PeterD wrote:
On Mon, 23 Nov 2009 18:38:47 -0700, D Yuniskis
wrote:


This is how GFCI breakers work -- they watch for current "leaking"
off to ground someplace other than in the "return" conductor.

No they don't. They look for imbalanced current flow between the two
conductors.

Gee, isn't that what I *said*? How do you get an imbalance if
current isn't *leaking* off to ground someplace other than
in the "return" conductor?

On Fri, 27 Nov 2009 17:40:49 -0700, D Yuniskis
wrote:

PeterD wrote:
On Mon, 23 Nov 2009 18:38:47 -0700, D Yuniskis
wrote:


This is how GFCI breakers work -- they watch for current "leaking"
off to ground someplace other than in the "return" conductor.

No they don't. They look for imbalanced current flow between the two
conductors.

Gee, isn't that what I *said*?

No, you didn't.

How do you get an imbalance if
current isn't *leaking* off to ground someplace other than
in the "return" conductor?

Re-read your post.

PeterD wrote:
On Fri, 27 Nov 2009 17:40:49 -0700, D Yuniskis
wrote:

PeterD wrote:
On Mon, 23 Nov 2009 18:38:47 -0700, D Yuniskis
wrote:


This is how GFCI breakers work -- they watch for current "leaking"
off to ground someplace other than in the "return" conductor.
No they don't. They look for imbalanced current flow between the two
conductors.
Gee, isn't that what I *said*?

No, you didn't.

How do you get an imbalance if
current isn't *leaking* off to ground someplace other than
in the "return" conductor?

Re-read your post.

I don't have to re-read it -- I *wrote* it!

A GFCI is nothing more than a tiny transformer with
"sense electronics" as its "load". The primary to the
transformer is the circuit being monitored. *BOTH*
conductors pass through the transformer.

Since an alternating current generates a magnetic field,
that field couples *through* the transformer to the
*secondary* of the transformer -- which is the "sense
electronics". The field generated by the primary is
a function of the *net* current flowing through the
primary "winding" (winding can often be confusing in this
context as it is usually just a "single turn" -- as such,
it doesn't even go completely *around* the transformer's
core!).

All of the current flowing *to* the INTENDED load (remember,
the GFCI can also see an *unintended* load!) goes through the
supply/hot lead, through the transformer's primary. All
of the current *returning* from the load passes through the
neutral/return conductor *also* through the transformer's
primary.

If any of the supply current has "leaked" away via some
other path (to "ground") -- like through a person's body -- then
the current to and current from will not be equal. As
such, the magnetic fields generated by each conductor won't
*perfectly* cancel out. As a result, some energy will be
coupled across the transformer's core to its secondary.

You can have a *lot* of gain across the transformer since
the secondary doesn't need much power to function. As such,
you can look for very small "leaks" even in circuits carrying
very *large* currents! I.e., aside from the physical size of
the transformer and the primary conductors passing through
it, a GFCI for a 1000A circuit is essentially the same as one
for a 20A "household" circuit.

(N.B. this would not be the case if you tried to *directly*
measure the individual currents -- e.g., resistively -- and
form the difference -- i.e., comparison -- algebraically)

If you've ever examined a GFCI circuit breaker, you will note
that it isnt the simple "two terminal" device of a regular
(non GFCI) breaker. This is because the GFCI breaker has to
have an additional "ground" connection (which a regular
breaker doesn't need) usually implemented with a short pigtail
(that you mechanically fasten to the panel's ground).

GFCI *outlets* are dogs. They work the same way but are
usually built of lesser quality components. Also, they
are subject to more abuse (each time an appliance is
plugged/unplugged). And, are often exposed to more
environmental extremes than a GFCI breaker in a panel box.

Also, note that there is no way a (typical) GFCI can "test
itself" to determine that it is (likely) operational. So, a
failure in the sense electronics can cripple the protection
feature in a way that is not obvious to the user (i.e., the
circuit still supplies "unprotected power").

Note that a GFCI offers no protection against an unintended
load directly across the hot + neutral. I.e., if you wear
rubber soled shoes (which is advisable when working with
electricity) and accidentally touch hot *and* neutral,
the circuit will gladly deliver its full rated capacity
*through* your body -- as if you were a light bulb! :
OTOH, if you did NOT have rubber soled shoes on (or had
some *other* path to "earth"), the GFCI *would* protect.
(i.e., don't fall victim to the false sense of security
that a GFCI protected circuit is somehow *safer* than
a regular circuit!)

