When a non-grounding type receptacle is replaced with a grounding type why should it be labeled “no equipment ground”? Is there a safety concern that still exists? In what scenario will the grounded type receptacle not trip?
Brian, it is not about tripping, it is to protect computers and such from lighning blast. 
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Typically a GFCI device is used as the replacement which provides an added measure of safety over the ungrounded receptacle. However GFCI protection is not a replacement for grounding so the sticker warns the end user that although there is a third hole in the device that normally is used for grounding the labeled receptacle is not grounded.
Some devices state that they must be used with a grounded receptacle or must be grounded, a 3 prong replacement receptacle without any EGC connection will not be grounded.
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How does the GFCI device provide an added measure of safety?
In what scenario does the ungrounded GFCI trip? Does it trip during a lightning strike? Does it trip if the appliance plugged into it is short circuits?
The GFCI receptacle will operate the same whether or not the branch circuit connected to it has an equipment grounding conductor. It does not require a “ground” to operate. The problem with two prong receptacles is that people often use them with one of these:
These adapters allow the connection of something with a 3-wire cord that must be grounded for safety so you end up with a device or appliance that isn’t grounded but should be.
For example, let’s say your washing machine is plugged into an ungrounded two prong receptacle with one of those adapters and it internally faults to the metal enclosure. There is no connection to the EGC so the entire metal casing of the washer is energized. You’re standing there in your bare feet on the concrete basement floor and you go to lift the lid and you get blasted, and maybe even die. If the receptacle was a GFCI instead of the old two prong with an adapter it will trip. In this case the GFCI protection is there to protect the person not the machine itself.
GFCI devices are not designed to protect against short circuits.
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I may be wrong on this but it’s my understanding that with an ungrounded GFCI will still add protection when something else, like a person, becomes the path a fault current travels on… as compared to the ground wire.
For example: say a hair drier fails internally and shorts to the chassis of the drier. With grounding wires, that current is shunted to ground and GFCI trips. Without ground wires the human becomes path to ground…and the GFCI trips.
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Sorry I used the wrong term when I said short circuit. So the GFCI will trip if the appliances has this internal fault? Why then does the GFCI not trip with a tester? Isn’t the tester mimicing this internal fault?
Also why is the sticker needed? Is there a danger that still exists?
Also how do lightning strikes or power surges relate? How does the ungrounded GFCI react?
“In what scenario does the ungrounded GFCI trip? Does it trip during a lightning strike? Does it trip if the appliance plugged into it is short circuits?”
The GFCI monitors current balance between the neutral (white wire) and power conductor, if the current coming back on the neutral is unbalanced the circuit assumes that the imbalance is due to some kind of ground fault (current leaking to ground) and thus opens the power conductor de-energizing the circuit.
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Not sure about lightning but the sticker is there to tell the end user that the receptacle, although it has a third hole it is not grounded.
If the appliance is ungrounded the GFCI device will not trip if it faults internally to its metal parts. It will trip if a human becomes part of the circuit path by being grounded and touching the live metal parts.
Plugin style testers send a small amount of current to the EGC to initiate a ground fault. If the receptacle EGC is not connected to anything the GFCI receptacle will not trip. The TEST button on the GFCI device will work however because it does not need a connection to the EGC for it to operate.
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Thank you Robert.
So then there still could be a scenario where the human touches the energized appliance case but is not grounded and the GFCI does not trip?
Exactly, the standard for Class A GFCI protection is a trip setting of 5 mA (technically 4-6 mA). If the person is completely insulated then there won’t be 5 mA’s or more current flow for the device to measure and then trip.
What if the person is grounded when they touch it?
Hopefully if it’s functioning normally the GFCI device opens the circuit and they do not die. 
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1 yes
2 not if it is GFCI protected
3 if the grounded conductor is 'lost , unlikely but possible
You started by using terms correctly then mid-post started being vague in your questions
Both receptacles are grounded.
Lightning has nothing to do with it.
The only proper way to test a GFCI is with its test button.
I would disagree. The “Test Button” will properly test the GFCI Circuit, but only if the GFCI Receptacle outlet is properly wired in the first place. If the Installer of the GFCI Receptacle outlet mixed up the Line and Load, The test button will kill power to receptacles down stream but the GFCI Receptacle Outlet itself, will still have power. It is always important to use your tester on that First GFCI Outlet to see if it also is no longer energized after the Test button is pushed or after using the tester to trip the circuit.
I find a couple of these mis-wired every month, mostly on DIY homes, but have also found this on New Construction.
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I’m not sure why you’re seeing this in new construction, GFCI receptacles have been required for more than a decade to de-energize the face and all downstream receptacles if the line and load are reversed. Those would have to be some pretty old receptacles being installed in new construction.
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Interesting about the newer GFCIs that are “supposed to” not allow this…I would say the last one on new construction I had do this, (seamingly trip, but staid energised), was about 3 years ago. I’m wondering if there was some kind of other problem internally with the device?? (looks like the “stupid proof” change has been since about 2003) so yes the newer ones should not allow for this problem. Maybe what I found was one that had a manufacturing defect? and this why I will continue to check that GFCI Receptacle for power after tripping, not just those downstream.
I was not clear. The test button is the only way to know if the GFCI is operating as designed. Yes, you must use a lamp (any device) or in our case a handheld tester to verify all receptacles that are associated with the GFCI being tested are protected.
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The GFCI protecting a circuit which does not have an Equipment Grounding Conductor will not trip until the 5 milliamperes of leakage current actually occurs. A ground fault to a metal box; which were the only type in use when ungrounded electrical circuits were being installed; would energize the ground pin of a three wire receptacle installed in that box. Leakage current will not flow until something or someone makes contact with a metal cover plate or the portion of a portable device that is bonded to the grounding pin of the cord. A three wire vacuum cleaner is plugged into the receptacle with the energized current carrying conductor (the hot) faulted to the box. The metal surfaces of the vacuum are now energized. When the user touches the vacuum’s metal handle they get a momentary shock while the GFCI is opening the circuit. The “Startle effect” of that shock can still cause the person to react in a way that may injure them. If an Equipment Grounding Conductor were present in the circuit the GFCI would trip the moment the fault occured instead of when something or someone provided a pathway for the fault current to flow outside the circuit.
It is to prevent the other outlets from electrifying the shells of any portable tool that is plugged in that kind of circuit that the NEC forbids connecting Equipment Grounding Conductors of outlets extended from a circuit without an equipment ground.
–
Tom Horne
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