I recently added on a 3rd garage stall which I will use the majority of
it as a woodworking shop. To save some money I did the wiring myself.
Here is my situation.

I wanted two 20 amp circuits alternating from outlet to outlet as you
go around the shop. I ran 12/3 wire from my breaker box (new
Cutler-Hammer with Type CH breakers) to the garage and alternated red
and black wires to alternate circuits. I intended to install a GFCI
outlet at the beginning of each circuit. The inspector pointed out
that sharing one neutral between the two circuits would cause both GFCI
to trip at the same time. I asked if I should re-wire and he said I
could get a 2 pole GFCI breaker to protect both circuits.

My questions...

1. Can I still go with 2 GFCI outlets and deal with the inconvenience
of both tripping at the same time? Is there any risk in that setup?
2. Wouldn't a 2 pole GFCI breaker be producing 40 amps or am I missing
something?

Help!
Thanks in advance
Russ

"amateur_russ" wrote in message
oups.com...
I recently added on a 3rd garage stall which I will use the majority of
it as a woodworking shop. To save some money I did the wiring myself.
Here is my situation.

I wanted two 20 amp circuits alternating from outlet to outlet as you
go around the shop. I ran 12/3 wire from my breaker box (new
Cutler-Hammer with Type CH breakers) to the garage and alternated red
and black wires to alternate circuits. I intended to install a GFCI
outlet at the beginning of each circuit. The inspector pointed out
that sharing one neutral between the two circuits would cause both GFCI
to trip at the same time. I asked if I should re-wire and he said I
could get a 2 pole GFCI breaker to protect both circuits.

My questions...

1. Can I still go with 2 GFCI outlets and deal with the inconvenience
of both tripping at the same time? Is there any risk in that setup?
2. Wouldn't a 2 pole GFCI breaker be producing 40 amps or am I missing
something?

Help!
Thanks in advance
Russ

Shared neutrals will be a problem, usually when there is a load pulled from
both circuits at the same time. If you only use one circuit at a time you
might have infrequent tripping.

The only way a 2 pole breaker is giving out 40 amps is if it is a 40 amp
breaker.

I suggest that you get 20 amp GFCI's my little buzz box wire feed welder, is
hard on the 15 amp varity.

"SQLit" wrote in message
...

"amateur_russ" wrote in message
oups.com...
I recently added on a 3rd garage stall which I will use the majority of
it as a woodworking shop. To save some money I did the wiring myself.
Here is my situation.

I wanted two 20 amp circuits alternating from outlet to outlet as you
go around the shop. I ran 12/3 wire from my breaker box (new
Cutler-Hammer with Type CH breakers) to the garage and alternated red
and black wires to alternate circuits. I intended to install a GFCI
outlet at the beginning of each circuit. The inspector pointed out
that sharing one neutral between the two circuits would cause both GFCI
to trip at the same time. I asked if I should re-wire and he said I
could get a 2 pole GFCI breaker to protect both circuits.

My questions...

1. Can I still go with 2 GFCI outlets and deal with the inconvenience
of both tripping at the same time? Is there any risk in that setup?


Do you really want to install something half-ass that will continue to give
you problems? The alternative to a two pole 20 amp GFCI circuit breaker
would be to install a pigtailed GFCI receptacle at every location. That
would alleviate the unbalance problem.


2. Wouldn't a 2 pole GFCI breaker be producing 40 amps or am I missing
something?


You're missing something.



Help!
Thanks in advance
Russ

Shared neutrals will be a problem, usually when there is a load pulled
from
both circuits at the same time. If you only use one circuit at a time you
might have infrequent tripping.

The only way a 2 pole breaker is giving out 40 amps is if it is a 40 amp
breaker.

I suggest that you get 20 amp GFCI's my little buzz box wire feed welder,
is
hard on the 15 amp varity.

SQLit wrote:
Shared neutrals will be a problem, usually when there is a load pulled from
both circuits at the same time. If you only use one circuit at a time you
might have infrequent tripping.