Anything else you need to know? Wanna check my spelling?
Or, my grammar??

D Yuniskis wrote:

PeterD wrote:

On Fri, 27 Nov 2009 17:40:49 -0700, D Yuniskis
wrote:

PeterD wrote:

On Mon, 23 Nov 2009 18:38:47 -0700, D Yuniskis
wrote:


This is how GFCI breakers work -- they watch for current "leaking"
off to ground someplace other than in the "return" conductor.

No they don't. They look for imbalanced current flow between the two
conductors.

Gee, isn't that what I *said*?


No, you didn't.

How do you get an imbalance if
current isn't *leaking* off to ground someplace other than
in the "return" conductor?


Re-read your post.


I don't have to re-read it -- I *wrote* it!

A GFCI is nothing more than a tiny transformer with
"sense electronics" as its "load". The primary to the
transformer is the circuit being monitored. *BOTH*
conductors pass through the transformer.

Since an alternating current generates a magnetic field,
that field couples *through* the transformer to the
*secondary* of the transformer -- which is the "sense
electronics". The field generated by the primary is
a function of the *net* current flowing through the
primary "winding" (winding can often be confusing in this
context as it is usually just a "single turn" -- as such,
it doesn't even go completely *around* the transformer's
core!).

All of the current flowing *to* the INTENDED load (remember,
the GFCI can also see an *unintended* load!) goes through the
supply/hot lead, through the transformer's primary. All
of the current *returning* from the load passes through the
neutral/return conductor *also* through the transformer's
primary.

If any of the supply current has "leaked" away via some
other path (to "ground") -- like through a person's body -- then
the current to and current from will not be equal. As
such, the magnetic fields generated by each conductor won't
*perfectly* cancel out. As a result, some energy will be
coupled across the transformer's core to its secondary.

You can have a *lot* of gain across the transformer since
the secondary doesn't need much power to function. As such,
you can look for very small "leaks" even in circuits carrying
very *large* currents! I.e., aside from the physical size of
the transformer and the primary conductors passing through
it, a GFCI for a 1000A circuit is essentially the same as one
for a 20A "household" circuit.

(N.B. this would not be the case if you tried to *directly*
measure the individual currents -- e.g., resistively -- and
form the difference -- i.e., comparison -- algebraically)

If you've ever examined a GFCI circuit breaker, you will note
that it isnt the simple "two terminal" device of a regular
(non GFCI) breaker. This is because the GFCI breaker has to
have an additional "ground" connection (which a regular
breaker doesn't need) usually implemented with a short pigtail
(that you mechanically fasten to the panel's ground).

GFCI *outlets* are dogs. They work the same way but are
usually built of lesser quality components. Also, they
are subject to more abuse (each time an appliance is
plugged/unplugged). And, are often exposed to more
environmental extremes than a GFCI breaker in a panel box.

Also, note that there is no way a (typical) GFCI can "test
itself" to determine that it is (likely) operational. So, a
failure in the sense electronics can cripple the protection
feature in a way that is not obvious to the user (i.e., the
circuit still supplies "unprotected power").

Note that a GFCI offers no protection against an unintended
load directly across the hot + neutral. I.e., if you wear
rubber soled shoes (which is advisable when working with
electricity) and accidentally touch hot *and* neutral,
the circuit will gladly deliver its full rated capacity
*through* your body -- as if you were a light bulb! :
OTOH, if you did NOT have rubber soled shoes on (or had
some *other* path to "earth"), the GFCI *would* protect.
(i.e., don't fall victim to the false sense of security
that a GFCI protected circuit is somehow *safer* than
a regular circuit!)

Anything else you need to know? Wanna check my spelling?
Or, my grammar??
That's a very good run down

Btw.
there are Self testing GFCI's..
http://www.hubbell-wiring.com/Press/PDFS/H5185.pdf

We use these extensively. Coast more, but what the hell.

And those that get a little confused with the AGFCI units
which are mostly in the modern GCFI receptacle, just not
stated. Most don't know the difference.

Those that don't have U-ground corded devices get confused when they
still see their GFCI trip just from sliding in the
plug. This only happens with the newer GFCI's that include the arc fault
detection along with the ground fault current sense.

