CJT wrote:
... which suggests it won't work unless/until something is drawing
current from the "hot" lead. I realize that's not much of a
restriction.


It doesn't need to work if nothing is drawing current from the hot lead.

CJT wrote:
Jeff Wisnia wrote:

Goedjn wrote:

On Wed, 29 Nov 2006 16:16:40 -0500, Jeff Wisnia
wrote:


Pop` wrote:

snipped


GFI, Ground Fault Interruptor is a misnomer. "Ground" in the
original case may have been ground, but now, because of poor
terminology, is considered the Neutral conductor. How a GFCI
operates has nothing to do with the ground. Since it senses
differences in current between the hot/neutral conductors, any
third wire earth ground is irrelevant to its opeartion. Hot amps =
Neutral amps, all OK. Not equal, it trips. It's literally that
simple.

Pop`



And, don't forget that the more recent GFCI's will detect a leakage
path between the neutral and ground as well, and thus disconnect
power when there's a neutral to ground short.

Jeff




Ok, I thought I knew how GFCI outlets worked, and now I find out that
I didn't know how the test button worked. Fine, I'm ok with
that, but this doesn't make any sense. It seems as if
a nuetral-ground leak should look exactly like a hot-ground leak,
except probably smaller, as there's less resistance downstream
of the correct current path.

How would you tell the difference even if you wanted to?

--Goedjn



I didn't SAY that they tell the "difference". Since their only "output
means" is to open the circuit between the supply and load side of the
breaker for either kind of fault, hot to ground leakage or neutral to
ground shorts.

They will detect and "pop" if you make a connection between their
neutral output and ground, even with nothing at all connected to their
hot output.

Before you worry too much about how they can sense a connection
between two leads which should be at the same potential (neutral and
ground) if there isn't any current flowing in either of them, I'll
tell you that there will be, because the GFCI contains a current
transformer which adds a small in-phase voltage to both the hot and
neutral output leads.


... which suggests it won't work unless/until something is drawing
current from the "hot" lead. I realize that's not much of a
restriction.

Nope, there's a 120 volt "primary" on that "current transformer" which
is connected across the incoming line. The incoming hot and neutral
leads to the GFCI are "secondaries" on that transformer, and a small
amount of in phase voltage gets "added" in series to both of them. Then,
those leads continue through the normal differential current sensing
transformer and on to the "load" side of the GFCI.

My calling it a "current transformer" may not be exactly correct, but
they are transformers having one winding with lots of turns of fine wire
and two winding of wire heavy enough to carry the rated current of the
GFCI. I believe both the "transformers" in a GFCI are wound on toroidal
cores, and that the "heavy" leads may wind around the cores only one
turn or so.

With enough Googling you can probably find a simplified schematic of
what's inside a GFCI, and a picture is worth a thousand words when it
comes to understanding the current flows involved.

Jeff

--
Jeffry Wisnia
(W1BSV + Brass Rat '57 EE)
The speed of light is 1.8*10^12 furlongs per fortnight.





That voltage on the neutral lead will cause a small current flow if
the neutral gets connected to ground. The normal differential current
sensing portion of the GFCI responds to the current flowing in the
neutral which has not come from the hot output and "pops" the GFCI.

Trust me it works... Or test it yourself with a neutral to ground short.

Jeff

Goedjn wrote:

On Thu, 30 Nov 2006 00:14:03 -0500, Jeff Wisnia
wrote:


Goedjn wrote:

On Wed, 29 Nov 2006 16:16:40 -0500, Jeff Wisnia
wrote:



Pop` wrote:

snipped

GFI, Ground Fault Interruptor is a misnomer. "Ground" in the original case
may have been ground, but now, because of poor terminology, is considered
the Neutral conductor. How a GFCI operates has nothing to do with the
ground. Since it senses differences in current between the hot/neutral
conductors, any third wire earth ground is irrelevant to its opeartion. Hot
amps = Neutral amps, all OK. Not equal, it trips. It's literally that
simple.

Pop`



And, don't forget that the more recent GFCI's will detect a leakage path
between the neutral and ground as well, and thus disconnect power when
there's a neutral to ground short.

Jeff


Ok, I thought I knew how GFCI outlets worked, and now I find out
that I didn't know how the test button worked. Fine, I'm ok with
that, but this doesn't make any sense. It seems as if
a nuetral-ground leak should look exactly like a hot-ground
leak, except probably smaller, as there's less resistance downstream
of the correct current path.

How would you tell the difference even if you wanted to?

--Goedjn

I didn't SAY that they tell the "difference". Since their only "output
means" is to open the circuit between the supply and load side of the
breaker for either kind of fault, hot to ground leakage or neutral to
ground shorts.

They will detect and "pop" if you make a connection between their
neutral output and ground, even with nothing at all connected to their
hot output.

Before you worry too much about how they can sense a connection between
two leads which should be at the same potential (neutral and ground) if
there isn't any current flowing in either of them, I'll tell you that
there will be, because the GFCI contains a current transformer which
adds a small in-phase voltage to both the hot and neutral output leads.

That voltage on the neutral lead will cause a small current flow if the
neutral gets connected to ground. The normal differential current
sensing portion of the GFCI responds to the current flowing in the
neutral which has not come from the hot output and "pops" the GFCI.

Trust me it works... Or test it yourself with a neutral to ground short.

Jeff


What was confusing me was the implication that there's an
older type of GFCI that will trip on a hot/ground short,
but not on a nuetral/ground short. Was I inferring more
from "more recent GFCIs" than was intended?



That's what I've been led to believe, but I can't swear to it.

GFCIs have been around for well over twenty years. Our home is 21 years
old and came from the builder with one GFCI breaker in the panel and a
couple of GFCI outlets too.

Jeff

--
Jeffry Wisnia
(W1BSV + Brass Rat '57 EE)
The speed of light is 1.8*10^12 furlongs per fortnight.

Terry wrote:

CJT wrote:

... which suggests it won't work unless/until something is drawing
current from the "hot" lead. I realize that's not much of a
restriction.



It doesn't need to work if nothing is drawing current from the hot lead.


BUT IT DOES!

I finally found Sam Goldwasser's page which is pretty much the bible
about GFCI's. It has the diagrams I'd been trying to find again.

http://www.codecheck.com/gfci_principal.htm

I found the last paragraph explaining why kitchen toasters don't have
grounded cords on them pretty logical.

Read it and learn...

Happy Holidays,

Jeff

--
Jeffry Wisnia
(W1BSV + Brass Rat '57 EE)
The speed of light is 1.8*10^12 furlongs per fortnight.

Jeff Wisnia wrote:
Terry wrote:

CJT wrote:

... which suggests it won't work unless/until something is drawing
current from the "hot" lead. I realize that's not much of a
restriction.



It doesn't need to work if nothing is drawing current from the hot lead.


BUT IT DOES!

I finally found Sam Goldwasser's page which is pretty much the bible
about GFCI's. It has the diagrams I'd been trying to find again.

http://www.codecheck.com/gfci_principal.htm

I found the last paragraph explaining why kitchen toasters don't have
grounded cords on them pretty logical.

Read it and learn...

Useful information.

I got a chuckle from the diagram that says fault current (bad)

It made me think of........Fire bad. You would have to be a Saturday
Night Live fan to get it.

Jeff Wisnia wrote:

CJT wrote:

Jeff Wisnia wrote:

Goedjn wrote:

On Wed, 29 Nov 2006 16:16:40 -0500, Jeff Wisnia
wrote:


Pop` wrote:

snipped


GFI, Ground Fault Interruptor is a misnomer. "Ground" in the
original case may have been ground, but now, because of poor
terminology, is considered the Neutral conductor. How a GFCI
operates has nothing to do with the ground. Since it senses
differences in current between the hot/neutral conductors, any
third wire earth ground is irrelevant to its opeartion. Hot amps
= Neutral amps, all OK. Not equal, it trips. It's literally that
simple.

Pop`



And, don't forget that the more recent GFCI's will detect a leakage
path between the neutral and ground as well, and thus disconnect
power when there's a neutral to ground short.

Jeff





Ok, I thought I knew how GFCI outlets worked, and now I find out
that I didn't know how the test button worked. Fine, I'm ok with
that, but this doesn't make any sense. It seems as if
a nuetral-ground leak should look exactly like a hot-ground leak,
except probably smaller, as there's less resistance downstream
of the correct current path.