The only way a 2 pole breaker is giving out 40 amps is if it is a 40 amp
breaker.

I suggest that you get 20 amp GFCI's my little buzz box wire feed welder, is
hard on the 15 amp varity.

Are you thinking two 20amp GFCI breakers? Don't I have the same
problem with neturals?

Thanks,
Russ

amateur_russ wrote:
I recently added on a 3rd garage stall which I will use the majority of
it as a woodworking shop. To save some money I did the wiring myself.
Here is my situation.

I wanted two 20 amp circuits alternating from outlet to outlet as you
go around the shop. I ran 12/3 wire from my breaker box (new
Cutler-Hammer with Type CH breakers) to the garage and alternated red
and black wires to alternate circuits. I intended to install a GFCI
outlet at the beginning of each circuit. The inspector pointed out
that sharing one neutral between the two circuits would cause both GFCI
to trip at the same time. I asked if I should re-wire and he said I
could get a 2 pole GFCI breaker to protect both circuits.

My questions...

1. Can I still go with 2 GFCI outlets and deal with the inconvenience
of both tripping at the same time? Is there any risk in that setup?
2. Wouldn't a 2 pole GFCI breaker be producing 40 amps or am I missing
something?

Help!
Thanks in advance
Russ



1) Use a regular 2-pole 20A breaker instead of a GFCI unless there you
have some other code requirement for GFCI breakers.

2) Start over from the 1st outlet in the garage. Use a deep double-gang
box and install *two* GFCI's. Put one on the black wire and one on the
red white and the white goes to the LINE side of both.

3) Connect a 12/2 cable to the LOAD side of each GFCI, and run these
12/2 cables to the rest of the outlets (alternating as you go).

4) It's a lot simpler than it sounds! ;-)

Bob

No, One double pole 20 amp GFCI circuit breaker and you won't have neutral
problems



"amateur_russ" wrote in message
oups.com...

SQLit wrote:
Shared neutrals will be a problem, usually when there is a load pulled
from
both circuits at the same time. If you only use one circuit at a time
you
might have infrequent tripping.

The only way a 2 pole breaker is giving out 40 amps is if it is a 40 amp
breaker.

I suggest that you get 20 amp GFCI's my little buzz box wire feed welder,
is
hard on the 15 amp varity.

Are you thinking two 20amp GFCI breakers? Don't I have the same
problem with neturals?

Thanks,
Russ

According to amateur_russ :

I wanted two 20 amp circuits alternating from outlet to outlet as you
go around the shop. I ran 12/3 wire from my breaker box (new
Cutler-Hammer with Type CH breakers) to the garage and alternated red
and black wires to alternate circuits. I intended to install a GFCI
outlet at the beginning of each circuit. The inspector pointed out
that sharing one neutral between the two circuits would cause both GFCI
to trip at the same time. I asked if I should re-wire and he said I
could get a 2 pole GFCI breaker to protect both circuits.

My questions...

1. Can I still go with 2 GFCI outlets and deal with the inconvenience
of both tripping at the same time? Is there any risk in that setup?

You misunderstood him. You _cannot_ use two independent GFCIs with
a shared neutral circuit. It just _won't_ work at all, period.

He didn't mean "trips at the same time", he meant "they _both_ will
trip" continuously.

The reason for this is simple: the hot and neutral current though
_each_ GFCI must exactly balance. But in a shared neutral circuit,
the current through the neutral is the _difference_ between the
two hot legs. So as soon as you plug _anything_ into any one of these
outlets, both GFCIs will trip.

2. Wouldn't a 2 pole GFCI breaker be producing 40 amps or am I missing
something?

Yes.

You don't understand 240V multiwire circuits.

You simply need a 2-pole 20A GFCI breaker. It's the same thing as two
independent 20A breakers, except that the poles are tied together so they
both trip at the same time. And it has a GFCI function too.

MAKE SURE that the poles are on opposite legs of the main panel. If the
current breakers aren't on opposite legs (best: adjacent to each other),
you're going to overcurrent the neutral.
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.