I just love it when high powered R.F. disturbances trip those lovely
AGFCI and AFB units

I also like it when the installer removes what looks like excess
neutral wire that's in a coil. by by RF choke. I haven't looked in a
code book lately how ever, Since it's not designed to teach those about
electricity, but just follow some guide lines for safety, I don't think
there is an assert about the coil being present. This is done via the
manufacturer for noise amuity. Not all may suggest to do this how ever,
if you see it packaged in a coil, bets are, you should keep it that way
or as much as possible. We have some Square-D line that will false
trigger if you remove that coil form, in the plant.

Jamie wrote:
D Yuniskis wrote:

Also, note that there is no way a (typical) GFCI can "test
itself" to determine that it is (likely) operational. So, a
failure in the sense electronics can cripple the protection
feature in a way that is not obvious to the user (i.e., the
circuit still supplies "unprotected power").

Btw. there are Self testing GFCI's..

Really? I stand corrected (I will have to chase down the link
to see how they work). Presumably, they test the sense
electronics *while* disabling the "trip" function? (I
can't see how else they could operate as you surely wouldn't
want the circuit to open each time it tested itself : )
In which case, I guess they hope that the circuitry that
inhibits the trip never fails! :

http://www.hubbell-wiring.com/Press/PDFS/H5185.pdf

We use these extensively. Coast more, but what the hell.

What sort of cost premium? Are they required for use in
certain applications (medical, etc.)? Or, is it just
"a nice feature to have"?

And those that get a little confused with the AGFCI units
which are mostly in the modern GCFI receptacle, just not
stated. Most don't know the difference.

Those that don't have U-ground corded devices get confused when they
still see their GFCI trip just from sliding in the
plug. This only happens with the newer GFCI's that include the arc fault
detection along with the ground fault current sense.

Ah, OK. So, I assume most modern electronic loads (i.e.,
things with line switchers in them like PC's) trip these
often?

I just love it when high powered R.F. disturbances trip those lovely
AGFCI and AFB units

RF as in *radiated* (not *conducted*)? Like someone keying
a transceiver nearby? How close do they have to be (i.e. does
this cause grief in actual *practice*)?

I also like it when the installer removes what looks like excess
neutral wire that's in a coil. by by RF choke. I haven't looked in a
code book lately how ever, Since it's not designed to teach those about
electricity, but just follow some guide lines for safety, I don't think
there is an assert about the coil being present. This is done via the
manufacturer for noise amuity. Not all may suggest to do this how ever,
if you see it packaged in a coil, bets are, you should keep it that way
or as much as possible. We have some Square-D line that will false
trigger if you remove that coil form, in the plant.

Is it an air core or ferrite? In either case, it is fairly obvious (?)
that this is something that is *meant* to be part of the assembly?
(contrast that with a pigtail that just "happens" to be coiled
up nicely for packaging)

D Yuniskis wrote:
Jamie wrote:

D Yuniskis wrote:

Also, note that there is no way a (typical) GFCI can "test
itself" to determine that it is (likely) operational. So, a
failure in the sense electronics can cripple the protection
feature in a way that is not obvious to the user (i.e., the
circuit still supplies "unprotected power").


Btw. there are Self testing GFCI's..


Really? I stand corrected (I will have to chase down the link
to see how they work). Presumably, they test the sense
electronics *while* disabling the "trip" function? (I
can't see how else they could operate as you surely wouldn't
want the circuit to open each time it tested itself : )
In which case, I guess they hope that the circuitry that
inhibits the trip never fails! :

http://www.hubbell-wiring.com/Press/PDFS/H5185.pdf

We use these extensively. Coast more, but what the hell.


What sort of cost premium? Are they required for use in
certain applications (medical, etc.)? Or, is it just
"a nice feature to have"?

Just a nice feature, its not code to have one like this and
also, code makes previsions for life saving equipment where is,
you don't install one of these devices and the receptacle is
suppose to be a coded color, if every one follows these rules ?
I don't know. As far as cost ? I'm not the one that buys them
how ever, been told they are not cheap compared to run of the mill
versions.
You must remember that anything from HUBBELL is going to have a
premium on it. For example, the guys at work tell me it's cheaper
to buy a cheap extension cord because just one HUBBELL device cost
more than the whole cord!. So I guess if you factor in the other end
, and wire, you have yourself an expensive extension cord.

And those that get a little confused with the AGFCI units
which are mostly in the modern GCFI receptacle, just not
stated. Most don't know the difference.

