We see current of .5 to 23 amps on our grounding systems at many different locations. Does the NEC or any other NFPA code or UL address this issue. What is acceptable? On the 23 amp system, we had the utilities company shut it down so that we could look for the sources. However, we still had 2 amps of current from stray voltages from Public Service. Some of this may be due to harmonics. Although, we have found neutrals that are bleeding into the grounded conductors. We did pay for a two point ground resistance test. All grounds from cold water, ground rod, building steel, and incased in concrete, all have less than 1 measured ohms.
Current on Grounding System
- Thread starter jphatch
- Start date
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peter d
Senior Member
- Location
- New England
You need to be more specific. Who is "we" and where are you taking these measurements? What type of facility? Inside? Outside?
The stray current may be coming from improper N-G bonds if you are talking about a premises wiring system.
Outside, the stray current is almost always caused by the utilities MGN system (multi grounded neutral) which is nothing more than a massive current divider.
The stray current may be coming from improper N-G bonds if you are talking about a premises wiring system.
Outside, the stray current is almost always caused by the utilities MGN system (multi grounded neutral) which is nothing more than a massive current divider.
Is this an Industrial or Commercial site(s)? You mention "grounding systems at many different locations", is this a single location Grounding System/Grid?
What voltages are utilized in the facility?
You mention specifically shutting down the 23 amp system. Is it a different system than the other 0.5 system?
Could you explain the comment regarding "neutrals bleeding onto the grounded conductors"?
Was the test you paid for a Fall-of-Potential test, and was the system tested as a system...not individual points? As you are aware I'm sure, to disconnect a point could be very dangerous with the currents you mentioned.
What voltages are utilized in the facility?
You mention specifically shutting down the 23 amp system. Is it a different system than the other 0.5 system?
Could you explain the comment regarding "neutrals bleeding onto the grounded conductors"?
Was the test you paid for a Fall-of-Potential test, and was the system tested as a system...not individual points? As you are aware I'm sure, to disconnect a point could be very dangerous with the currents you mentioned.
The currents you mention are not coming from a simple N-G bond unless the Neutral is open or has a hi-resistance.
You don't mention if any Meggar testing was down while the POCO had it down. If not, it was a missed opportunity.
Sorry, the design is unclear and there's just too many missing pieces.
You don't mention if any Meggar testing was down while the POCO had it down. If not, it was a missed opportunity.
Sorry, the design is unclear and there's just too many missing pieces.
Pierre C Belarge
Senior Member
- Location
- Westchester County, New York
jphatch said:
Are you or someone else measuring from one portion of the grounding system to another portion of the grounding system, with the result less than 1 ohm?
Or
Are you measuring from each portion of the grounding system to earth?
brian john
Senior Member
- Location
- Leesburg, VA
The number one cause of ground current is a IMPROPER NEUTRAL GROUND connectons.
- Location
- Massachusetts
stickelec said:
Don't worry about it, we have all done it. :smile:
We all are, anyone that thinks they know all there is about this trade is crazy.
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ptonsparky
Tom
- Occupation
- EC - retired
We have a customer with three large POCO owned transformers sitting on a pad just outside the bldg. 480 Y secondary with no neutral load. Two of the neutral conductors were tied to xfmr A then overhead to bldg point of attachment and in to several service disconnects. For some reason a third conductor was tied to xfmr C, brought in direct bury and then bonded to a gutter inside the building. We had 43 amps circulating on that loop from transformer A into the building through all the electrical equipment and back out to transformer C. (tried to insert graphic but failed)
43 amps is bad enough but what happens when the connection between xfmr B&C opens? We now have (as happend at one of their other sites) several hundred amps flowing through a small conductor and all the equipment in the building. I never used to concerned myself with how the POCO connected the secondary to their transformers. I do now.
You may have to look outside your building once you have corrected everything inside.
43 amps is bad enough but what happens when the connection between xfmr B&C opens? We now have (as happend at one of their other sites) several hundred amps flowing through a small conductor and all the equipment in the building. I never used to concerned myself with how the POCO connected the secondary to their transformers. I do now.
You may have to look outside your building once you have corrected everything inside.
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