How would you tell the difference even if you wanted to?

--Goedjn




I didn't SAY that they tell the "difference". Since their only
"output means" is to open the circuit between the supply and load
side of the breaker for either kind of fault, hot to ground leakage
or neutral to ground shorts.

They will detect and "pop" if you make a connection between their
neutral output and ground, even with nothing at all connected to
their hot output.

Before you worry too much about how they can sense a connection
between two leads which should be at the same potential (neutral and
ground) if there isn't any current flowing in either of them, I'll
tell you that there will be, because the GFCI contains a current
transformer which adds a small in-phase voltage to both the hot and
neutral output leads.



... which suggests it won't work unless/until something is drawing
current from the "hot" lead. I realize that's not much of a
restriction.


Nope, there's a 120 volt "primary" on that "current transformer" which
is connected across the incoming line. The incoming hot and neutral
leads to the GFCI are "secondaries" on that transformer, and a small
amount of in phase voltage gets "added" in series to both of them. Then,
those leads continue through the normal differential current sensing
transformer and on to the "load" side of the GFCI.

My calling it a "current transformer" may not be exactly correct, but
they are transformers having one winding with lots of turns of fine wire
and two winding of wire heavy enough to carry the rated current of the
GFCI.

Now I understand. It was the terminology that threw me off. "Current
transformer" means something a bit different to me.

Regardless, that seems like an awful lot of technology to throw at a
problem that doesn't seem (to me) like much of a problem. Since the
ground and neutral are tied together upstream, why is it a problem if
they're also tied together downstream? I.e., what am I missing in this
picture? Won't normal GFCI functionality catch any such case that's a
significant hazard?

I believe both the "transformers" in a GFCI are wound on toroidal
cores, and that the "heavy" leads may wind around the cores only one
turn or so.

With enough Googling you can probably find a simplified schematic of
what's inside a GFCI, and a picture is worth a thousand words when it
comes to understanding the current flows involved.

Jeff



--
The e-mail address in our reply-to line is reversed in an attempt to
minimize spam. Our true address is of the form .

Jeff Wisnia wrote:

Goedjn wrote:

On Thu, 30 Nov 2006 00:14:03 -0500, Jeff Wisnia
wrote:


Goedjn wrote:

On Wed, 29 Nov 2006 16:16:40 -0500, Jeff Wisnia
wrote:



Pop` wrote:

snipped

GFI, Ground Fault Interruptor is a misnomer. "Ground" in the
original case may have been ground, but now, because of poor
terminology, is considered the Neutral conductor. How a GFCI
operates has nothing to do with the ground. Since it senses
differences in current between the hot/neutral conductors, any
third wire earth ground is irrelevant to its opeartion. Hot amps
= Neutral amps, all OK. Not equal, it trips. It's literally that
simple.

Pop`



And, don't forget that the more recent GFCI's will detect a leakage
path between the neutral and ground as well, and thus disconnect
power when there's a neutral to ground short.

Jeff



Ok, I thought I knew how GFCI outlets worked, and now I find out
that I didn't know how the test button worked. Fine, I'm ok with
that, but this doesn't make any sense. It seems as if
a nuetral-ground leak should look exactly like a hot-ground leak,
except probably smaller, as there's less resistance downstream
of the correct current path.

How would you tell the difference even if you wanted to?

--Goedjn


I didn't SAY that they tell the "difference". Since their only
"output means" is to open the circuit between the supply and load
side of the breaker for either kind of fault, hot to ground leakage
or neutral to ground shorts.

They will detect and "pop" if you make a connection between their
neutral output and ground, even with nothing at all connected to
their hot output.

Before you worry too much about how they can sense a connection
between two leads which should be at the same potential (neutral and
ground) if there isn't any current flowing in either of them, I'll
tell you that there will be, because the GFCI contains a current
transformer which adds a small in-phase voltage to both the hot and
neutral output leads.

That voltage on the neutral lead will cause a small current flow if
the neutral gets connected to ground. The normal differential current
sensing portion of the GFCI responds to the current flowing in the
neutral which has not come from the hot output and "pops" the GFCI.

Trust me it works... Or test it yourself with a neutral to ground short.

Jeff



What was confusing me was the implication that there's an
older type of GFCI that will trip on a hot/ground short, but not on a
nuetral/ground short. Was I inferring more
from "more recent GFCIs" than was intended?



That's what I've been led to believe, but I can't swear to it.

GFCIs have been around for well over twenty years. Our home is 21 years
old and came from the builder with one GFCI breaker in the panel and a
couple of GFCI outlets too.

Jeff

Ours was built in 1980 and contained a GFCI outlet when it was new.

--
The e-mail address in our reply-to line is reversed in an attempt to
minimize spam. Our true address is of the form .

In article ,
says...
Jeff Wisnia wrote:

CJT wrote:

Jeff Wisnia wrote:

Goedjn wrote:

On Wed, 29 Nov 2006 16:16:40 -0500, Jeff Wisnia
wrote:


Pop` wrote:

snipped


GFI, Ground Fault Interruptor is a misnomer. "Ground" in the
original case may have been ground, but now, because of poor
terminology, is considered the Neutral conductor. How a GFCI
operates has nothing to do with the ground. Since it senses
differences in current between the hot/neutral conductors, any
third wire earth ground is irrelevant to its opeartion. Hot amps
= Neutral amps, all OK. Not equal, it trips. It's literally that
simple.

Pop`



And, don't forget that the more recent GFCI's will detect a leakage
path between the neutral and ground as well, and thus disconnect
power when there's a neutral to ground short.

Jeff





Ok, I thought I knew how GFCI outlets worked, and now I find out
that I didn't know how the test button worked. Fine, I'm ok with
that, but this doesn't make any sense. It seems as if
a nuetral-ground leak should look exactly like a hot-ground leak,
except probably smaller, as there's less resistance downstream
of the correct current path.

How would you tell the difference even if you wanted to?

--Goedjn




I didn't SAY that they tell the "difference". Since their only
"output means" is to open the circuit between the supply and load
side of the breaker for either kind of fault, hot to ground leakage
or neutral to ground shorts.

They will detect and "pop" if you make a connection between their
neutral output and ground, even with nothing at all connected to
their hot output.

Before you worry too much about how they can sense a connection
between two leads which should be at the same potential (neutral and
ground) if there isn't any current flowing in either of them, I'll
tell you that there will be, because the GFCI contains a current
transformer which adds a small in-phase voltage to both the hot and
neutral output leads.



... which suggests it won't work unless/until something is drawing
current from the "hot" lead. I realize that's not much of a
restriction.


Nope, there's a 120 volt "primary" on that "current transformer" which
is connected across the incoming line. The incoming hot and neutral
leads to the GFCI are "secondaries" on that transformer, and a small
amount of in phase voltage gets "added" in series to both of them. Then,
those leads continue through the normal differential current sensing
transformer and on to the "load" side of the GFCI.

My calling it a "current transformer" may not be exactly correct, but
they are transformers having one winding with lots of turns of fine wire
and two winding of wire heavy enough to carry the rated current of the
GFCI.

Now I understand. It was the terminology that threw me off. "Current
transformer" means something a bit different to me.

Ok, what does it mean to you? GFCI indeed do use current
transformers to detect the imbalance in current between the hot an
neutral.

Regardless, that seems like an awful lot of technology to throw at a
problem that doesn't seem (to me) like much of a problem.

A fault to ground isn't a big deal to you? boggle

Since the
ground and neutral are tied together upstream, why is it a problem if
they're also tied together downstream?

Wow! Perhaps because a neutral is designed to carry CURRENT, and a
ground is *NOT*. THink about faults! The ground is there for
safety!

I.e., what am I missing in this picture?

Faults.

Won't normal GFCI functionality catch any such case that's a
significant hazard?

A parachute might catch you too, but it's a good idea to never have
rely on one.

--
Keith

krw wrote:

In article ,
says...

Jeff Wisnia wrote:


CJT wrote:


Jeff Wisnia wrote:


Goedjn wrote:


On Wed, 29 Nov 2006 16:16:40 -0500, Jeff Wisnia
wrote:



Pop` wrote:

snipped

GFI, Ground Fault Interruptor is a misnomer. "Ground" in the
original case may have been ground, but now, because of poor
terminology, is considered the Neutral conductor. How a GFCI
operates has nothing to do with the ground. Since it senses
differences in current between the hot/neutral conductors, any
third wire earth ground is irrelevant to its opeartion. Hot amps
= Neutral amps, all OK. Not equal, it trips. It's literally that
simple.

