ground bar / neutral bar bonded together

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LarryFine said:
Which can only be attained if there is enough continuity between the neutral of the system and the conductive surface where the fault contact is being made.

That was my point.
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Larry see Don's post.

I know the point you where making but IMO it was coming across like we needed a grounded conductor in the branch circuit under protection.

Which in a line to line circuit we do not need.

Besides, when is a GFCI every installed on ungrounded systems? :)
 
iwire said:
Larry see Don's post.
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"Okie-dokie!" ~ The Rev. Jim Ignatowski from Taxi
don_resqcapt19 said:
True, but if there is no current flow there is no hazard and no reason for the GFCI to trip. In the event that some condition such as capacitance or a partial ground would permit current flow in excess of 5mA, then the GFCI will trip even on an "ungrounded system".
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True enough. One could argue that a circuit with that much capacitive coupling is not quite an "ungrounded system".

The point is that there must be enough conductance between the supply circuit and the earth for the required trip current to be attained. If there is enough coupling to create a shock hazard, there is enough for the GFCI to function.

iwire said:
I know the point you where making but IMO it was coming across like we needed a grounded conductor in the branch circuit under protection.

Which in a line to line circuit we do not need.
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Agreed, only the supply system, and the GFCI's neutral pigtail.

iwire said:
Besides, when is a GFCI every installed on ungrounded systems? :)
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I dunno. Are there any places where GFCI protection is required that are powered by ungrounded systems?
 
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LarryFine said:
Okie-dokie!
True enough. One could argue that a circuit with that much capacitive coupling is not quite an "ungrounded system".
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Well actually it still is an ungrounded system to the NEC and causal conversation.

We don't call a typical ungrounded delta 'not quite ungrounded delta' even though they all have capacitance coupling.

But again there is no application of GFCIs on ungrounded systems.

JMO, Bob
 
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LarryFine said:
I dunno. Are there any places where GFCI protection is required that are powered by ungrounded systems?
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No I don't believe so.

Other than isolated systems in hospitals I don't believe you can supply a 15 or 20 amp 125 volt receptacle from an ungrounded system.
 
LarryFine said:
Then we'll just have to agree to agree. :D
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:cool:

Well I do agree with you.:)

If you installed a GFCI on a truly isolated system it would not operate but than as Don said at that point the GFCI would not be needed for personal protection.
 
Between 4-6 ma of current imbalance the GFI trips. If there is no current imbalance there is no shock. The GFI protects against shock by monitoring for current imbalance. The GFI works on grounded or ungrounded systems.
 
hardworkingstiff said:
The GFI works on grounded or ungrounded systems.
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It can not work on a truly isolated ungrounded system.

It can't work because if the system is isolated from ground there will be no current imbalance created for the GFCI to detect.

It certainly works fine on an ungrounded circuit supplied from a grounded system.
 
iwire said:
It can not work on a truly isolated ungrounded system.

It can't work because if the system is isolated from ground there will be no current imbalance created for the GFCI to detect.

It certainly works fine on an ungrounded circuit supplied from a grounded system.
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I agree with Bob. The system would need to be grounded. Although it would work on a completely ungrounded system if you came in contact with another circuit conductor that could provide a return path outside of the path provided by the GFCI.
 
infinity said:
I agree with Bob. The system would need to be grounded. Although it would work on a completely ungrounded system if you came in contact with another circuit conductor that could provide a return path outside of the path provided by the GFCI.
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The system needs to be grounded in order to have a shock condition under one fault. The ungrounded system would require two faults in order for the GFI to trip (since that is the only way you could have current imbalance).
 
hardworkingstiff said:
The system needs to be grounded in order to have a shock condition under one fault. The ungrounded system would require two faults in order for the GFI to trip (since that is the only way you could have current imbalance).
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On what kind of ungrounded system?

If it was a single phase ungrounded system that would be a line to line fault, no imbalance but a short circuit.

If it was a 3 phase system it would either be as above or it could be both a short circuit and an imbalance.

No such thing as (legal) ungrounded Wye that I am aware of.:)
 
hardworkingstiff said:
The system needs to be grounded in order to have a shock condition under one fault. The ungrounded system would require two faults in order for the GFI to trip (since that is the only way you could have current imbalance).
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So if circuit 1,3 have a 240 volt GFCI CB and I come in contact with circuit 3 and circuit 5 the GFCI won't detect an imbalance?
 
infinity said:
So if circuit 1,3 have a 240 volt GFCI CB and I come in contact with circuit 3 and circuit 5 the GFCI won't detect an imbalance?
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Yes, it certainly should, as there would be current flowing through the GFCI device on one circuit conductor and flowing back to the source on a conductor that does not feed through the GFCI device.

However, this would not be a ground fault; it would be a line-to-line fault. The typical use of a GFCI is to detect accidental contact with a circuit conductor while the body is at least partially grounded.

I therefore stand on my point that a GFCI needs to be on a grounded system to perform its intended function.
 
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