High Resistance Grounding
- Thread starter tbro723
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brian john
Senior Member
- Location
- Leesburg, VA
tbro723 said:
Continuity of service, a fault when operating a critical processes could COST a fortune.
Lower fault current on phase to ground faults.
Check Post Glover site for additional information.
http://www.postglover.com/
M. D.
Senior Member
This is also a good over view, EC&m has many good articles on this subject .
http://ecmweb.com/power_quality/electric_ground/
http://ecmweb.com/power_quality/electric_ground/
Thanks for the response
I am aware of the many advantages offered by a HRG system versus a solidly grounded one. Typically for commercial buildings you will see a solidly grounded system and I know that in the NEC it states that you should not employ an HRG system where LN loads are being served. I just can't seem to find an answer as to why a LN load is a deal breaker for an HRG system.
I am aware of the many advantages offered by a HRG system versus a solidly grounded one. Typically for commercial buildings you will see a solidly grounded system and I know that in the NEC it states that you should not employ an HRG system where LN loads are being served. I just can't seem to find an answer as to why a LN load is a deal breaker for an HRG system.
winnie
Senior Member
- Location
- Springfield, MA, USA
- Occupation
- Electric motor research
I disagree with benaround's analysis. While it is possible that L-N loads would be connected in series with the NGR and would not work correctly, it is more likely that the L-N loads would be connected back to the source. In this case, they would _function_ correctly.
The problem is that in this case, the 'N' line would be separated from ground by the NGR. During normal operation, this would make no difference. But during a ground fault, the neutral terminal would be raised to the line-neutral voltage. Since the high resistance grounding systems provides 'continuity of service', the ground fault would not be cleared, so the neutral terminal might stay at an elevated voltage for an extended duration.
It is often the case that L-N loads are designed with the expectation that the N terminal will be at ground potential. Thus there would be a safety issue with supplying L-N loads.
For what its worth, it is my opinion that if all conductors are treated as 'ungrounded' conductors, (eg. 4 pole breakers, double pole switches for L-N loads, etc.) that it _should_ be permissible to feed L-N loads on HGR systems, but this is not how the code is written.
-Jon
The problem is that in this case, the 'N' line would be separated from ground by the NGR. During normal operation, this would make no difference. But during a ground fault, the neutral terminal would be raised to the line-neutral voltage. Since the high resistance grounding systems provides 'continuity of service', the ground fault would not be cleared, so the neutral terminal might stay at an elevated voltage for an extended duration.
It is often the case that L-N loads are designed with the expectation that the N terminal will be at ground potential. Thus there would be a safety issue with supplying L-N loads.
For what its worth, it is my opinion that if all conductors are treated as 'ungrounded' conductors, (eg. 4 pole breakers, double pole switches for L-N loads, etc.) that it _should_ be permissible to feed L-N loads on HGR systems, but this is not how the code is written.
-Jon
M. D.
Senior Member
To be up front ,I know very little about this subject, I came across this http://www.criticalpowernow.com/pdfs/ClPwrAOLCase.pdf and wondered if they have line to neutral loads ,.. and if not,,then why the four pole breakers??
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