Pop`



And, don't forget that the more recent GFCI's will detect a leakage
path between the neutral and ground as well, and thus disconnect
power when there's a neutral to ground short.

Jeff





Ok, I thought I knew how GFCI outlets worked, and now I find out
that I didn't know how the test button worked. Fine, I'm ok with
that, but this doesn't make any sense. It seems as if
a nuetral-ground leak should look exactly like a hot-ground leak,
except probably smaller, as there's less resistance downstream
of the correct current path.

How would you tell the difference even if you wanted to?

--Goedjn




I didn't SAY that they tell the "difference". Since their only
"output means" is to open the circuit between the supply and load
side of the breaker for either kind of fault, hot to ground leakage
or neutral to ground shorts.

They will detect and "pop" if you make a connection between their
neutral output and ground, even with nothing at all connected to
their hot output.

Before you worry too much about how they can sense a connection
between two leads which should be at the same potential (neutral and
ground) if there isn't any current flowing in either of them, I'll
tell you that there will be, because the GFCI contains a current
transformer which adds a small in-phase voltage to both the hot and
neutral output leads.



... which suggests it won't work unless/until something is drawing
current from the "hot" lead. I realize that's not much of a
restriction.


Nope, there's a 120 volt "primary" on that "current transformer" which
is connected across the incoming line. The incoming hot and neutral
leads to the GFCI are "secondaries" on that transformer, and a small
amount of in phase voltage gets "added" in series to both of them. Then,
those leads continue through the normal differential current sensing
transformer and on to the "load" side of the GFCI.

My calling it a "current transformer" may not be exactly correct, but
they are transformers having one winding with lots of turns of fine wire
and two winding of wire heavy enough to carry the rated current of the
GFCI.

Now I understand. It was the terminology that threw me off. "Current
transformer" means something a bit different to me.


Ok, what does it mean to you? GFCI indeed do use current
transformers to detect the imbalance in current between the hot an
neutral.

But that's not the section of the GFCI we were discussing. In what
sense is it a "current transformer" if it has a primary connected
between hot and neutral?

Regardless, that seems like an awful lot of technology to throw at a
problem that doesn't seem (to me) like much of a problem.


A fault to ground isn't a big deal to you? boggle

I fail to see how a fault between ground and neutral (of the sort we
were discussing) downstream of a GFCI, without some additional fault,
will get you electrocuted.


Since the

ground and neutral are tied together upstream, why is it a problem if
they're also tied together downstream?


Wow! Perhaps because a neutral is designed to carry CURRENT, and a
ground is *NOT*. THink about faults! The ground is there for
safety!

Fair enough (reserve the ground to its safety role). But you don't,
e.g., protect against faults that circumvent the GFCI. At some point
the addition of safety devices becomes overdone. How will a
ground-neutral fault downstream of a GFCI, without some other additional
fault, get you electrocuted?

BTW, if a ground is incapable of carrying current (as you seem to
imply), it's not much use as protection.


I.e., what am I missing in this picture?


Faults.

No, I'm well aware of the possibility of faults.


Won't normal GFCI functionality catch any such case that's a
significant hazard?


A parachute might catch you too, but it's a good idea to never have
rely on one.

There are already multiple levels of protection. The question is
when one stops adding more.

--
The e-mail address in our reply-to line is reversed in an attempt to
minimize spam. Our true address is of the form .

In article , CJT wrote:

I fail to see how a fault between ground and neutral (of the sort we
were discussing) downstream of a GFCI, without some additional fault,
will get you electrocuted.

Because:
a) the ground conductor is attached to the metal frame of any equipment that
has one;
b) the neutral conductor carries current;
c) tying the ground and neutral together, downstream of the main panel, causes
the metal frame of any equipment having one to be electrically continuous with
the neutral;
and therefore
d) a parallel path to ground exists, for the current flowing in the neutral,
through the body of any person who happens to be touching said metal frame.

Fair enough (reserve the ground to its safety role). But you don't,
e.g., protect against faults that circumvent the GFCI. At some point
the addition of safety devices becomes overdone. How will a
ground-neutral fault downstream of a GFCI, without some other additional
fault, get you electrocuted?

Explained above.

BTW, if a ground is incapable of carrying current (as you seem to
imply), it's not much use as protection.

Of course it's capable of it. The point is that in normal operation, it's not
supposed to.

--
Regards,
Doug Miller (alphageek at milmac dot com)

It's time to throw all their damned tea in the harbor again.

Doug Miller wrote:
In article , CJT wrote:


I fail to see how a fault between ground and neutral (of the sort we
were discussing) downstream of a GFCI, without some additional fault,
will get you electrocuted.


Because:
a) the ground conductor is attached to the metal frame of any equipment that
has one;
b) the neutral conductor carries current;
c) tying the ground and neutral together, downstream of the main panel, causes
the metal frame of any equipment having one to be electrically continuous with
the neutral;
and therefore
d) a parallel path to ground exists, for the current flowing in the neutral,
through the body of any person who happens to be touching said metal frame.

But neither neutral nor ground should be more than a couple of volts
above zero potential, barring an additional fault. I can see getting
a tingle, but electrocuted?



Fair enough (reserve the ground to its safety role). But you don't,
e.g., protect against faults that circumvent the GFCI. At some point
the addition of safety devices becomes overdone. How will a
ground-neutral fault downstream of a GFCI, without some other additional
fault, get you electrocuted?


Explained above.


BTW, if a ground is incapable of carrying current (as you seem to
imply), it's not much use as protection.


Of course it's capable of it. The point is that in normal operation, it's not
supposed to.



--
The e-mail address in our reply-to line is reversed in an attempt to
minimize spam. Our true address is of the form .

In article , CJT wrote:
But neither neutral nor ground should be more than a couple of volts
above zero potential, barring an additional fault. I can see getting
a tingle, but electrocuted?

If the current passes across the heart (e.g. hand to hand, or hand to opposite
foot), as little as twenty milliamperes can be fatal.

--
Regards,
Doug Miller (alphageek at milmac dot com)

It's time to throw all their damned tea in the harbor again.

Doug Miller wrote:

In article , CJT wrote:

But neither neutral nor ground should be more than a couple of volts
above zero potential, barring an additional fault. I can see getting
a tingle, but electrocuted?


If the current passes across the heart (e.g. hand to hand, or hand to opposite
foot), as little as twenty milliamperes can be fatal.


better be careful with those AAA batteries

--
The e-mail address in our reply-to line is reversed in an attempt to
minimize spam. Our true address is of the form .

CJT wrote:

Doug Miller wrote:

In article , CJT
wrote:

But neither neutral nor ground should be more than a couple of volts
above zero potential, barring an additional fault. I can see getting
a tingle, but electrocuted?



If the current passes across the heart (e.g. hand to hand, or hand to
opposite foot), as little as twenty milliamperes can be fatal.


better be careful with those AAA batteries


You know, I have long pondered the same question, since "circuit wise"
it's hard to see why the neutral wire wouldn't serve as a reasonable
"ground" IF you neglect wiring resistance and assume that all wire
terminations, once made, will remain perfect and continuous forever.

But, we know that's not always the case, and while I agree that a few
volts created by an IR drop in the return lead won't hurt you unless it
somehow "gets under your skin", if you've never stuck your tongue across
the terminals of a 9 volt "transistor radio battery", you'd be shocked,
(Even more than Captain Renault was.) to "see how that tastes."

But, consider what maybe 3 to 5 volts of neutral voltage drop with
several amps of current source driving it might do in terms of heating
up some thin strip of metal, like say a piece of Xmas tree tinsel.
(Izzat stuff still metal? It was when I was a kid.) That could raise its
temperature enough to start a fire.

So, all things considered, especially IPIO*, I think I must agree that
the addition of safety grounding to building wiring, which occurred
sometime during my life so far, was probably a pretty good idea, as are
GFCIs.

Jeff

* IPIO: the innate perversity of inanimate objects

--
Jeffry Wisnia
(W1BSV + Brass Rat '57 EE)
The speed of light is 1.8*10^12 furlongs per fortnight.

