Ground Fault Selectivity

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mshields

mshields

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Equipment Ground Fault is covered in 230.95, 215.10, 240 and 517.17. Only 517.17 has a selectivity requirement. Is it accurate to say that, good engineering practices not withstanding, there is no code requirement for Ground Fault selectivity on Services and Feeders?
 
mshields said:
Equipment Ground Fault is covered in 230.95, 215.10, 240 and 517.17. Only 517.17 has a selectivity requirement. Is it accurate to say that, good engineering practices not withstanding, there is no code requirement for Ground Fault selectivity on Services and Feeders?
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No. Anywhere selective coordination is mentioned it implies GF selectivity.

Although not explicitly required you can also infer GF selectivity would be appropriate in 685 and when applying 240.12.
 
mshields said:
Equipment Ground Fault is covered in 230.95, 215.10, 240 and 517.17. Only 517.17 has a selectivity requirement. Is it accurate to say that, good engineering practices not withstanding, there is no code requirement for Ground Fault selectivity on Services and Feeders?
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Also, ungrounded and high resistance-grounded systems do not trip on ground faults. Ground fault coordination does not apply, IMO.
 
topgone said:
Also, ungrounded and high resistance-grounded systems do not trip on ground faults. Ground fault coordination does not apply, IMO.
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HRG most certainly can trip and many do. It’s just that it’s not an immediate trip. Most systems set the load trips at 1 second or less and each layer of distribution breakers delayed by a couple seconds. Time-current curve coordination makes little sense but time coordination most certainly does.
 
paulengr said:
HRG most certainly can trip and many do. It’s just that it’s not an immediate trip. Most systems set the load trips at 1 second or less and each layer of distribution breakers delayed by a couple seconds. Time-current curve coordination makes little sense but time coordination most certainly does.
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Don’t you mean LRG?
 
Xptpcrewx said:
Don’t you mean LRG?
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No. With HRG you don’t HAVR to trip and usually the resistor is continuous duty but you can. In mining they nearly always trip because their Codes require it. Like ungrounded phase loss indicators though if you don’t trip it gets ignored. The system along with ground continuity checking is illustrated in the IEEE green book.

With LRG whether 100 A or 400 A the problem is with that wattage normally a 10 second or maybe 1 minute resistor gets installed. You must trip in a timely manner ir the resistor is destroyed.
 
paulengr said:
No. With HRG you don’t HAVR to trip and usually the resistor is continuous duty but you can. In mining they nearly always trip because their Codes require it. Like ungrounded phase loss indicators though if you don’t trip it gets ignored. The system along with ground continuity checking is illustrated in the IEEE green book.

With LRG whether 100 A or 400 A the problem is with that wattage normally a 10 second or maybe 1 minute resistor gets installed. You must trip in a timely manner ir the resistor is destroyed.
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Wondering what the advantage is of an HRG scheme if you trip out the entire SDS for a single ground fault anywhere on the system (including for a faulted device on a small branch circuit). A solidly grounded system would seem to make the most sense over an HRG system that is configured to trip because the solidly grounded system would automatically sectionalize the faulted circuit while leaving the rest of the distribution system in service and unaffected. HRGs are usually applied to maintain service continuity under ground fault conditions, so if you choose to trip on this, I would think it would be more problematic (particularly in mining applications - where production uptime is critical). Yes there’s a benefit in terms of minimum equipment damage for iron core machines on HRG systems (irrespective if you trip or not), but it seems backwards if the objective is continuity of service and uptime. Still wondering what codes require this…
 
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