GFCI *breaker* failure modes?

** Simple, very relevant fact.

** Possible.

** This one is different to your example.

No injected current and there is a load present.

** It does matter.

It's how all types of GFCIs work.

Not just ones that comply with the latest UL943 spec.

And you are a one trick phoney.

.... Phil

Meet my grandfather... :>

Here, the water pipe enters at one end of the house while the panel is sited at the other end. I.e., the panel grounds the plumbing, not the other way around.

Meter is at the street so there's gobs of subterranean pipe between here and there. OTOH, water softener's are commonly encountered as soon as the pipe enters the premises. Hence the bonding across the softener if you wanted to rely on the water supply for earth.

Yup. Though I see latest plumbing code requires 1" copper for main.

*Everywhere*? I.e., every circuit is either AFCI or GFCI protected? Lighting circuits? Furnace? ACbrrr? That can get expensive!

Kitchen (small appliance circuits) have been GFCI for ages. Though the rest of the kitchen was exempt (dishwasher, disposal, etc.)

But, at the end of the day, you are at the mercy of your local inspector and *his* understanding of the Code. Most places don't provide a means of "appeal", etc. Which can be amusing if inspector A says X and followup visit from inspector B says Y!

My point is that even "experts" are often unsure as to what the code actually says for any given situation. Just like two lawyers reading the same contract can come to two different conclusions as to how it applies in a specific case.

Finding dividers wasn't the problem. Deciding if it was *required* was the issue, in my case.

If there is a metal water service it is being used as an earthing electrode. If you connect to the water pipe why isn't it being used as an earthing electrode?

If the water service pipe is plastic, interior metal water pipes are "bonded" with similar methods.

New installations require the connection to be within 5 feet of where the water pipe enters the building. In the past the water pipe was often used as a conductor.

120V, 15 and 20A receptacles in "dwelling unit family rooms, dining rooms, living rooms, parlors, libraries, dens, bedrooms, sunrooms, recreation rooms, closets, hallways, or similar rooms or areas ..."

The branch circuit is protected, not just the receptacle.

Kitchen is counter top receptacles.

IMHO experts are not often unsure. That is the point of "lawyer language".

The relevant fact is what was being discussed was Don's GFCI in the US.

"Outside the US" is not relevant to Don's questions.

It is the IC Ed talked about. I provided the link.

As Ed detailed, there is an injected current. What is the "Grounded Neutral" CT for?

As is quoted above "GFCIs have a second CT to immediately trip on N-G shorts with no load."

The application circuit shows external loads that trip H-G and trip with a N-G short, which Ed explained. The IC trips on a N-G short through a common mode current imposed on H and N, just as I wrote.

Everyone agrees a load will trip a GFCI with a N-G circuit fault.

What I wrote is right, as shown by both IC app notes.

Your "hogwash" is hogwash.

You are remarkably dense when you want to be.

The local code (30+ years ago) required a grounding rod at the service entry. Apparently *many* homes were plumbed with some wacky plastic pipe (*not* PVC). There was no requirement to include bonding straps across water softeners (which are very common here) so you can't rely on continuity from "pipe through soil" *into* the house. Likewise, no bonding straps across hot water heaters.

We have a copper main; some of the neighbors have PVC mains; yet all the houses were built within a couple of years of each other .

Half the houses have pressure reducing valves on the water main (again, no bonding requirement). AFAICT, *none* have expansion tanks downstream of said PRV's. Everything seems to be pretty much "hit or miss" (actually, I think these homes were in The County when built so there might be some portion of the explanation, there)

But only circuits feeding receptacles? I.e., what about lighting circuits? Refrigerator? Furnace, etc.? They are also likely (?) to suffer from an arc fault...

What about *other* receptacles in the kitchen? I.e., those that weren't previously GFCI requirements?

I'll just have to pick up a newer edition of code book.

Thx!

It shows the 2 CT's that he is talking about, and that it trips in the presence of an N-G short with or without a load. See figure 3 on page 6, and the explanation of how a N-G short is detected on page 5. There are 2 current transformers shown on the schematic: one is labeled "Sense Transformer" and the other is labeled "Grounded Neutral".

Load _terminals_ are shown, but there is no load shown connected to them, nor is one needed. There is a _fault resistance_ shown, and that resistance completes the circuit to make the thing oscillate. That oscillator runs at a frequency determined by the grounded neutral coil and capacitor C4, meaning there has to be current in that coil. Read the datasheet in the url you posted.

I can tell you from experience that our (USA) GFCIs will trip immediately if the neutral is shorted to ground on the load side with or without a load connected.

I suppose that your GFICs are different, but having no experience with Australian GFCI's I don't know.

Ed

"ehsjr" Phil Allison:

** GFCIs trip with NO load when N and E are shorted.

No load is needed, only a tiny N to E voltage difference.

** Rb is there to simulate a ground fault of 6mA. ** And that is whole NEW thing and contradicts "bud--". ** GFCIs ( or RCDs) all trip with NO load when N and E are shorted.

No load is needed, only a few mV of N to E voltage difference.

... Phil

** You are turning into a parrot..

Polly want a cracker ?

** There is plainly no current being injected. ** Yep, like I said there is a load.

And you are a f****it one trick phoney.

... Phil

If Neutral and Earth are connected on the premises, then Neutral and Earth will be at the same potential, so a N-E short won't show up unless the GFCI has this extra transformer to induce a common mode voltage in the Live and Neutral. Only then will a N-E short trip the GFCI.

No they don't. I've have known RCDs to randomly trip after a significant length of time (minutes) where a UK RCD load was subject to a N-E short. The whole point of this extra winding is to put a common mode voltage on Live and Neutral to detect such shorts quickly.

If it wasn't for the OP measuring N-E resistance, I would have suspected a N-E short.