"RBM" rbm2(remove wrote in message
...
No, One double pole 20 amp GFCI circuit breaker and you won't have neutral
problems


I'm wondering if that is a viable solution. If he has a 5 amp drill
connected to phase A and a 1 amp shop light on phase B, won't the imbalance
on the hot legs cause the two pole GFCI breaker to trip?






"amateur_russ" wrote in message
oups.com...

SQLit wrote:
Shared neutrals will be a problem, usually when there is a load pulled
from
both circuits at the same time. If you only use one circuit at a time
you
might have infrequent tripping.

The only way a 2 pole breaker is giving out 40 amps is if it is a 40
amp
breaker.

I suggest that you get 20 amp GFCI's my little buzz box wire feed
welder,
is
hard on the 15 amp varity.

Are you thinking two 20amp GFCI breakers? Don't I have the same
problem with neturals?

Thanks,
Russ

I wouldn't think so, as some hot tubs have "main" gfci protection feeding
assorted 240 and 120 volt pumps, blowers, and heaters



"John Grabowski" wrote in message
...

"RBM" rbm2(remove wrote in message
...
No, One double pole 20 amp GFCI circuit breaker and you won't have
neutral
problems


I'm wondering if that is a viable solution. If he has a 5 amp drill
connected to phase A and a 1 amp shop light on phase B, won't the
imbalance
on the hot legs cause the two pole GFCI breaker to trip?






"amateur_russ" wrote in message
oups.com...

SQLit wrote:
Shared neutrals will be a problem, usually when there is a load pulled
from
both circuits at the same time. If you only use one circuit at a time
you
might have infrequent tripping.

The only way a 2 pole breaker is giving out 40 amps is if it is a 40
amp
breaker.

I suggest that you get 20 amp GFCI's my little buzz box wire feed
welder,
is
hard on the 15 amp varity.

Are you thinking two 20amp GFCI breakers? Don't I have the same
problem with neturals?

Thanks,
Russ

On Tue, 31 Jan 2006 11:46:39 -0700, "SQLit" wrote:


"amateur_russ" wrote in message
roups.com...
I recently added on a 3rd garage stall which I will use the majority of
it as a woodworking shop. To save some money I did the wiring myself.
Here is my situation.

I wanted two 20 amp circuits alternating from outlet to outlet as you
go around the shop. I ran 12/3 wire from my breaker box (new
Cutler-Hammer with Type CH breakers) to the garage and alternated red
and black wires to alternate circuits. I intended to install a GFCI
outlet at the beginning of each circuit. The inspector pointed out
that sharing one neutral between the two circuits would cause both GFCI
to trip at the same time. I asked if I should re-wire and he said I
could get a 2 pole GFCI breaker to protect both circuits.

My questions...

1. Can I still go with 2 GFCI outlets and deal with the inconvenience
of both tripping at the same time? Is there any risk in that setup?
2. Wouldn't a 2 pole GFCI breaker be producing 40 amps or am I missing
something?

Help!
Thanks in advance
Russ

Shared neutrals will be a problem, usually when there is a load pulled from
both circuits at the same time. If you only use one circuit at a time you
might have infrequent tripping.

The only way a 2 pole breaker is giving out 40 amps is if it is a 40 amp
breaker.


Some people would add the 20 on one pole and the 20 on the other to
get 40, without realizing that this doesn't correspond to reality
(considering different phases). Like those 3 12-year-old boys who
thought they were 36 together.

I suggest that you get 20 amp GFCI's my little buzz box wire feed welder, is
hard on the 15 amp varity.

--
Mark Lloyd
http://notstupid.laughingsquid.com

"Democracy is two wolves and a lamb voting on what
to have for lunch. Liberty is a well armed lamb
contesting the vote." - Benjamin Franklin

On 31 Jan 2006 11:31:31 -0800, "amateur_russ"
wrote:


SQLit wrote:
Shared neutrals will be a problem, usually when there is a load pulled from
both circuits at the same time. If you only use one circuit at a time you
might have infrequent tripping.

