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Working in an 80+ year old house in which the circuit wiring is not necessarily always logical and there are no ground wires. One circuit runs to two outlets in the study on the first floor, then up to outlets in bedrooms on the second floor.

With a little bit of work, I managed to run a ground wire to the first outlet in the circuit, in the study. I then installed a GFI outlet there. (I think it's the first in the circuit, because when I trip the GFI all the other outlets lose power.)

When I plug a GFI tester into the GFI outlet, it trips correctly. However, when I plug a GFI tester into any of the downstream outlets, they do not trip the GFI outlet.

As I said, all the other downstream outlets do not have a ground wire. So, is this expected behavior? Are the downstream outlets still GFI protected? (And so I can still label them as such?)

Circuit Diagram

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  • Wait, is that diagram accurate? Do you really have outlets with holes for grounded plugs and no ground wires? That sounds like a significant safety concern.
    – nick012000
    Nov 9, 2021 at 7:01
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    @nick012000 Ungrounded outlets are extremely common and protecting them with a GFCI upstream is also extremely common. It is safe and allowed by the NEC.
    – TylerH
    Nov 9, 2021 at 14:41
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    @nick012000 The upstream GFCI takes care of the human-safety issues. However the groundless outlets do nothing to protect equipment from ESD. Therefore they must have stickers "GFCI Protected" and "No Equipment Ground" per 406.4(D) and 110.3(B) -> 8(C) in the UL-approved instructions that came with your GFCI. Nov 9, 2021 at 22:59
  • @Harper-ReinstateMonica The GFCI on a different outlet protects you from your toaster's metal casing becoming electrified because it doesn't have a ground wire?
    – nick012000
    Nov 9, 2021 at 23:13
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    @nick012000 You asked if it "protects you" - yes, it does. The key is the GFCI protection. Nov 9, 2021 at 23:35

5 Answers 5

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The other answers state the facts, but here is (I hope) a bit more explanation:

A ground fault that a GFCI interrupts, does not necessarily have to do with ground per se. A GFCI watches hot and neutral to make sure they have the same amount of current. Any imbalance means some current is going someplace it shouldn't go. That can include:

  • Ground wire
  • Through a person to physical ground
  • Directly to physical ground - e.g., metal case on a wet floor

A GFCI tester takes some current from Hot and sends it to the Ground wire. Sending it through a person deliberately is never a good idea, and it is hand-held so it isn't touching ground, so the Ground wire is the only thing left. This is done through an appropriately sized load (probably just a simple resistor) so that the current involved is large enough to trip the GFCI but small enough to be relatively safe and most definitely small enough that it won't trip a regular breaker. Stick a plain wire into Hot and Ground and you will trip GFCI, but you'll also trip the regular breaker (hard to say which would go first) and possibly hurt yourself and start a fire, so don't try that

But if the ground pin is not connected then the GFCI tester tries to send current from Hot to Ground but it never gets anywhere - essentially the same as having a hot wire sit open in the air. The GFCI doesn't trip, but no harm is done, and it does not in any indicate that there is a problem with the GFCI.

Normally, a 3-wire receptacle can't be installed without the ground pin properly connected to a ground. However, an exception is allowed if and only if there is a GFCI upstream. The reasoning is that the very same type of safety problems that a ground wire protects - a short-circuit routing power from hot to ground - will also be protected by a GFCI when it spots the current mismatch. In this setup, if the power doesn't go anywhere, such as a short from hot to a metal appliance cabinet, the GFCI won't initially trip. But as soon as someone touches it and some of the current starts to go into the person, the GFCI will detect the imbalance and trip, providing comparable safety (actually often much better) to what a traditional ground wire would provide.

The one exception is static electricity, electrical noise and other uses of the ground wire. These will not be protected in this setup because the ground wire doesn't actually go to the ground. Not much of a safety problem, but it can be a potential sensitive equipment damage problem. As a result, these ungrounded 3-pin receptacles are supposed to be labeled to indicate that they are GFCI protected but not grounded.

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    Correct. And that ground wire gets used by surge protectors, so if you have one plug it into that first outlet.
    – Jon Custer
    Nov 9, 2021 at 17:27
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Not tripping an ungrounded receptacle should be expected. Every gfci tester I have seen depends on the ground to create the imbalance of current between the hot and neutral that the ground fault receptacle senses.

If the downstream receptacles go dead when you press the test button on the upstream receptacle then you are good to go and you should install the stickers that come with the gfci receptacle as the instructions say (and to comply with the NEC).