Those that don't have U-ground corded devices get confused when they
still see their GFCI trip just from sliding in the
plug. This only happens with the newer GFCI's that include the arc fault
detection along with the ground fault current sense.


Ah, OK. So, I assume most modern electronic loads (i.e.,
things with line switchers in them like PC's) trip these
often?

Most devices that involve switchers, which of course generates
noise, have their own common mode chokes that blocks out sufficient
noise to prevent this. Some very older switch mode supplies may cause
the AGFCI to fault how ever, at one time, and maybe you still can, you
used to be able to purchase inline filters, which were nothing but
common mode chokes.

I just love it when high powered R.F. disturbances trip those lovely
AGFCI and AFB units


RF as in *radiated* (not *conducted*)? Like someone keying
a transceiver nearby? How close do they have to be (i.e. does
this cause grief in actual *practice*)?
Oh they have to be like driving by your home and it depends on the
installation in the home it self. Service vehicles like police and
fire that do not have a clean tail drop on their transmission can cause
wide band interference and cause these arc breakers to trip.

I also like it when the installer removes what looks like excess
neutral wire that's in a coil. by by RF choke. I haven't looked in a
code book lately how ever, Since it's not designed to teach those about
electricity, but just follow some guide lines for safety, I don't think
there is an assert about the coil being present. This is done via the
manufacturer for noise amuity. Not all may suggest to do this how ever,
if you see it packaged in a coil, bets are, you should keep it that
way or as much as possible. We have some Square-D line that will false
trigger if you remove that coil form, in the plant.


Is it an air core or ferrite? In either case, it is fairly obvious (?)
that this is something that is *meant* to be part of the assembly?
(contrast that with a pigtail that just "happens" to be coiled
up nicely for packaging)
The original Arc fault breaker never had a neutral wire supplied, you
had to bond the N with the bar yourself. This didn't last long because
installers were taking short cuts and not bonding them at all. Then,
a neutral wire was supplied with each device but was just folded or
big hand coiled for boxing. It was not to long afterwards they found out
that RF was tripping these so, for quick fix, they started to ship them
with the neutral wire coiled in a tight manner so that it could be
install with most of the coil still in it's form. They had a small slip
of paper in there suggesting the installation. The last time we saw a
new box, they no longer ship any revision notes like that. SO, I guess
it's assumed that most should know to keep the wire coiled and only undo
what you need to reach the bar.
To resolve issues where these coils have been cut out and you think
there is an RFI issue. Electricians have installed large gauge chokes
inline with the neutral that belongs to the AFB device.

The last time I talked to my friend that is on the NEC code board,
that gets together annually, he stated that these devices are still
being battled out among the committee and electrical Engineers etc.. no
2 sides can come to an agreement. go figure.

I know that we had big issues using them at work on HI-POT devices
that are mounted near a water source. The very nature of the device
itself is design to hit ground when a fault occurs, which takes out the
GFCI circuit. We had to install isolation transformer service for each
one of these devices to prevent a ground current loop to develop between
the neutral and ground.

D Yuniskis wrote:
I just love it when high powered R.F. disturbances trip those lovely
AGFCI and AFB units

RF as in *radiated* (not *conducted*)? Like someone keying
a transceiver nearby? How close do they have to be (i.e. does
this cause grief in actual *practice*)?

I had one that would trip on SSB voice peaks. The antenna was a
full-wave 28 MHz loop on the balcony. Power output was about 25 watts PEP.

It was mostly my fault. I had no station ground (2nd floor apartment),
and I was feeding the loop directly with coax, which is not a recipe for
a well matched or well balanced antenna setup. I probably had RF
conducting back on the shield and getting into everything, including the
power wiring.

D Yuniskis wrote:
I just love it when high powered R.F. disturbances trip those lovely
AGFCI and AFB units

RF as in *radiated* (not *conducted*)? Like someone keying
a transceiver nearby? How close do they have to be (i.e. does
this cause grief in actual *practice*)?

I had one that would trip on SSB voice peaks. The antenna was a
full-wave 28 MHz loop on the balcony. Power output was about 25 watts PEP.

It was mostly my fault. I had no station ground (2nd floor apartment),
and I was feeding the loop directly with coax, which is not a recipe for
a well matched or well balanced antenna setup. I probably had RF
conducting back on the shield and getting into everything, including the
power wiring.