The test button merely connects the hot to the GFCI's ground reference, so no earth ground is needed to test operation. But a plug- in GFCI tester will work, whether or not the GFCI is earthed.
Here's National's document for their old LM1851 GFCI chip:
Absolute nonsense, as GFIs measure only the imbalance of currents in the hot and neutral lines that pass through their current sensing transformers. No GFI can require an earth ground for proper operation and still meet UL standards.
Right except it is line side hot to load side neutral (or vice versa).
Nope. The GFCI outlet circuit makes no connection to "ground". The test button connects a resistor from the hot wire ahead of the current transformer to the neutral downstream from the current transformer (or vice versa) resulting in a current through the transformer only on the neutral wire.
A plug-in tester connects a resistor from hot to ground. Since ground is not connected to anything a plug-in tester will not work.
Interesting that the circuit (fig 2) does not show the test button that is on all GFCIs.
Also interesting that the feature that causes an immediate trip if there is a downstream N-G connection only adds 2 parts.
Downstream outlets are also tagged "GFCI protected".
Avoid connecting the outlet grounds together on downstream grounded outlets where a ground is not present.
Seems like that should have been obvious to Twayne. If 3 wire plugs were not allowed the NEC would require a 2 wire GFCI outlet - which it doesn't. The NEC explicitly allows 'grounded outlet' GFCIs on 2 wire circuits, and as you said above, allows the GFCI to protect conventional grounded receptacles downstream.
Its them PEX fanatics on this newsgroup that have ruined it for the rest of us.
Well, 406.3(B) of the 2008 NEC states: "Receptacles and cord connectors that have equipment grounding conductor contacts shall have those contacts connected to an equipment grounding conductor". And
406.3(D), the section that deals with using GFCIs on circuits without equipment ground, does not appear to override 406.3(B). So I agree the situation is confusing and the intent is not clear.Cheers, Wayne
Set Lawyer-Speak Mode =3D True
A 3 prong plug is typically connected to a cord which has an equipment grounding conductor within, therefore the "cord connector" portion of
406.3(B) is satisfied.Once this cord is plugged into a 3 prong receptacle, the receptacle's equipment grounding conductor contact will be connected to the cord's equipment grounding conductor, this satisfiying the receptacle portion of 406.3(B). Prior to the insertion of the plug, the grounding hole in the receptacle is nothing more than an extra hole since it's not attached to anything. If it's not attached to an equipment grounding conductor, it isn't a equipment grounding conductor contact because the code says it isn't.
Set Lawyer-Speak Mode =3D False
That clears it up, now, doesn't it?
406.3-B "...shall have those contacts connected to an equipment grounding conductor." "Exception No. 2: Replacement receptacles as permitted by 406.3-D" 406.3-D replacement of receptacles shall comply with D-1,2,and 3 as applicable 406.3-D-3 "Non-Grounding Type Receptacles. Where attachment to an equipment grounding conductor does not exist in the receptacle enclosure, the installation shall comply with D-3-a, D-3-b, or D-3-c." 406.3-D-3-b allows GFCIs to be used. The GFCI ground terminal is not allowed to be extended to downstream receptacles 406.3-D-3 allows grounding receptacles to be used where downstream from a GFCI. A ground is not allowed to be connected between the receptacles.
They do not conflict.
The intent is clear. (A rare miss.)
Whoops, I completely missed that. Thanks for the catch.
Cheers, Wayne
But I've tried it with a Hubbel (Shock Shield 3-outlet) plug-in GFI with its ground prong retracted and a Sears branded Leviton wall outlet GFI connected to the AC through a 2-wire cheater cord. I believe both used General Instruments GFI chips.
OK; since we're clarifying, lets be a tad more accuate. I only add this for clarification, no other reason. Many homes have a mix of such 2 and 3 wire installations and it's easy to misunderstand some things.
A GFCI is for "safety", not people. Kind of minor on the surface, but important in the altogether. Also, lack of a ground for equipment that needs it -could- lead to lethal shock situations where under a single fault condition it could lead to anything from shock to fire.
Well, not from "within the device" but from any point in the entire circuit on the Load side of the GFCI; wire, connections, equipments, etc.. Sufficient leakage anywhere will trip the GFCI. It simply measures and compares hot/neutral current, as you said.
If there is anything anywhere, not just within the device, that causes a differential, the gfci will trip.
NEC definitely recommends AGAINST doing so, and requires the markings. In addition, NEC is not the final word; NEC is only minimum requirements. The local Code Enforcement Office will have the final say on whether a 3-prong outlet can be used without an earth ground connection. Here such 2-wire methods with 3-wire outlets etc. are specifically verboten in the kitchen, bathroom and outbuildings. Many people forget that it's the local codes that must be satisfied; the NEC may be but one component of the electrical requirements. The NEC/local codes would reall only come into the picture if it was new work. e.g. when I added a ckt, all they checked was the ckt, and nothing in the rest of the house. Some localities however insist that if you touch the wiring at all the whole building has to be brought up to code. It varies all over the map.
Nah, no serious corrections were needed. Just had time to do a little further clarification, so did.
Regards,
Twayne`
Whatever that means.
The 5mA trip level on a GFCI is for people.
Some other GFIs (including most AFCIs) trip on a ground fault of 30mA. That is for the protection of equipment or fire.
That, of curse, is what the GFCI is for.
Cite.
Where. There would be no electrical changes in those locations - extremely counterproductive.
You forgot to clarify that your previous post was wrong and Derby was right.
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