--
Mike Perkins 
Video Solutions Ltd 
www.videosolutions.ltd.uk

"Mike Perkins"

** Completely wrong !!!!

Neutrals are current carrying conductors while Earths are NOT !!

Soon as there is ANY load current in the Neutral, a voltage difference is created.

FYI:

If I take a AC amp meter and probe from N to E on an outlet in my kitchen - it reads 0.75A.

If I turn on a 2kW room heater, the reading goes up to 2.6A !!

There is no GFCI installed in the premises, Australian rules only require them for installations done after the date of the rule. However, if I use a plug-in GFCI, it trips instantly when N and E are linked at the output.

These are NOT strange happenings but **completely normal** things.

** Yes they do !!!!!!!!!!!!

** False argument - anyone can *claim* to have seen any damn thing.

FYI:

The UK uses deterrent wiring practices to the USA, Australia and most other places

Neutral and Earth are NOT linked at the premises.

AC outlets are wired in a loop.

Appliance plugs have fuses in them.

AFAIK - all unique to the UK.

.... Phil

I'd like to see the analysis - is there a date/time stamp where I can find it in the thread?

And setting that question aside, it's a good thing if you've ruled out the possibility of a partial N-G short. You can try some measurements, if you want to:

Hot ---[R1]---[Load]---[R2]---Neutral

Pick a load that doesn't cause it to trip, and measure the voltage across each R. Say the load is 60 watts and you use 1 ohm, 5 watt resistors. With ~ 1/2 amp you'll read ~500 mV across each resistor and each mV of difference represents 1 mA. If the circuit can run 120 watts without tripping, so much the better, as the difference between Vr1 and Vr2 will be greater. Your measurement will depend upon the exact resistance of each resistor, but you can account for that with math. eg R1 is say 1.001 ohms and R2 is .999 ohms so Vr1/1001 should equal Vr2/.999 Any difference means there is another path for current somewhere. If there are multiple j-boxes, you can cut the circuit in half by disconnecting in the middle, to see if that gets rid of the difference.

If it was me, I'd open every outdoor j-box on that circuit and clean out the crud in them before trying measurements.

Ed

Agreed, that is the idea.

Agreed. That is the reason why US GFCIs have the extra coil, to trip when there is no load.

You implied later in your post that in Australia Neutral and Earth are connected on the premises, if that is correct I would be wondering why I have a 0.75A current flow between Neutral and Earth when no current is flowing in that circuit.

--
Mike Perkins 
Video Solutions Ltd 
www.videosolutions.ltd.uk

** So you have completely backed down for your previous nonsense:

" If Neutral and Earth are connected on the premises, then Neutral and Earth will be at the same potential, so a N-E short won't show up unless the GFCI has this extra transformer to induce a common mode voltage in the Live and Neutral. Only then will a N-E short trip the GFCI. "

** There is no current from the particular outlet, but any appliance in the premises passes current down the neutral - creating a voltage difference to earth seen at all outlets on the same run. Just one, very small load is enough - even suppression caps wired across A and N would do the job.

The UK situation is quite different, having outlets wired in loops and no N-E link at the entry largely defeats the above process - despite which, UK authorities see no need for special measures to ensure that a N-E short causes tripping.

Why the Yanks alone are so anal about it is still a mystery.

.... Phil

Yes

No AFCI protection required if there are no receptacles on the circuit.

Plugs into a receptacle.

Most likely arcs are receptacle circuits and the loads that are plugged in.

Furnaces very likely have metal-encased wiring at the furnace where a fire is real unlikely.

But wait a few years. The NEC seems to be adding every year.

My intent was to say that GFCI protection is only required for kitchen counter top receptacles.

I'm sorry. Logic appears to be to complicated for you.

You forgot to answer: "What is the 'Grounded Neutral' CT for? "

With minimal electronics background you could read the app note and see that the CT injects a common mode current. Ed also explained it. As Ed and the app note explain, the current is created by oscillation. You seem to be the only person who can't understand.

As the app note shows the GFCI trips on H-G current.

And it trips on a N-G short with no load because of the injected current. Ed also explained that. Ed's point then was that the N-G short has to be relatively low resistance.

Everyone seems to understand except you.

I don't see how I've changed anything. I have always said that zero or minimal ground current should flow for circuits that have Neutral and Ground connected at their source, ie at the distribution board.

The idea is that a faulty circuit is obvious before plugging in any appliance. That way the appliance doesn't get blamed, like the drill in the OP's case.

One advantage of being anal about GFCIs and RCDs is that one can become less anal about the rest of the system. In the UK many rules about Earthing become relaxed as soon as wiring is protected by GFCIs and RCDs. It can save a lot of bother and time.

--
Mike Perkins 
Video Solutions Ltd 
www.videosolutions.ltd.uk

Seems a glaring hole. Lighting fixtures can have similar problems with arcing, etc.

Ah, OK.

Here, furnace ALSO plugs into a receptacle. Though I've lived places with, e.g., oil fired furnaces that were hardwired.

Yup. And this is to be expected. Goal is to *reduce* hazards. The more "likely causes" uncovered, the more regs fall into place.

So, AFCI required for those now, as well? Or, are you saying *only* GFCI required? Though AFCI would be required for the *other* outlets in the kitchen??

I.e., if I determine the GFCI breaker here to be toast, plan on replacing it with AFCI breaker (outdoor branch circuit). And, consider purchasing AFCI replacement breakers for the other GFCI circuits?

I meant to include, that where Earth and Neutral are shorted, if there is no current load on the circuit in question, no Earth current should flow.

--
Mike Perkins 
Video Solutions Ltd 
www.videosolutions.ltd.uk

The same is true in the US. Existing structures, without grounded outlets, can be code compliant when protected by GFCIs.