The only way a 2 pole breaker is giving out 40 amps is if it is a 40 amp
breaker.

I suggest that you get 20 amp GFCI's my little buzz box wire feed welder, is
hard on the 15 amp varity.

Are you thinking two 20amp GFCI breakers? Don't I have the same
problem with neturals?


Looks like you will if you do, you won't if you don't.

The neutrals will always be shared before the GFCIs (line side). I
expect that the previously mentioned problem had to do with sharing
neutrals after the GFCIs (load side).

Thanks,
Russ
--
Mark Lloyd
http://notstupid.laughingsquid.com

"Democracy is two wolves and a lamb voting on what
to have for lunch. Liberty is a well armed lamb
contesting the vote." - Benjamin Franklin

On Tue, 31 Jan 2006 16:27:17 -0500, "RBM" rbm2(remove
wrote:

No, One double pole 20 amp GFCI circuit breaker and you won't have neutral
problems


If sharing neutral before the GFCIs (line side) is causing a problem,
you won't have eliminated it. The design of breaker boxes (and
connections to the street) has a single neutral.



"amateur_russ" wrote in message
roups.com...

SQLit wrote:
Shared neutrals will be a problem, usually when there is a load pulled
from
both circuits at the same time. If you only use one circuit at a time
you
might have infrequent tripping.

The only way a 2 pole breaker is giving out 40 amps is if it is a 40 amp
breaker.

I suggest that you get 20 amp GFCI's my little buzz box wire feed welder,
is
hard on the 15 amp varity.

Are you thinking two 20amp GFCI breakers? Don't I have the same
problem with neturals?

Thanks,
Russ


--
Mark Lloyd
http://notstupid.laughingsquid.com

"Democracy is two wolves and a lamb voting on what
to have for lunch. Liberty is a well armed lamb
contesting the vote." - Benjamin Franklin

On Tue, 31 Jan 2006 18:22:23 -0500, "John Grabowski"
wrote:


"RBM" rbm2(remove wrote in message
...
No, One double pole 20 amp GFCI circuit breaker and you won't have neutral
problems


I'm wondering if that is a viable solution. If he has a 5 amp drill
connected to phase A and a 1 amp shop light on phase B, won't the imbalance
on the hot legs cause the two pole GFCI breaker to trip?



It would if the GFCI is miswired.





"amateur_russ" wrote in message
oups.com...

SQLit wrote:
Shared neutrals will be a problem, usually when there is a load pulled
from
both circuits at the same time. If you only use one circuit at a time
you
might have infrequent tripping.

The only way a 2 pole breaker is giving out 40 amps is if it is a 40
amp
breaker.

I suggest that you get 20 amp GFCI's my little buzz box wire feed
welder,
is
hard on the 15 amp varity.

Are you thinking two 20amp GFCI breakers? Don't I have the same
problem with neturals?

Thanks,
Russ



--
Mark Lloyd
http://notstupid.laughingsquid.com

"Democracy is two wolves and a lamb voting on what
to have for lunch. Liberty is a well armed lamb
contesting the vote." - Benjamin Franklin

On Tue, 31 Jan 2006 22:54:21 -0000, (Chris
Lewis) wrote:

According to amateur_russ :

I wanted two 20 amp circuits alternating from outlet to outlet as you
go around the shop. I ran 12/3 wire from my breaker box (new
Cutler-Hammer with Type CH breakers) to the garage and alternated red
and black wires to alternate circuits. I intended to install a GFCI
outlet at the beginning of each circuit. The inspector pointed out
that sharing one neutral between the two circuits would cause both GFCI
to trip at the same time. I asked if I should re-wire and he said I
could get a 2 pole GFCI breaker to protect both circuits.

My questions...

1. Can I still go with 2 GFCI outlets and deal with the inconvenience
of both tripping at the same time? Is there any risk in that setup?

You misunderstood him. You _cannot_ use two independent GFCIs with
a shared neutral circuit. It just _won't_ work at all, period.

He didn't mean "trips at the same time", he meant "they _both_ will
trip" continuously.


