the N-G bond exists.
It is unfortunate that the NEC eliminated the provisions for separate buildings having separate grounding electrode systems, because this sounds like the perfect situation where is would be needed (unless there are other ground paths between the two).
I would double check your neutral to ground bond in building A to verify that it is secure or is otherwise not a high resistance bond.
hurk27
Senior Member
- Location
- Portage, Indiana NEC: 2008
Ok to start your use of the terms "safety ground", "Earth ground" are and can be confusing to many here who have learned the common terms used in the NEC such as "Equipment grounding conductor" (EGC) and "grounding electrode conductor" (GEC) and even the term "neutral" have been changed in the NEC to "grounded conductor" although many of us still use the term neutral, but in any case we should try to use the common terms if we wish everyone to understand what we are dealing with.
The above in red and other things has me wondering if the main bonding jumper was installed at the main service disconnect in building A, the 70 volts your are reading between the neutral and grounding is why I bring this up, more on this later.
As they shouldn't be, but the GEC for building B and the EGC from building A should all be landed on the same grounding bar or buss in building B, this means that the grounding electrode system and equipment grounding is required to be bonded together at building B but not the neutral.
First there is no requirement to bond grounding electrodes at different buildings together, each is a different system, but they will be inherently bonded together (or should be) through the EGC that should have been run with the supply conductors from building A to building B
The design of an electrode system for lightning protection is not a concern of the NEC as long as the NEC minimum requirements have been met
If this single electrode was tested to prove that it met the NEC minimum of 25 ohms then this would be fine, otherwise a second rod would have to be installed and the 25 ohm requirement goes away, so the old saying is drive two rods and go home.
This is the part I mention above that has me worried, like I said there should have been a main bonding jumper, which with this measurement there cant be one, second it sounds like you have equipment that is either returning neutral current through the EGC's or there are accidental neutral to ground connections in these circuits that is trying to return current through the grounding, this is against the NEC and will be required to be repaired, installing the main bonding jumper will most likely cause more current to be placed on the grounding as right now this current is only trying to flow through the Earth back to source, if these circuits are a multi-wire circuits then even more problems with voltage stabilization is most likely happening, and you might find some strange voltages at the load end of these circuits, in either case the wiring of these circuits must be checked out.
Ok this statement is in error, current takes all paths back to source (the last transformer in-line from the utility) all resistance paths will add up when in parallel to allow the amount of current to flow in proportion of the applied resistance of that path, without the main bonding jumper in place, then these mis-wired circuits that are putting a load on the grounding will try to return current through earth, the problem is the earth connection point is to high of an impedance to allow enough current to flow and will cause all kinds of voltage problems on the grounding and at the loads.
Again this is part of the problems I mention above, in two parts, missing main bonding jumper, and loads using the grounding as a return path.
Yes you would and this would not solve the problem you have in other areas at building A
By the requirements in the NEC you would still be required to bond across the transformer and still have the voltage problems in building A don't look for band aids to fix a real problem.
Sounds like you might have a few code violations, but nothing that cant be fixed with the proper knowledge.
- Location
- Illinois
- Occupation
- retired electrician
There never really was a provision that permitted a separtate grounding electrode system at a second building. In previous codes you were permitted to re-ground the neutral and that tied the grounding system at the first building to the second building. The only real difference is that the size of the conductor that ties the two grounding systems together is smaller and its color is green under the current code.
hurk27
Senior Member
- Location
- Portage, Indiana NEC: 2008
I have always took 250.50 to mean that at each building you must connect the electrodes together to form an electrode system for each building? I see the wording was changed in 2005 that seems to change this.
billsnuff
Senior Member
- Location
- East of 480sparky
Sound like article 406.3d3
Rick Christopherson
Senior Member
By this statement, you have wiped out the very nature of a separately derived system. Does this mean we can strike those words from the NEC?
Rick Christopherson
Senior Member
It doesn't matter what color a wire is, if you connect it to the same current carrying conductor at two locations, it becomes a current carrying conductor (of the wrong color, no less).
hurk27
Senior Member
- Location
- Portage, Indiana NEC: 2008
I doesn't?
The first part of Don's quote is talking about previous code allowing the neutral to be used as the grounding conductor, no differant then at a service.
The second part of Dons post is talking about the 2008 removal of this allowance and the requiring of a seperate EGC ran to other buildings, so this EGC would not be current carrying like the neutral would in Dons first part of his post, and he pointed out this EGC would most likly be smaller then a neutral that was allowed pre-2008.
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
By this statement, you have wiped out the very nature of a separately derived system. Does this mean we can strike those words from the NEC?
If indeed hurk is right and there is no main bonding jumper installed at the service there would likely be similar voltage issues even if the second building was supplied through a separately derived system. The EGC for the supply would still be required to be bonded to the secondary grounded conductor and this is where the stray voltage problem is originating.
If the service does not have properly installed main bonding jumper I would take some caution at just putting one in - there could be a ground fault on a phase conductor and installing the bonding jumper could really be enlightening. Apply a load between the neutral and ground and check what happens to voltage when doing so to get an idea of what is happening.
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