"Jeff Wisnia" wrote in message
et...
Terry wrote:

CJT wrote:

... which suggests it won't work unless/until something is drawing
current from the "hot" lead. I realize that's not much of a
restriction.



It doesn't need to work if nothing is drawing current from the hot lead.


BUT IT DOES!

I finally found Sam Goldwasser's page which is pretty much the bible
about GFCI's. It has the diagrams I'd been trying to find again.

http://www.codecheck.com/gfci_principal.htm

I found the last paragraph explaining why kitchen toasters don't have
grounded cords on them pretty logical.

Read it and learn...

Happy Holidays,

Jeff

--
Jeffry Wisnia

http://www.national.com/ds/LM/LM1851.pdf
(W1BSV + Brass Rat '57 EE)
The speed of light is 1.8*10^12 furlongs per fortnight.

In article ,
says...
krw wrote:

In article ,
says...

Jeff Wisnia wrote:


CJT wrote:


Jeff Wisnia wrote:


Goedjn wrote:


On Wed, 29 Nov 2006 16:16:40 -0500, Jeff Wisnia
wrote:



Pop` wrote:

snipped

GFI, Ground Fault Interruptor is a misnomer. "Ground" in the
original case may have been ground, but now, because of poor
terminology, is considered the Neutral conductor. How a GFCI
operates has nothing to do with the ground. Since it senses
differences in current between the hot/neutral conductors, any
third wire earth ground is irrelevant to its opeartion. Hot amps
= Neutral amps, all OK. Not equal, it trips. It's literally that
simple.

Pop`



And, don't forget that the more recent GFCI's will detect a leakage
path between the neutral and ground as well, and thus disconnect
power when there's a neutral to ground short.

Jeff





Ok, I thought I knew how GFCI outlets worked, and now I find out
that I didn't know how the test button worked. Fine, I'm ok with
that, but this doesn't make any sense. It seems as if
a nuetral-ground leak should look exactly like a hot-ground leak,
except probably smaller, as there's less resistance downstream
of the correct current path.

How would you tell the difference even if you wanted to?

--Goedjn




I didn't SAY that they tell the "difference". Since their only
"output means" is to open the circuit between the supply and load
side of the breaker for either kind of fault, hot to ground leakage
or neutral to ground shorts.

They will detect and "pop" if you make a connection between their
neutral output and ground, even with nothing at all connected to
their hot output.

Before you worry too much about how they can sense a connection
between two leads which should be at the same potential (neutral and
ground) if there isn't any current flowing in either of them, I'll
tell you that there will be, because the GFCI contains a current
transformer which adds a small in-phase voltage to both the hot and
neutral output leads.



... which suggests it won't work unless/until something is drawing
current from the "hot" lead. I realize that's not much of a
restriction.


Nope, there's a 120 volt "primary" on that "current transformer" which
is connected across the incoming line. The incoming hot and neutral
leads to the GFCI are "secondaries" on that transformer, and a small
amount of in phase voltage gets "added" in series to both of them. Then,
those leads continue through the normal differential current sensing
transformer and on to the "load" side of the GFCI.

My calling it a "current transformer" may not be exactly correct, but
they are transformers having one winding with lots of turns of fine wire
and two winding of wire heavy enough to carry the rated current of the
GFCI.

Now I understand. It was the terminology that threw me off. "Current
transformer" means something a bit different to me.


Ok, what does it mean to you? GFCI indeed do use current
transformers to detect the imbalance in current between the hot an
neutral.

But that's not the section of the GFCI we were discussing. In what
sense is it a "current transformer" if it has a primary connected
between hot and neutral?

Primary connected between hot and neutral? What _are_ you talking
about?

The hot and neutral have separate "windings". The current imbalance
is sensed with a third "winding". WHen the current in each of the
hot and neutral is the same the magnetic fields cancel, thus
nothing on the sense winding. If there is a current imbalance
there is a net magnetic field and is sensed. It is the difference
in current that's sensed, thus a current transformer.

Regardless, that seems like an awful lot of technology to throw at a
problem that doesn't seem (to me) like much of a problem.


A fault to ground isn't a big deal to you? boggle

I fail to see how a fault between ground and neutral (of the sort we
were discussing) downstream of a GFCI, without some additional fault,
will get you electrocuted.

If there is a neutral fault you're now in the circuit. This isn't
a healthy idea.

Since the

ground and neutral are tied together upstream, why is it a problem if
they're also tied together downstream?


Wow! Perhaps because a neutral is designed to carry CURRENT, and a
ground is *NOT*. THink about faults! The ground is there for
safety!

Fair enough (reserve the ground to its safety role). But you don't,
e.g., protect against faults that circumvent the GFCI.

What faults would those be?

At some point
the addition of safety devices becomes overdone. How will a
ground-neutral fault downstream of a GFCI, without some other additional
fault, get you electrocuted?

Likely not. Do you want to take that chance though? Please leave
my wiring alone.

BTW, if a ground is incapable of carrying current (as you seem to
imply), it's not much use as protection.

I didn't say "incapable", I said *DOESN'T*, there is a difference.

I.e., what am I missing in this picture?


Faults.

No, I'm well aware of the possibility of faults.

Apparently not.

Won't normal GFCI functionality catch any such case that's a
significant hazard?


A parachute might catch you too, but it's a good idea to never have
rely on one.

There are already multiple levels of protection. The question is
when one stops adding more.

When one is happy with the level of protection, after all
applicable safety codes have been met.

--
Keith

krw wrote:

In article ,
says...

krw wrote:


In article ,
says...


Jeff Wisnia wrote:



CJT wrote:



Jeff Wisnia wrote:



Goedjn wrote:



On Wed, 29 Nov 2006 16:16:40 -0500, Jeff Wisnia
wrote:




Pop` wrote:

snipped

GFI, Ground Fault Interruptor is a misnomer. "Ground" in the
original case may have been ground, but now, because of poor
terminology, is considered the Neutral conductor. How a GFCI
operates has nothing to do with the ground. Since it senses
differences in current between the hot/neutral conductors, any
third wire earth ground is irrelevant to its opeartion. Hot amps
= Neutral amps, all OK. Not equal, it trips. It's literally that
simple.

Pop`



And, don't forget that the more recent GFCI's will detect a leakage
path between the neutral and ground as well, and thus disconnect
power when there's a neutral to ground short.

Jeff





Ok, I thought I knew how GFCI outlets worked, and now I find out
that I didn't know how the test button worked. Fine, I'm ok with
that, but this doesn't make any sense. It seems as if
a nuetral-ground leak should look exactly like a hot-ground leak,
except probably smaller, as there's less resistance downstream
of the correct current path.

How would you tell the difference even if you wanted to?

--Goedjn




I didn't SAY that they tell the "difference". Since their only
"output means" is to open the circuit between the supply and load
side of the breaker for either kind of fault, hot to ground leakage
or neutral to ground shorts.

They will detect and "pop" if you make a connection between their
neutral output and ground, even with nothing at all connected to
their hot output.

Before you worry too much about how they can sense a connection
between two leads which should be at the same potential (neutral and
ground) if there isn't any current flowing in either of them, I'll
tell you that there will be, because the GFCI contains a current
transformer which adds a small in-phase voltage to both the hot and
neutral output leads.



... which suggests it won't work unless/until something is drawing
current from the "hot" lead. I realize that's not much of a
restriction.


Nope, there's a 120 volt "primary" on that "current transformer" which
is connected across the incoming line.

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ ^^^^^^^^^^^^^^^^^^^HERE!



The incoming hot and neutral
leads to the GFCI are "secondaries" on that transformer, and a small
amount of in phase voltage gets "added" in series to both of them. Then,
those leads continue through the normal differential current sensing
transformer and on to the "load" side of the GFCI.

My calling it a "current transformer" may not be exactly correct, but
they are transformers having one winding with lots of turns of fine wire
and two winding of wire heavy enough to carry the rated current of the
GFCI.

Now I understand. It was the terminology that threw me off. "Current
transformer" means something a bit different to me.


Ok, what does it mean to you? GFCI indeed do use current
transformers to detect the imbalance in current between the hot an
neutral.


But that's not the section of the GFCI we were discussing. In what
sense is it a "current transformer" if it has a primary connected
between hot and neutral?


Primary connected between hot and neutral? What _are_ you talking
about?

The portion of the thread identified above.


