GFCI *breaker* failure modes?

[Don Y]

Hi Bud,

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?

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 <shrug>.

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)

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

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.

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

Kitchen is counter top receptacles.

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!

 

[ehsjr]

"bud--"

** Simple, very relevant fact.




** Possible.




** This one is different to your example.

http://www.fairchildsemi.com/ds/RV/RV4141A.pdf

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".

No injected current and there is a load present.

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

 

[Phil Allison]

"ehsjr"
Phil Allison:

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.

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

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

Load _terminals_ are shown, but there is no load
shown connected to them, nor is one needed.

** Rb is there to simulate a ground fault of 6mA.

There is
a _fault resistance_ shown, and that resistance completes
the circuit to make the thing oscillate.

** And that is whole NEW thing and contradicts "bud--".

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.

** 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

 

[Phil Allison]

"bud--"

Phil Allison wrote:

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.

** You are turning into a parrot..

Polly want a cracker ?

As Ed detailed, there is an injected current.

** There is plainly no current being injected.

The application circuit shows external loads that trip H-G and trip with a
N-G short,

** Yep, like I said there is a load.

And you are a fuckwit one trick phoney.



.... Phil

 

[Phil Allison]

"Mike Perkins"

If Neutral and Earth are connected on the premises, then Neutral and Earth
will be at the same potential,

** 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.

No they don't.

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

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.

** 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

 

[ehsjr]

Hi Ed,



See my back of napkin analysis as to why this can't be
what I'm seeing...

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

 

[Phil Allison]

"Mike Perkins"

"Mike Perkins"


Agreed.

** 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. "

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.

** 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

 

[bud--]

But only circuits feeding receptacles?
Yes

I.e., what about lighting
circuits?

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

Refrigerator?

Plugs into a receptacle.

Furnace, etc.? They are also likely (?)
to suffer from an arc fault...

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.

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

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

 

[bud--]

"bud--"

** You are turning into a parrot..

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

** There is plainly no current being injected.

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.

** Yep, like I said there is a load.

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.

And you are a fuckwit one trick phoney.

Everyone seems to understand except you.

 

[Don Y]

Hi Bud,

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

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

Plugs into a receptacle.

Ah, OK.

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

They are also likely (?)

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.

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

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

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?

 

[[email protected]]

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.

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

 

[Phil Allison]

"Mike Perkins"

I don't see how I've changed anything.

** The you really need to learn how to read.

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.

** No you didn't and several is not minimal.

The idea is that a faulty circuit is obvious before plugging in any
appliance.

** No it isn't.

Cos in 99.9% of cases, the N-E short will be inside an appliance !!!

You are clueless and have nothing to say - so please piss off.


.... Phil

 

[Don Y]

Hi Ed,

On 9/25/2013 6:15 PM, ehsjr wrote:

[attrs elided]

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.

Note that I can use relatively large loads without it tripping
(see <
So, I will try to probe the potential ON THE BLADES of the
load's plug in an attempt to see what sort of resistance is
present in the wiring at these loads (e.g., 1KW). Using
"earth" as my "0V" reference and a relatively high impedance
DVM (to avoid tripping the GFCI by this "measurement current").

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

That's tedious as the boxes are weatherproof (so, lots of
screws holding the weatherproof covers on OVER the receptacles).

Also, I would prefer to *see* the failure, hypothesize a cause
and then institute a remedy (even if that remedy is as simple
as cleaning the crud OR replacing the receptacles) and VERIFYING
the problem has "disappeared". I.e., to see a definite cause
and effect.

I've found my HiPot but the fuse has been removed and I don't
recall why I did that. But, know it can't be a good sign! (cuz
I have plenty of spare fuses!). So, I'll now have to sort out
the state of that tester, as well.

Sheesh! Nothing is ever easy!! But, hopefully, we won't see any
cold weather for another few months so I've got time to suss it out.

 

[bud--]

Hi Bud,



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

Circuits are usually mixed lighting and receptacle. I can't remember a
residential circuit that was just lighting.

But you could write a code change proposal to advance the march of AFCIs
to take over the world.

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

I don't believe the NEC allows cord connected furnaces or plug connected
furnaces.

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

A common reason to deny a code change proposal is that evidence has not
been presented that the proposal will make safer wiring. I think the
evidence for AFCIs has been minimal and anecdotal - not a good idea.
Improved safety will generally be in the future when new wiring becomes
old wiring.

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??

GFCI protection is required for residential kitchen counter top
receptacles.

There is no current requirement for AFCI residential kitchen protection.
I have read that it will be required in the 2014 NEC (whenever that
provision is accepted where you live).

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?

AFCIs don't replace GFCIs. GFCIs trip with 5mA ground fault, AFCIs with
about 30mA ground fault. Another question is whether GFCIs trip faster.

 

[ehsjr]

"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.

I never said a load is needed for a GFCI to detect a N-G short.
You must have missed the word "without" in what I wrote.

** Rb is there to simulate a ground fault of 6mA.

Correct, Rb simulates the fault. There is no load connected.

** And that is whole NEW thing and contradicts "bud--".

Not new at all. We've been discussing a N-G fault resistance
and a N-G short all along. It confirms what Bud said.