This would apply to sharing a neutral on the LOAD side of the GFCIs
(you have to have a separate neutral for each here). Sharing a neutral
on the LINE side shouldn't cause anything like this. I think people
are having trouble because they're getting these mixed up.

The reason for this is simple: the hot and neutral current though
_each_ GFCI must exactly balance.

This limitation does not apply to the wiring supplying power TO the
GFCIs.

But in a shared neutral circuit,
the current through the neutral is the _difference_ between the
two hot legs. So as soon as you plug _anything_ into any one of these
outlets, both GFCIs will trip.

2. Wouldn't a 2 pole GFCI breaker be producing 40 amps or am I missing
something?

Yes.

You don't understand 240V multiwire circuits.

You simply need a 2-pole 20A GFCI breaker. It's the same thing as two
independent 20A breakers, except that the poles are tied together so they
both trip at the same time. And it has a GFCI function too.

MAKE SURE that the poles are on opposite legs of the main panel. If the
current breakers aren't on opposite legs (best: adjacent to each other),
you're going to overcurrent the neutral.

A double-pole breaker wouldn't let you get it wrong (at least not
without some extra work).
--
Mark Lloyd
http://notstupid.laughingsquid.com

"Democracy is two wolves and a lamb voting on what
to have for lunch. Liberty is a well armed lamb
contesting the vote." - Benjamin Franklin

Imbalance won't be a problem with a twopole GFCI breaker. Confusion
comes from this statement:
The reason for this is simple: the hot and neutral current though
_each_ GFCI must exactly balance.

This is true, but not the way the GFCI works. The GFCI has a special
ring through which both the hot and neutral wires run. Like a circus
lion jumping through a hoop. The ring senses the sum of the current
running through it, and the GFCI trips if this sum is ever more than
5ma (in either direction: up or downstream). The only way to keep the
sum of the currents zero is obviously to have both hot and neutral
exactly the same current, but in opposite directions.

The double-pole GFCI breaker just runs both hots and the single neutral
through the same single ring. In your example, you get 5amp phase A on
one hot, 1amp phase B on the second hot, and negative (5amp A + 1amp B)
on the neutral. Course, since phase A is exactly the negative of phase
B, that's really 5ampA on one hot, -1ampA on other hot, and -4ampA on
the neutral. And wonder of wonders if it doesn't sum up to zero so the
breaker doesn't trip.

-Kevin

"kevin" wrote in message
oups.com...
Imbalance won't be a problem with a twopole GFCI breaker. Confusion
comes from this statement:
The reason for this is simple: the hot and neutral current though
_each_ GFCI must exactly balance.

This is true, but not the way the GFCI works. The GFCI has a special
ring through which both the hot and neutral wires run. Like a circus
lion jumping through a hoop. The ring senses the sum of the current
running through it, and the GFCI trips if this sum is ever more than
5ma (in either direction: up or downstream). The only way to keep the
sum of the currents zero is obviously to have both hot and neutral
exactly the same current, but in opposite directions.

The double-pole GFCI breaker just runs both hots and the single neutral
through the same single ring. In your example, you get 5amp phase A on
one hot, 1amp phase B on the second hot, and negative (5amp A + 1amp B)
on the neutral. Course, since phase A is exactly the negative of phase
B, that's really 5ampA on one hot, -1ampA on other hot, and -4ampA on
the neutral. And wonder of wonders if it doesn't sum up to zero so the
breaker doesn't trip.

-Kevin


Thanks for the explanation Kevin. I never installed a two pole GFCI breaker
like the original poster intends to so I had no personal experience as to
whether it would work or not. Your example makes perfect sense.

According to kevin :
Imbalance won't be a problem with a twopole GFCI breaker. Confusion
comes from this statement:
The reason for this is simple: the hot and neutral current though
_each_ GFCI must exactly balance.

This is true, but not the way the GFCI works.

Actually it is. The whole point of the toroidal coil is to detect
when they imbalance. With a two pole GFCI, the coil's just wired
differently so that they detect when the neutral current isn't
the difference between the two hot currents.