The hot and neutral have separate "windings". The current imbalance
is sensed with a third "winding". WHen the current in each of the
hot and neutral is the same the magnetic fields cancel, thus
nothing on the sense winding. If there is a current imbalance
there is a net magnetic field and is sensed. It is the difference
in current that's sensed, thus a current transformer.


That's a different part of the device, like I said.


Regardless, that seems like an awful lot of technology to throw at a
problem that doesn't seem (to me) like much of a problem.


A fault to ground isn't a big deal to you? boggle

I fail to see how a fault between ground and neutral (of the sort we
were discussing) downstream of a GFCI, without some additional fault,
will get you electrocuted.


If there is a neutral fault you're now in the circuit. This isn't
a healthy idea.


But is it life threatening? Unlikely.

Since the


ground and neutral are tied together upstream, why is it a problem if
they're also tied together downstream?


Wow! Perhaps because a neutral is designed to carry CURRENT, and a
ground is *NOT*. THink about faults! The ground is there for
safety!

Fair enough (reserve the ground to its safety role). But you don't,
e.g., protect against faults that circumvent the GFCI.


What faults would those be?

For instance, a short across the GFCI that effectively takes it out
of the circuit.


At some point
the addition of safety devices becomes overdone. How will a
ground-neutral fault downstream of a GFCI, without some other additional
fault, get you electrocuted?


Likely not. Do you want to take that chance though? Please leave
my wiring alone.

I don't like people taking chances with my life by talking on their
cellphones while driving, either, but that doesn't necessarily mean
there should be interlocks on their car to prevent it.



BTW, if a ground is incapable of carrying current (as you seem to
imply), it's not much use as protection.


I didn't say "incapable", I said *DOESN'T*, there is a difference.

You said the ground was not "designed to carry current." Perhaps I
read that too literally.



I.e., what am I missing in this picture?


Faults.


No, I'm well aware of the possibility of faults.


Apparently not.

Pfft.


Won't normal GFCI functionality catch any such case that's a
significant hazard?


A parachute might catch you too, but it's a good idea to never have
rely on one.


There are already multiple levels of protection. The question is
when one stops adding more.


When one is happy with the level of protection, after all
applicable safety codes have been met.


Whatever.

--
The e-mail address in our reply-to line is reversed in an attempt to
minimize spam. Our true address is of the form .

In article ,
says...
krw wrote:

In article ,
says...

krw wrote:


In article ,
says...


Jeff Wisnia wrote:



CJT wrote:



Jeff Wisnia wrote:



Goedjn wrote:



On Wed, 29 Nov 2006 16:16:40 -0500, Jeff Wisnia
wrote:




Pop` wrote:

snipped

GFI, Ground Fault Interruptor is a misnomer. "Ground" in the
original case may have been ground, but now, because of poor
terminology, is considered the Neutral conductor. How a GFCI
operates has nothing to do with the ground. Since it senses
differences in current between the hot/neutral conductors, any
third wire earth ground is irrelevant to its opeartion. Hot amps
= Neutral amps, all OK. Not equal, it trips. It's literally that
simple.

Pop`



And, don't forget that the more recent GFCI's will detect a leakage
path between the neutral and ground as well, and thus disconnect
power when there's a neutral to ground short.

Jeff





Ok, I thought I knew how GFCI outlets worked, and now I find out
that I didn't know how the test button worked. Fine, I'm ok with
that, but this doesn't make any sense. It seems as if
a nuetral-ground leak should look exactly like a hot-ground leak,
except probably smaller, as there's less resistance downstream
of the correct current path.

How would you tell the difference even if you wanted to?

--Goedjn




I didn't SAY that they tell the "difference". Since their only
"output means" is to open the circuit between the supply and load
side of the breaker for either kind of fault, hot to ground leakage
or neutral to ground shorts.

They will detect and "pop" if you make a connection between their
neutral output and ground, even with nothing at all connected to
their hot output.

Before you worry too much about how they can sense a connection
between two leads which should be at the same potential (neutral and
ground) if there isn't any current flowing in either of them, I'll
tell you that there will be, because the GFCI contains a current
transformer which adds a small in-phase voltage to both the hot and
neutral output leads.



... which suggests it won't work unless/until something is drawing
current from the "hot" lead. I realize that's not much of a
restriction.


Nope, there's a 120 volt "primary" on that "current transformer" which
is connected across the incoming line.

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ ^^^^^^^^^^^^^^^^^^^HERE!



The incoming hot and neutral
leads to the GFCI are "secondaries" on that transformer, and a small
amount of in phase voltage gets "added" in series to both of them. Then,
those leads continue through the normal differential current sensing
transformer and on to the "load" side of the GFCI.

My calling it a "current transformer" may not be exactly correct, but
they are transformers having one winding with lots of turns of fine wire
and two winding of wire heavy enough to carry the rated current of the
GFCI.

Now I understand. It was the terminology that threw me off. "Current
transformer" means something a bit different to me.


Ok, what does it mean to you? GFCI indeed do use current
transformers to detect the imbalance in current between the hot an
neutral.


But that's not the section of the GFCI we were discussing. In what
sense is it a "current transformer" if it has a primary connected
between hot and neutral?


Primary connected between hot and neutral? What _are_ you talking
about?

The portion of the thread identified above.

Your writing isn't clear. The current transformer is a current
transformer, no more, no less. "Primary" of what?

The hot and neutral have separate "windings". The current imbalance
is sensed with a third "winding". WHen the current in each of the
hot and neutral is the same the magnetic fields cancel, thus
nothing on the sense winding. If there is a current imbalance
there is a net magnetic field and is sensed. It is the difference
in current that's sensed, thus a current transformer.


That's a different part of the device, like I said.

That's pretty much the *entire* device.


Regardless, that seems like an awful lot of technology to throw at a
problem that doesn't seem (to me) like much of a problem.


A fault to ground isn't a big deal to you? boggle

I fail to see how a fault between ground and neutral (of the sort we
were discussing) downstream of a GFCI, without some additional fault,
will get you electrocuted.


If there is a neutral fault you're now in the circuit. This isn't
a healthy idea.


But is it life threatening? Unlikely.

120V on the case isn't threatening? boggle

Since the


ground and neutral are tied together upstream, why is it a problem if
they're also tied together downstream?


Wow! Perhaps because a neutral is designed to carry CURRENT, and a
ground is *NOT*. THink about faults! The ground is there for
safety!

Fair enough (reserve the ground to its safety role). But you don't,
e.g., protect against faults that circumvent the GFCI.


What faults would those be?

For instance, a short across the GFCI that effectively takes it out
of the circuit.

A short across the breaker takes it out of the circuit too. So?

At some point
the addition of safety devices becomes overdone. How will a
ground-neutral fault downstream of a GFCI, without some other additional
fault, get you electrocuted?


Likely not. Do you want to take that chance though? Please leave
my wiring alone.

I don't like people taking chances with my life by talking on their
cellphones while driving, either, but that doesn't necessarily mean
there should be interlocks on their car to prevent it.

There have been enough people killed that GFCIs were written into
the code for places where they would have saved lives. It's been
said that the NEC is written in blood.


BTW, if a ground is incapable of carrying current (as you seem to
imply), it's not much use as protection.


I didn't say "incapable", I said *DOESN'T*, there is a difference.

You said the ground was not "designed to carry current." Perhaps I
read that too literally.

It's not designed to carry current. The neutral is designed to
carry current. The ground is designed to carry _fault_ current.
There are cases where the ground may be smaller than the neutral
because it's not designed to carry the return current.


I.e., what am I missing in this picture?


Faults.


No, I'm well aware of the possibility of faults.


Apparently not.

Pfft.

Well, you can't imagine faults where a washing machine case being
lit up. I can.

Won't normal GFCI functionality catch any such case that's a
significant hazard?


A parachute might catch you too, but it's a good idea to never have
rely on one.


There are already multiple levels of protection. The question is
when one stops adding more.


When one is happy with the level of protection, after all
applicable safety codes have been met.


Whatever.

Precisely then. Seat belts and air-bags are a good idea too.

--
Keith

krw wrote:

In article ,
says...

krw wrote:


In article ,
says...


krw wrote:



In article ,
says...