Usually the tester instructions are vague. They will say to verify that the lights indicate proper wiring and then (step 4 in the above link) "if the receptacle indicates correct wiring depress the gfi test button". They aren't always clear that the following step is inaccurate when proper pattern is not indicated.

Please check the instructions that come with your tester to verify.

If you wish to further test you could get a grounding adapter plug and connect the little tab with a piece of wire to an actual ground, then the ground light on the tester will light and the test button will trip the gfci if functioning properly.

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    If the downstream receptacles [that were live] go dead when you press the test button. +1
    – Mazura
    Nov 9, 2021 at 3:53
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This is typical if you have not correctly wired the GFCI feed to the LINE terminals and the downstream outlets to to the GFCI LOAD terminals. Can you provide an actual photograph of the wiring at the GFCI?

However, it may be due to the GFCI tester depending on a ground connection to produce its "test ground fault." And the fact that downstream outlets are going out when the GFCI is tripped suggests that you do have them correctly wired to LOAD.

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So, is this expected behavior? Are the downstream outlets still GFI protected?

Yes, completely normal and expected.

The GFCI takes care of human safety. This does nothing to help equipment "ground" for ESD protection, hence the labels.

enter image description here

If you really want to do a bang-up job of testing it, then get one of these 3/2 prong "cheater plugs" and run a looooong wire off the ground flange on it. Take that wire to the service panel chassis or house's Grounding Electrode wire. This will give the tester the ground it needs to work. Only use it for this; it's dangerous otherwise!

(And so I can still label them as such?)

Can you? It's mandatory. NEC 406.4(D)(2) requires the "No Equipment Ground" markings. NEC 110.3(B) and instructions 8(C) require the "GFCI Protected" markings even on grounded protected outlets.

No need to use the flimsy/ugly blue stickers, you can fabricate the labels any way which is not hand-written. I like P-touch/Brother label makers on white cover plates.

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  • Wonders why the down vote
    – FreeMan
    Nov 10, 2021 at 13:39
  • Probably saw the cheater and didn't read. Or someone was reading on iOS, where the touch zones for downvote are enormous. Nov 10, 2021 at 17:06
  • As an Android user, I find your statement about iOS rather amusing. ;)
    – FreeMan
    Nov 10, 2021 at 17:18
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The GFCI tester lets a small current flow between Live and Earth to simulate a fault, and that should trip the GFCI.

If the socket does not have an Earth wire, then the tester won't work.

If an appliance leaks current to its chassis, and the chassis is earthed through the socket, then the RCD will trip before someone touches the dangerous appliance, which prevents an accident.

However, if the appliance is not earthed because the wall socket doesn't have a connection to Earth, then that can't happen. So the RCD will only trip when someone touches it and acts as an Earth conductor. In this case, it doesn't prevent the accident, but makes it more survivable.

It's not exactly wise to install sockets which allow someone to plug in an appliance that requires Earth, while it's not actually connected in the socket...

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    It's not exactly wise to install sockets which allow someone to plug in an appliance that requires Earth, while it's not actually connected in the socket... Except in the US it is allowed, provided their is a functioning GFCI. Nov 8, 2021 at 19:22
  • If the equipment needs ground for safety reasons (unlikely... hospital? Safety-critical software?) then UL would require the manufacture to state this requirement in the equipment labeling with further discussion in the instructions, all of which are also approved as part of the UL Listing. You must follow this labeling/instructions per 110.3(B). Nov 9, 2021 at 23:03
  • IEC Class 1 appliances do not have double insulated construction and must be earthed. Class 2 appliances do not need Earth so they don't have Earth prong on the plug. Sockets are incompatible by design to prevent a class 1 appliance with Earth prong on the plug to be plugged into an unearthed socket without Earth hole. If US code allows that, then it's ridiculous. I wouldn't be surprised though.
    – bobflux
    Nov 10, 2021 at 8:23
  • @bobflux If provided with 6mA ground fault protection the NEC does allow replacement of existing ungrounded receptacles with receptacles with a hole for the equipment ground and on circuits installed before the adoption of the equipment ground requirement. We are required to label them "No Equipment Ground", and there is an oft ignored list of appliances in NEC 250.114 that require a connection to the equipment ground that we are trusted to not plug into those ungrounded receptacles. Nov 10, 2021 at 14:03
  • Your RCDs are 30 mA devices, while our GFCIs are 5 mA devices. Makes a difference.
    – Ecnerwal
    Nov 10, 2021 at 14:31

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