If you tried to do a multi-wire branch circuit with two single pole
GFCIs, the toroids (plural) aren't wired right to detect imbalance
properly. So they be tripped all the time.
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.

According to Mark Lloyd :
On Tue, 31 Jan 2006 16:27:17 -0500, "RBM" rbm2(remove
wrote:

No, One double pole 20 amp GFCI circuit breaker and you won't have neutral
problems


If sharing neutral before the GFCIs (line side) is causing a problem,
you won't have eliminated it. The design of breaker boxes (and
connections to the street) has a single neutral.

Sharing the neutral _after_ the GFCIs (load side) is what causes the
problems.

It's perfectly reasonable to put two gfci's on the end of a 4 wire 240V
circuit, but the neutrals on the load side of the GFCIs MUST NOT connect
to each other in any way.
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.

According to Mark Lloyd :
On Tue, 31 Jan 2006 22:54:21 -0000, (Chris
Lewis) wrote:

He didn't mean "trips at the same time", he meant "they _both_ will
trip" continuously.

This would apply to sharing a neutral on the LOAD side of the GFCIs
(you have to have a separate neutral for each here). Sharing a neutral
on the LINE side shouldn't cause anything like this. I think people
are having trouble because they're getting these mixed up.

The reason for this is simple: the hot and neutral current though
_each_ GFCI must exactly balance.

This limitation does not apply to the wiring supplying power TO the
GFCIs.

Right. I should have made that clear. But the application at hand
does share neutral on the load side fo the GFCIs.

MAKE SURE that the poles are on opposite legs of the main panel. If the
current breakers aren't on opposite legs (best: adjacent to each other),
you're going to overcurrent the neutral.

A double-pole breaker wouldn't let you get it wrong (at least not
without some extra work).

Heh. Depends on the panel. It is quite possible to install a FPE
double-pole breaker into a FPE panel such that _both_ poles are on the
same leg.

Or at least it was about 15 years ago ;-)
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.

On Fri, 03 Feb 2006 21:07:48 -0000, (Chris
Lewis) wrote:

According to Mark Lloyd :
On Tue, 31 Jan 2006 16:27:17 -0500, "RBM" rbm2(remove
wrote:

No, One double pole 20 amp GFCI circuit breaker and you won't have neutral
problems


If sharing neutral before the GFCIs (line side) is causing a problem,
you won't have eliminated it. The design of breaker boxes (and
connections to the street) has a single neutral.

Sharing the neutral _after_ the GFCIs (load side) is what causes the
problems.

It's perfectly reasonable to put two gfci's on the end of a 4 wire 240V
circuit, but the neutrals on the load side of the GFCIs MUST NOT connect
to each other in any way.

Something I posted a few times recently. Those posts were ignored.
--
Mark Lloyd
http://notstupid.laughingsquid.com

"Democracy is two wolves and a lamb voting on what
to have for lunch. Liberty is a well armed lamb
contesting the vote." - Benjamin Franklin

Chris Lewis wrote:
According to kevin :
Imbalance won't be a problem with a twopole GFCI breaker. Confusion
comes from this statement:
The reason for this is simple: the hot and neutral current though
_each_ GFCI must exactly balance.

This is true, but not the way the GFCI works.

Actually it is. The whole point of the toroidal coil is to detect
when they imbalance. With a two pole GFCI, the coil's just wired
differently so that they detect when the neutral current isn't
the difference between the two hot currents.

Sorry, I think my point was misunderstood. I was trying to point out
that a GFCI has no special circuitry to examine the neutral current and
the hot current and compare them. That is, the "toroidal coil" doesn't
distinguish between hot, neutral, phases, whatever. Instead, it simply
detects the net sum of all current passing through the coil. As you
know, a one pole GFCI has two wires going through the coil, and a
two-pole GFCI has three wires going through. Or, rather, in fact they
would have an extra wire each for the test button, which leaks a bit of
current through in one direction, then loops it around back to the
supply side without going back through the coil. But the coil could
care less about neutrals, hots, phases, or whatever. Talking about
"balances", "comparing", etc, can be misleading. Talking about total
current seems to me a much more useful way of thinking about a GFCI
(since it avoids the one-pole two-pole confusion), and is a description
much closer to what the circuit actually implements.