Jeff Wisnia wrote:




CJT wrote:




Jeff Wisnia wrote:




Goedjn wrote:




On Wed, 29 Nov 2006 16:16:40 -0500, Jeff Wisnia
wrote:





Pop` wrote:

snipped

GFI, Ground Fault Interruptor is a misnomer. "Ground" in the
original case may have been ground, but now, because of poor
terminology, is considered the Neutral conductor. How a GFCI
operates has nothing to do with the ground. Since it senses
differences in current between the hot/neutral conductors, any
third wire earth ground is irrelevant to its opeartion. Hot amps
= Neutral amps, all OK. Not equal, it trips. It's literally that
simple.

Pop`



And, don't forget that the more recent GFCI's will detect a leakage
path between the neutral and ground as well, and thus disconnect
power when there's a neutral to ground short.

Jeff





Ok, I thought I knew how GFCI outlets worked, and now I find out
that I didn't know how the test button worked. Fine, I'm ok with
that, but this doesn't make any sense. It seems as if
a nuetral-ground leak should look exactly like a hot-ground leak,
except probably smaller, as there's less resistance downstream
of the correct current path.

How would you tell the difference even if you wanted to?

--Goedjn




I didn't SAY that they tell the "difference". Since their only
"output means" is to open the circuit between the supply and load
side of the breaker for either kind of fault, hot to ground leakage
or neutral to ground shorts.

They will detect and "pop" if you make a connection between their
neutral output and ground, even with nothing at all connected to
their hot output.

Before you worry too much about how they can sense a connection
between two leads which should be at the same potential (neutral and
ground) if there isn't any current flowing in either of them, I'll
tell you that there will be, because the GFCI contains a current
transformer which adds a small in-phase voltage to both the hot and
neutral output leads.



... which suggests it won't work unless/until something is drawing
current from the "hot" lead. I realize that's not much of a
restriction.


Nope, there's a 120 volt "primary" on that "current transformer" which
is connected across the incoming line.

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ ^^^^^^^^^^^^^^^^^^^^^HERE!



The incoming hot and neutral

leads to the GFCI are "secondaries" on that transformer, and a small
amount of in phase voltage gets "added" in series to both of them. Then,
those leads continue through the normal differential current sensing
transformer and on to the "load" side of the GFCI.

My calling it a "current transformer" may not be exactly correct, but
they are transformers having one winding with lots of turns of fine wire
and two winding of wire heavy enough to carry the rated current of the
GFCI.

Now I understand. It was the terminology that threw me off. "Current
transformer" means something a bit different to me.


Ok, what does it mean to you? GFCI indeed do use current
transformers to detect the imbalance in current between the hot an
neutral.


But that's not the section of the GFCI we were discussing. In what
sense is it a "current transformer" if it has a primary connected
between hot and neutral?


Primary connected between hot and neutral? What _are_ you talking
about?

The portion of the thread identified above.


Your writing isn't clear. The current transformer is a current
transformer, no more, no less. "Primary" of what?


If you go back through the thread, you'll at some point find a link
to a page with a circuit diagram that relates to this. It shows the
portion you're thinking of, but also an additional transformer for
injecting sense current into the neutral. I can't help it if you came
in late and choose to argue with incomplete knowledge.


The hot and neutral have separate "windings". The current imbalance
is sensed with a third "winding". WHen the current in each of the
hot and neutral is the same the magnetic fields cancel, thus
nothing on the sense winding. If there is a current imbalance
there is a net magnetic field and is sensed. It is the difference
in current that's sensed, thus a current transformer.


That's a different part of the device, like I said.


That's pretty much the *entire* device.

Nope. See the link.


Regardless, that seems like an awful lot of technology to throw at a
problem that doesn't seem (to me) like much of a problem.


A fault to ground isn't a big deal to you? boggle

I fail to see how a fault between ground and neutral (of the sort we
were discussing) downstream of a GFCI, without some additional fault,
will get you electrocuted.


If there is a neutral fault you're now in the circuit. This isn't
a healthy idea.


But is it life threatening? Unlikely.


120V on the case isn't threatening? boggle


There won't BE 120V on the case, barring another fault.

Since the



ground and neutral are tied together upstream, why is it a problem if
they're also tied together downstream?


Wow! Perhaps because a neutral is designed to carry CURRENT, and a
ground is *NOT*. THink about faults! The ground is there for
safety!

Fair enough (reserve the ground to its safety role). But you don't,
e.g., protect against faults that circumvent the GFCI.


What faults would those be?


For instance, a short across the GFCI that effectively takes it out
of the circuit.


A short across the breaker takes it out of the circuit too. So?


Yes, and there's no protection against that. So not all potential
faults are protected against, which is my point.

At some point
the addition of safety devices becomes overdone. How will a
ground-neutral fault downstream of a GFCI, without some other additional
fault, get you electrocuted?


Likely not. Do you want to take that chance though? Please leave
my wiring alone.

I don't like people taking chances with my life by talking on their
cellphones while driving, either, but that doesn't necessarily mean
there should be interlocks on their car to prevent it.


There have been enough people killed that GFCIs were written into
the code for places where they would have saved lives. It's been
said that the NEC is written in blood.

And I agree that GFCIs are a good idea.




BTW, if a ground is incapable of carrying current (as you seem to
imply), it's not much use as protection.


I didn't say "incapable", I said *DOESN'T*, there is a difference.

You said the ground was not "designed to carry current." Perhaps I
read that too literally.


It's not designed to carry current. The neutral is designed to
carry current. The ground is designed to carry _fault_ current.
There are cases where the ground may be smaller than the neutral
because it's not designed to carry the return current.

I don't think a piece of wire knows the difference between fault
current and some other current.


I.e., what am I missing in this picture?


Faults.


No, I'm well aware of the possibility of faults.


Apparently not.

Pfft.


Well, you can't imagine faults where a washing machine case being
lit up. I can.

You have no idea what I can and can not imagine.



Won't normal GFCI functionality catch any such case that's a
significant hazard?


A parachute might catch you too, but it's a good idea to never have
rely on one.


There are already multiple levels of protection. The question is
when one stops adding more.


When one is happy with the level of protection, after all
applicable safety codes have been met.


Whatever.


Precisely then. Seat belts and air-bags are a good idea too.

Sure. We agree on that. Although both seat belts and air bags have
caused deaths, too.

--
The e-mail address in our reply-to line is reversed in an attempt to
minimize spam. Our true address is of the form .

On Fri, 01 Dec 2006 11:26:08 -0500, Jeff Wisnia
wrote:

CJT wrote:

Doug Miller wrote:

In article , CJT
wrote:

But neither neutral nor ground should be more than a couple of volts
above zero potential, barring an additional fault. I can see getting
a tingle, but electrocuted?



If the current passes across the heart (e.g. hand to hand, or hand to
opposite foot), as little as twenty milliamperes can be fatal.


better be careful with those AAA batteries


You know, I have long pondered the same question, since "circuit wise"
it's hard to see why the neutral wire wouldn't serve as a reasonable
"ground" IF you neglect wiring resistance and assume that all wire
terminations, once made, will remain perfect and continuous forever.


That (neutral and ground being different) was one thing I had trouble
with in college, when taking a NEC class.

But, we know that's not always the case, and while I agree that a few
volts created by an IR drop in the return lead won't hurt you unless it
somehow "gets under your skin", if you've never stuck your tongue across
the terminals of a 9 volt "transistor radio battery", you'd be shocked,
(Even more than Captain Renault was.) to "see how that tastes."


I often do that to check batteries. I have described the taste as
being like lemon juice without the lemon.

But, consider what maybe 3 to 5 volts of neutral voltage drop with
several amps of current source driving it might do in terms of heating
up some thin strip of metal, like say a piece of Xmas tree tinsel.
(Izzat stuff still metal? It was when I was a kid.)

I bought some tinsel a couple of years ago (for 25 cents a box at an
after-season sale). It was plastic.

BTW, I remember my grandparents calling the stuff "Icicles".

That could raise its
temperature enough to start a fire.


More so if you use big lights, that get hot.

So, all things considered, especially IPIO*, I think I must agree that
the addition of safety grounding to building wiring, which occurred
sometime during my life so far, was probably a pretty good idea, as are
GFCIs.

Jeff

* IPIO: the innate perversity of inanimate objects
--
24 days until the winter solstice celebration

Mark Lloyd
http://notstupid.laughingsquid.com

"Unlike biological evolution. 'intelligent design' is
not a genuine scientific theory and, therefore, has
no place in the curriculum of our nation's public
school classes." -- Ted Kennedy

In article ,
says...
krw wrote:

In article ,
says...

krw wrote:


In article ,
says...


krw wrote:



In article ,
says...



