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electrofelon

electrofelon

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Cherry Valley NY, Seattle, WA
I don't like this at all:

Very sloppy. I get the point he author is trying to make, that ungrounded systems still get metal parts bonded together and to a GES, but he consistently uses the word "system" next to "grounding" and then jumps to equipment grounding. He should clarify right in the beginning that system grounding and equipment grounding are two different things. For example, here are a few quotes:

" why do we consider an ungrounded system “ungrounded” when we are required to establish and connect a grounding electrode system to that ungrounded system?"

NO! We are not connecting a GES to the "system", it is an ungrounded system!

"Regardless of whether a grounded or ungrounded system is employed, both systems will be grounded. Don’t let the term “ungrounded” fool you. As we have discussed in this article, there is nothing “ungrounded” about an ungrounded system."

NO! An ungrounded system is an ungrounded system!
 
kwired

kwired

Electron manager
Location
NE Nebraska
electrofelon said:
I don't like this at all:

Very sloppy. I get the point he author is trying to make, that ungrounded systems still get metal parts bonded together and to a GES, but he consistently uses the word "system" next to "grounding" and then jumps to equipment grounding. He should clarify right in the beginning that system grounding and equipment grounding are two different things. For example, here are a few quotes:

" why do we consider an ungrounded system “ungrounded” when we are required to establish and connect a grounding electrode system to that ungrounded system?"

NO! We are not connecting a GES to the "system", it is an ungrounded system!

"Regardless of whether a grounded or ungrounded system is employed, both systems will be grounded. Don’t let the term “ungrounded” fool you. As we have discussed in this article, there is nothing “ungrounded” about an ungrounded system."

NO! An ungrounded system is an ungrounded system!
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I agree with you. In the "ungrounded system" we have no intentional reference to ground connected to the supply, but we still bond all non current carrying parts together to avoid having any touch potential between them and install a GES to bring those bonded objects to same potential as earth.

Then when a system conductor does fault to ground the system basically temporarily becomes grounded, and that is what the ground detection indicators are all about is to tell us there is a problem. Ignore that problem and a second fault will cause problems. If on a different conductor it should open overcurrent devices, if on same conductor that is where you will get stray current flowing on what is supposed to be non current carrying parts.
 
P

paulengr

Senior Member
He is confused partly because we use the word grounding indiscriminately. Bonding would be the better word.

“Ungrounded” is also not ungrounded. It is capacitively grounded. As noted in a bolted fault scenario on the first fault it becomes corner grounded delta. On a second fault we either get just a multi grounded delta or a line-ground-line fault.

However that’s what is taught and the theory behind the purported advantage of ungrounded systems (one fault is allowed) but it’s a false narrative because we rarely get bolted fault failures. Real failures almost always start as arcing faults.

In an arcing fault the system capacitance acts like a spark gap voltage multiplier circuit and usually destroys something else (weakest insulation) somewhere else in the system, at about 600-800% of the line to line voltage. This usually kills motors which have the weakest insulation,

 
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