If you tried to do a multi-wire branch circuit with two single pole
GFCIs, the toroids (plural) aren't wired right to detect imbalance
properly. So they be tripped all the time.

Yup.

According to kevin :

Chris Lewis wrote:
According to kevin :
Imbalance won't be a problem with a twopole GFCI breaker. Confusion
comes from this statement:
The reason for this is simple: the hot and neutral current though
_each_ GFCI must exactly balance.

This is true, but not the way the GFCI works.

Actually it is. The whole point of the toroidal coil is to detect
when they imbalance. With a two pole GFCI, the coil's just wired
differently so that they detect when the neutral current isn't
the difference between the two hot currents.

Sorry, I think my point was misunderstood. I was trying to point out
that a GFCI has no special circuitry to examine the neutral current and
the hot current and compare them. That is, the "toroidal coil" doesn't
distinguish between hot, neutral, phases, whatever. Instead, it simply
detects the net sum of all current passing through the coil.

We're both saying the same thing, but I think the "must balance" terminology
is more understandable than "net sum".

Balance says much more directly what the device is looking for, which
in these sorts of discussions is more important than implementation
details.

"Balance" meaning "discrete measurement" is more a digital concept.

Obviously, there's no need to have a microcomputer in a GFCI.

People forget about analog.

Talking about
"balances", "comparing", etc, can be misleading. Talking about total
current seems to me a much more useful way of thinking about a GFCI
(since it avoids the one-pole two-pole confusion), and is a description
much closer to what the circuit actually implements.

"Total current" is only going to make sense to people who can think
in phases (or worse, vector math, and remember the left-hand-rule ;-)
Otherwise, most people are going to get confused about the "zero sum"
methodology in the toroid and come out with "How can it be zero (and
not trip) when you're drawing current, you moron!" ;-)
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.

On Mon, 06 Feb 2006 21:51:09 -0000, (Chris
Lewis) wrote:

According to kevin :

Chris Lewis wrote:
According to kevin :
Imbalance won't be a problem with a twopole GFCI breaker. Confusion
comes from this statement:
The reason for this is simple: the hot and neutral current though
_each_ GFCI must exactly balance.

This is true, but not the way the GFCI works.

Actually it is. The whole point of the toroidal coil is to detect
when they imbalance. With a two pole GFCI, the coil's just wired
differently so that they detect when the neutral current isn't
the difference between the two hot currents.

Sorry, I think my point was misunderstood. I was trying to point out
that a GFCI has no special circuitry to examine the neutral current and
the hot current and compare them. That is, the "toroidal coil" doesn't
distinguish between hot, neutral, phases, whatever. Instead, it simply
detects the net sum of all current passing through the coil.

We're both saying the same thing, but I think the "must balance" terminology
is more understandable than "net sum".

Balance says much more directly what the device is looking for, which
in these sorts of discussions is more important than implementation
details.

"Balance" meaning "discrete measurement" is more a digital concept.

Obviously, there's no need to have a microcomputer in a GFCI.

People forget about analog.


They do. Analog can work quite well for special-purpose devices.

Talking about
"balances", "comparing", etc, can be misleading. Talking about total
current seems to me a much more useful way of thinking about a GFCI
(since it avoids the one-pole two-pole confusion), and is a description
much closer to what the circuit actually implements.

"Total current" is only going to make sense to people who can think
in phases (or worse, vector math, and remember the left-hand-rule ;-)
Otherwise, most people are going to get confused about the "zero sum"
methodology in the toroid and come out with "How can it be zero (and
not trip) when you're drawing current, you moron!" ;-)

The total current (through a properly wired and non-tripping GFCI)
will be zero, although I expect a lot of people to fail to understand
that.