** 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.

Thanks. I know about GFCIs, but have no experience with RCDs.
I gather that RCD is the correct term to use when talking
about the Australian equivalent of what we call a GFCI.

Ed

 

[Phil Allison]

"ehsjr"

I never said a load is needed for a GFCI to detect a N-G short.
You must have missed the word "without" in what I wrote.

** You are an illiterate jerk.

Correct, Rb simulates the fault. There is no load connected.

** Funny how it is across A and N then......

Not new at all.

** Fraid it is new.

You need to learn to read sometime.

Thanks. I know about GFCIs, but have no experience with RCDs.

** Yawnnnnnnnnnn....

Remedial reading classe are available at your local Community College.

Remedial thinking is however another matter.



.... Phil

 

[ehsjr]

"ehsjr"

** You are an illiterate jerk.

Your opinion does not change the fact that you missed,
or did not understand, the word "without".

** Funny how it is across A and N then......

There is no "A" shown in the diagram. Rb is shown across
live and neutral and is identified in the datasheet text
as follows:
"Rb represents a normal ground fault resistance."

Read the datasheet text.

** Fraid it is new.

Fraid you're wrong. My post date/time stamped 9/22 at 3:48 AM
discusses, and is the first mention of, the RV4141A. Your first
post the mentions the RV4141A is stamped 9/24 at 6:38 PM

Both the datasheets mentioned show _TWO_ current transformers,
which bud mentioned and with which you disagreed.
To remind you, here's what you wrote in your post date/time
stamped 9/21 at 10:40 PM replying to bud:

First you quoted Bud: "There is a second current transformer
that tries to put a small common mode current in both the H
and N wire."

You replied" "** Hogwash."

In your post stamped 9/24 at 6:38 PM you quoted Bud
and responded as follows:

Bud said: "GFCIs have a second CT to immediately trip on N-G
shorts with no load."

Your reply was: "** This one is different to your example.

http://www.fairchildsemi.com/ds/RV/RV4141A.pdf"

A look at the datasheet in the url _CLEARLY_ shows _TWO_
current transformers, precisely what Bud was talking about.

You also said: " No injected current and there is a load present."

If your point is some quibble about the word "injected", Bud did
not use it - _you_ did. Bud's sentence was "There is a second
current transformer that tries to put a small common mode current
in both the H and N wire."

You have been proven wrong on the current issue, whether
you want to quibble with your own use of the word "injected"
or fail to recognize that inducing a current is done by that
transformer.

You need to learn to read sometime.
PKB



** Yawnnnnnnnnnn....

Remedial reading classe are available at your local Community College.

Try taking one - you need it.

Remedial thinking is however another matter.

Yes, you demonstrate that quite well, whenever someone
disagrees with what you've posted. And in the above, you
demonstrate it when someone thanks you for something you've
posted.

Reading what you write about electronics is interesting and
worthwhile, even if at times there may be some disagreement
with what you posted. However, when you post your opinions
of other posters, the value of what you write is zero.

Ed

 

[Phil Allison]

"ehsjr"

Your opinion does not change the fact that you missed,
or did not understand, the word "without".

** You missed the context entirely.

GFCIs simply do not *need* a second sense coil ( or a load) to detect NG
shorts.

You are an illiterate jerk.

There is no "A" shown in the diagram. Rb is shown across
live and neutral

** So it is a normal load.

You are an illiterate jerk.

Fraid you're wrong.

** You have missed the context.

Its is a another *method*, not involving the injection of 100Hz current.

You are an illiterate jerk.

First you quoted Bud: "There is a second current transformer
that tries to put a small common mode current in both the H
and N wire."

You replied" "** Hogwash."

** You have missed the context again.

You are an illiterate jerk.

A look at the datasheet in the url _CLEARLY_ shows _TWO_
current transformers, precisely what Bud was talking about.

You also said: " No injected current and there is a load present."

If your point is some quibble about the word "injected", Bud did
not use it - _you_ did. Bud's sentence was "There is a second
current transformer that tries to put a small common mode current
in both the H and N wire."

** You are an illiterate jerk.

You need to learn to read sometime.

Remedial reading classes are available at your local Community College.

Remedial thinking is however another matter.

Cos fucking nut case idiots like YOU are a dime a dozen.

**** off.

 

[ehsjr]

"ehsjr"


** You missed the context entirely.

GFCIs simply do not *need* a second sense coil ( or a load) to detect NG
shorts.

Your capacity to ignore what the datasheets show is awesome!

Ed

 

[[email protected]]

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

Neutral and Earth are NOT linked at the premises.

This is only sometimes true. Older installations usually have
neutral linked to earth only at the substation transformer and not
at the premises (TN-S). Gas and water service pipes are bonded
to the incoming mains earth near the entry to the premises.
However, many properties now have "protective multiple earthing"
(PME or TN-C-S) supplies where the neutral is earthed at
multiple points in the distribution system. In a PME
installation the earth wiring within the property is linked to
neutral at the point where the incoming two-core supply cable is
terminated, just before the meter. Gas and water service pipes
are bonded to that earth/neutral point. In newer properties
both gas and water are supplied through plastic pipes, so in
this case only the internal plumbing is connected.

AC outlets are wired in a loop.

Usually, but not always. Radial circuits are allowed.

John