Jeff Wisnia wrote:




CJT wrote:




Jeff Wisnia wrote:




Goedjn wrote:




On Wed, 29 Nov 2006 16:16:40 -0500, Jeff Wisnia
wrote:





Pop` wrote:

snipped

GFI, Ground Fault Interruptor is a misnomer. "Ground" in the
original case may have been ground, but now, because of poor
terminology, is considered the Neutral conductor. How a GFCI
operates has nothing to do with the ground. Since it senses
differences in current between the hot/neutral conductors, any
third wire earth ground is irrelevant to its opeartion. Hot amps
= Neutral amps, all OK. Not equal, it trips. It's literally that
simple.

Pop`



And, don't forget that the more recent GFCI's will detect a leakage
path between the neutral and ground as well, and thus disconnect
power when there's a neutral to ground short.

Jeff





Ok, I thought I knew how GFCI outlets worked, and now I find out
that I didn't know how the test button worked. Fine, I'm ok with
that, but this doesn't make any sense. It seems as if
a nuetral-ground leak should look exactly like a hot-ground leak,
except probably smaller, as there's less resistance downstream
of the correct current path.

How would you tell the difference even if you wanted to?

--Goedjn




I didn't SAY that they tell the "difference". Since their only
"output means" is to open the circuit between the supply and load
side of the breaker for either kind of fault, hot to ground leakage
or neutral to ground shorts.

They will detect and "pop" if you make a connection between their
neutral output and ground, even with nothing at all connected to
their hot output.

Before you worry too much about how they can sense a connection
between two leads which should be at the same potential (neutral and
ground) if there isn't any current flowing in either of them, I'll
tell you that there will be, because the GFCI contains a current
transformer which adds a small in-phase voltage to both the hot and
neutral output leads.



... which suggests it won't work unless/until something is drawing
current from the "hot" lead. I realize that's not much of a
restriction.


Nope, there's a 120 volt "primary" on that "current transformer" which
is connected across the incoming line.

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ ^^^^^^^^^^^^^^^^^^^^^HERE!



The incoming hot and neutral

leads to the GFCI are "secondaries" on that transformer, and a small
amount of in phase voltage gets "added" in series to both of them. Then,
those leads continue through the normal differential current sensing
transformer and on to the "load" side of the GFCI.

My calling it a "current transformer" may not be exactly correct, but
they are transformers having one winding with lots of turns of fine wire
and two winding of wire heavy enough to carry the rated current of the
GFCI.

Now I understand. It was the terminology that threw me off. "Current
transformer" means something a bit different to me.


Ok, what does it mean to you? GFCI indeed do use current
transformers to detect the imbalance in current between the hot an
neutral.


But that's not the section of the GFCI we were discussing. In what
sense is it a "current transformer" if it has a primary connected
between hot and neutral?


Primary connected between hot and neutral? What _are_ you talking
about?

The portion of the thread identified above.


Your writing isn't clear. The current transformer is a current
transformer, no more, no less. "Primary" of what?


If you go back through the thread, you'll at some point find a link
to a page with a circuit diagram that relates to this. It shows the
portion you're thinking of, but also an additional transformer for
injecting sense current into the neutral.

Yes, I now see that.

I can't help it if you came
in late and choose to argue with incomplete knowledge.

You really don't have to be a prick about it.

snip


But is it life threatening? Unlikely.


120V on the case isn't threatening? boggle


There won't BE 120V on the case, barring another fault.

A ground-neutral fault can be there for *years* unnoticed. You
don't think it's a good thing to call this fault out. A neutral
fault isn't a stretch of the imagination after years. IMO, a
ground-neutral fault is worth knowing about. Obviously someone has
been killed because of this fault. It's a nickle's worth of
hardware, so?

Since the



ground and neutral are tied together upstream, why is it a problem if
they're also tied together downstream?


Wow! Perhaps because a neutral is designed to carry CURRENT, and a
ground is *NOT*. THink about faults! The ground is there for
safety!

Fair enough (reserve the ground to its safety role). But you don't,
e.g., protect against faults that circumvent the GFCI.


What faults would those be?


For instance, a short across the GFCI that effectively takes it out
of the circuit.


A short across the breaker takes it out of the circuit too. So?


Yes, and there's no protection against that. So not all potential
faults are protected against, which is my point.

The point is to try to find the discoverable faults, particularly
those that have actually killed people. If it's a nickle's worth
of silicon, who cares?

At some point
the addition of safety devices becomes overdone. How will a
ground-neutral fault downstream of a GFCI, without some other additional
fault, get you electrocuted?


Likely not. Do you want to take that chance though? Please leave
my wiring alone.

I don't like people taking chances with my life by talking on their
cellphones while driving, either, but that doesn't necessarily mean
there should be interlocks on their car to prevent it.


There have been enough people killed that GFCIs were written into
the code for places where they would have saved lives. It's been
said that the NEC is written in blood.

And I agree that GFCIs are a good idea.

THen where's your beef?



BTW, if a ground is incapable of carrying current (as you seem to
imply), it's not much use as protection.


I didn't say "incapable", I said *DOESN'T*, there is a difference.

You said the ground was not "designed to carry current." Perhaps I
read that too literally.


It's not designed to carry current. The neutral is designed to
carry current. The ground is designed to carry _fault_ current.
There are cases where the ground may be smaller than the neutral
because it's not designed to carry the return current.

I don't think a piece of wire knows the difference between fault
current and some other current.

No, but the engineer does and designs the system so that the
current goes where it's supposed to and if it goes elsewhere, shut
it down!


I.e., what am I missing in this picture?


Faults.


No, I'm well aware of the possibility of faults.


Apparently not.

Pfft.


Well, you can't imagine faults where a washing machine case being
lit up. I can.

You have no idea what I can and can not imagine.

Your crystal ball has been showing some fog here.


Won't normal GFCI functionality catch any such case that's a
significant hazard?


A parachute might catch you too, but it's a good idea to never have
rely on one.


There are already multiple levels of protection. The question is
when one stops adding more.


When one is happy with the level of protection, after all
applicable safety codes have been met.


Whatever.


Precisely then. Seat belts and air-bags are a good idea too.

Sure. We agree on that. Although both seat belts and air bags have
caused deaths, too.

Generaly when not used properly, though I don't know of a GFCI
that's killed anyone.

--
Keith

krw wrote:
In article ,
says...

krw wrote:


In article ,
says...


krw wrote:



In article ,
says...



krw wrote:




In article ,
says...




Jeff Wisnia wrote:





CJT wrote:





Jeff Wisnia wrote:





Goedjn wrote:





On Wed, 29 Nov 2006 16:16:40 -0500, Jeff Wisnia
wrote:






Pop` wrote:

snipped

GFI, Ground Fault Interruptor is a misnomer. "Ground" in the
original case may have been ground, but now, because of poor
terminology, is considered the Neutral conductor. How a GFCI
operates has nothing to do with the ground. Since it senses
differences in current between the hot/neutral conductors, any
third wire earth ground is irrelevant to its opeartion. Hot amps
= Neutral amps, all OK. Not equal, it trips. It's literally that
simple.

Pop`



And, don't forget that the more recent GFCI's will detect a leakage
path between the neutral and ground as well, and thus disconnect
power when there's a neutral to ground short.

Jeff





Ok, I thought I knew how GFCI outlets worked, and now I find out
that I didn't know how the test button worked. Fine, I'm ok with
that, but this doesn't make any sense. It seems as if
a nuetral-ground leak should look exactly like a hot-ground leak,
except probably smaller, as there's less resistance downstream
of the correct current path.

How would you tell the difference even if you wanted to?

--Goedjn




I didn't SAY that they tell the "difference". Since their only
"output means" is to open the circuit between the supply and load
side of the breaker for either kind of fault, hot to ground leakage
or neutral to ground shorts.

They will detect and "pop" if you make a connection between their
neutral output and ground, even with nothing at all connected to
their hot output.

Before you worry too much about how they can sense a connection
between two leads which should be at the same potential (neutral and
ground) if there isn't any current flowing in either of them, I'll
tell you that there will be, because the GFCI contains a current
transformer which adds a small in-phase voltage to both the hot and
neutral output leads.



... which suggests it won't work unless/until something is drawing
current from the "hot" lead. I realize that's not much of a
restriction.


Nope, there's a 120 volt "primary" on that "current transformer" which
is connected across the incoming line.

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ ^^^^^^^^^^^^^^^^^^^^^^^HERE!



The incoming hot and neutral


leads to the GFCI are "secondaries" on that transformer, and a small
amount of in phase voltage gets "added" in series to both of them. Then,
those leads continue through the normal differential current sensing
transformer and on to the "load" side of the GFCI.

My calling it a "current transformer" may not be exactly correct, but
they are transformers having one winding with lots of turns of fine wire
and two winding of wire heavy enough to carry the rated current of the
GFCI.

Now I understand. It was the terminology that threw me off. "Current
transformer" means something a bit different to me.


Ok, what does it mean to you? GFCI indeed do use current
transformers to detect the imbalance in current between the hot an
neutral.


But that's not the section of the GFCI we were discussing. In what
sense is it a "current transformer" if it has a primary connected
between hot and neutral?


Primary connected between hot and neutral? What _are_ you talking
about?

The portion of the thread identified above.


Your writing isn't clear. The current transformer is a current
transformer, no more, no less. "Primary" of what?


If you go back through the thread, you'll at some point find a link
to a page with a circuit diagram that relates to this. It shows the
portion you're thinking of, but also an additional transformer for
injecting sense current into the neutral.


Yes, I now see that.


I can't help it if you came
in late and choose to argue with incomplete knowledge.


You really don't have to be a prick about it.


Nor have I been.

snip

But is it life threatening? Unlikely.


120V on the case isn't threatening? boggle

There won't BE 120V on the case, barring another fault.


A ground-neutral fault can be there for *years* unnoticed. You
don't think it's a good thing to call this fault out. A neutral
fault isn't a stretch of the imagination after years. IMO, a

At least you recognize it's an opinion.

ground-neutral fault is worth knowing about. Obviously someone has
been killed because of this fault.

It's not obvious at all.

It's a nickle's worth of
hardware, so?


Since the




ground and neutral are tied together upstream, why is it a problem if
they're also tied together downstream?


Wow! Perhaps because a neutral is designed to carry CURRENT, and a
ground is *NOT*. THink about faults! The ground is there for
safety!

Fair enough (reserve the ground to its safety role). But you don't,
e.g., protect against faults that circumvent the GFCI.


What faults would those be?


For instance, a short across the GFCI that effectively takes it out
of the circuit.


A short across the breaker takes it out of the circuit too. So?


Yes, and there's no protection against that. So not all potential
faults are protected against, which is my point.


The point is to try to find the discoverable faults, particularly
those that have actually killed people. If it's a nickle's worth
of silicon, who cares?


At some point
the addition of safety devices becomes overdone. How will a
ground-neutral fault downstream of a GFCI, without some other additional
fault, get you electrocuted?


Likely not. Do you want to take that chance though? Please leave
my wiring alone.

I don't like people taking chances with my life by talking on their
cellphones while driving, either, but that doesn't necessarily mean
there should be interlocks on their car to prevent it.


There have been enough people killed that GFCIs were written into
the code for places where they would have saved lives. It's been
said that the NEC is written in blood.

And I agree that GFCIs are a good idea.


THen where's your beef?


Unlike another poster in this thread, I have no "beef."



BTW, if a ground is incapable of carrying current (as you seem to
imply), it's not much use as protection.


I didn't say "incapable", I said *DOESN'T*, there is a difference.

You said the ground was not "designed to carry current." Perhaps I
read that too literally.


It's not designed to carry current. The neutral is designed to
carry current. The ground is designed to carry _fault_ current.
There are cases where the ground may be smaller than the neutral
because it's not designed to carry the return current.


I don't think a piece of wire knows the difference between fault
current and some other current.


No, but the engineer does and designs the system so that the
current goes where it's supposed to and if it goes elsewhere, shut
it down!


I.e., what am I missing in this picture?


Faults.


No, I'm well aware of the possibility of faults.


Apparently not.

Pfft.


Well, you can't imagine faults where a washing machine case being
lit up. I can.

You have no idea what I can and can not imagine.


Your crystal ball has been showing some fog here.


Won't normal GFCI functionality catch any such case that's a
significant hazard?


A parachute might catch you too, but it's a good idea to never have
rely on one.


There are already multiple levels of protection. The question is
when one stops adding more.


When one is happy with the level of protection, after all
applicable safety codes have been met.


Whatever.


Precisely then. Seat belts and air-bags are a good idea too.


Sure. We agree on that. Although both seat belts and air bags have
caused deaths, too.


Generaly when not used properly, though I don't know of a GFCI
that's killed anyone.


It's not hard to construct a scenario.

--
The e-mail address in our reply-to line is reversed in an attempt to
minimize spam. Our true address is of the form .

In article ,
says...
krw wrote:
In article ,
says...

krw wrote:

big snip

There won't BE 120V on the case, barring another fault.


A ground-neutral fault can be there for *years* unnoticed. You
don't think it's a good thing to call this fault out. A neutral
fault isn't a stretch of the imagination after years. IMO, a

At least you recognize it's an opinion.

Yes, it's an opinion backed up by others.

ground-neutral fault is worth knowing about. Obviously someone has
been killed because of this fault.

It's not obvious at all.

It wouldn't be there otherwise.

Again:

It's a nickle's worth of
hardware, so?


more snippage

Precisely then. Seat belts and air-bags are a good idea too.


Sure. We agree on that. Although both seat belts and air bags have
caused deaths, too.

Saved far more.

Generaly when not used properly, though I don't know of a GFCI
that's killed anyone.


It's not hard to construct a scenario.

Please feel free.

--
Keith

krw wrote:

In article ,
says...

krw wrote:


additional snip

Generaly when not used properly, though I don't know of a GFCI
that's killed anyone.


It's not hard to construct a scenario.


Please feel free.

Have you no imagination? Think about critical power needlessly
disrupted as the result of an inconsequential fault.

--
The e-mail address in our reply-to line is reversed in an attempt to
minimize spam. Our true address is of the form .

In article ,
says...
krw wrote:

In article ,
says...

krw wrote:


additional snip

Generaly when not used properly, though I don't know of a GFCI
that's killed anyone.


It's not hard to construct a scenario.


Please feel free.

Have you no imagination? Think about critical power needlessly
disrupted as the result of an inconsequential fault.

Critical devices aren't supposed to be on GFCI protected circuits.
Try again.

--
Keith

In article , CJT wrote:
Doug Miller wrote:

In article , CJT wrote:

But neither neutral nor ground should be more than a couple of volts
above zero potential, barring an additional fault. I can see getting
a tingle, but electrocuted?


If the current passes across the heart (e.g. hand to hand, or hand to
opposite
foot), as little as twenty milliamperes can be fatal.


better be careful with those AAA batteries

DC currents don't post much of a threat to human health except at high voltage
and/or amperage; even an automobile battery (12V at several dozen amps) won't
kill, although it sure can hurt.

60 Hz AC at 120V, though, can be deadly at even 20 mA of current.

--
Regards,
Doug Miller (alphageek at milmac dot com)

It's time to throw all their damned tea in the harbor again.

krw wrote:

In article ,
says...

krw wrote:


In article ,
says...


krw wrote:


additional snip

Generaly when not used properly, though I don't know of a GFCI
that's killed anyone.


It's not hard to construct a scenario.


Please feel free.


Have you no imagination? Think about critical power needlessly
disrupted as the result of an inconsequential fault.


Critical devices aren't supposed to be on GFCI protected circuits.
Try again.

That sounds like a tacit admission that GFCIs have a downside.

--
The e-mail address in our reply-to line is reversed in an attempt to
minimize spam. Our true address is of the form .

In article ,
says...
krw wrote:

In article ,
says...

krw wrote:


In article ,
says...


krw wrote:


additional snip

Generaly when not used properly, though I don't know of a GFCI
that's killed anyone.


It's not hard to construct a scenario.


Please feel free.


Have you no imagination? Think about critical power needlessly
disrupted as the result of an inconsequential fault.


Critical devices aren't supposed to be on GFCI protected circuits.
Try again.

That sounds like a tacit admission that GFCIs have a downside.

Sheesh!

--
Keith