In the same way, the total current in a 3-phase wye is zero.
--
Mark Lloyd
http://notstupid.laughingsquid.com

"Democracy is two wolves and a lamb voting on what
to have for lunch. Liberty is a well armed lamb
contesting the vote." - Benjamin Franklin

According to Mark Lloyd :

The total current (through a properly wired and non-tripping GFCI)
will be zero, although I expect a lot of people to fail to understand
that.

Including me. Unless I had prewarning you were speaking in net sum
terms. Otherwise, obviously, the total current is what is passing
through a wire.
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.

On Wed, 08 Feb 2006 07:36:10 -0000, (Chris
Lewis) wrote:

According to Mark Lloyd :

The total current (through a properly wired and non-tripping GFCI)
will be zero, although I expect a lot of people to fail to understand
that.

Including me. Unless I had prewarning you were speaking in net sum
terms. Otherwise, obviously, the total current is what is passing
through a wire.

Of course, there's more than 1 wire in there, and I did say "total".
--
Mark Lloyd
http://notstupid.laughingsquid.com

"Democracy is two wolves and a lamb voting on what
to have for lunch. Liberty is a well armed lamb
contesting the vote." - Benjamin Franklin

According to Mark Lloyd :
On Wed, 08 Feb 2006 07:36:10 -0000, (Chris
Lewis) wrote:

According to Mark Lloyd :

The total current (through a properly wired and non-tripping GFCI)
will be zero, although I expect a lot of people to fail to understand
that.

Including me. Unless I had prewarning you were speaking in net sum
terms. Otherwise, obviously, the total current is what is passing
through a wire.

Of course, there's more than 1 wire in there, and I did say "total".

Well, yes. But you're wearing your electronics hat, not your electrical
hat.

Unless you're used to thinking of current in terms of instantaneous
_direction_, and think that the hot current is balancing (and in opposite
direction) to the neutral, the total isn't going to be the electronics
notion of "net current flow", it's going to be the electrical notion of
how much current the circuit is delivering to the load at the far end.

Which isn't the same thing. Of course.
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.

On Mon, 13 Feb 2006 21:40:52 -0000, (Chris
Lewis) wrote:

According to Mark Lloyd :
On Wed, 08 Feb 2006 07:36:10 -0000, (Chris
Lewis) wrote:

According to Mark Lloyd :

The total current (through a properly wired and non-tripping GFCI)
will be zero, although I expect a lot of people to fail to understand
that.

Including me. Unless I had prewarning you were speaking in net sum
terms. Otherwise, obviously, the total current is what is passing
through a wire.

Of course, there's more than 1 wire in there, and I did say "total".

Well, yes. But you're wearing your electronics hat, not your electrical
hat.

Unless you're used to thinking of current in terms of instantaneous
_direction_, and think that the hot current is balancing (and in opposite
direction) to the neutral, the total isn't going to be the electronics
notion of "net current flow", it's going to be the electrical notion of
how much current the circuit is delivering to the load at the far end.

Which isn't the same thing. Of course.

I know the difference. A GFCI is affected by the current flowing
through it, not the current flowing through the load.

BTW, it is true that I've had more electronics experience.
--
Mark Lloyd
http://notstupid.laughingsquid.com

"Democracy is two wolves and a lamb voting on what
to have for lunch. Liberty is a well armed lamb
contesting the vote." - Benjamin Franklin

According to Mark Lloyd :
On Mon, 13 Feb 2006 21:40:52 -0000, (Chris
Lewis) wrote:

Well, yes. But you're wearing your electronics hat, not your electrical
hat.

Unless you're used to thinking of current in terms of instantaneous
_direction_, and think that the hot current is balancing (and in opposite
direction) to the neutral, the total isn't going to be the electronics
notion of "net current flow", it's going to be the electrical notion of
how much current the circuit is delivering to the load at the far end.

Which isn't the same thing. Of course.

I know the difference.

I know you know. The problem is with people who don't have an electronics
hat ;-)

[The "you" in the quoted sentence wasn't supposed to be _you_, Mark, but
a generic "you". Oops. Sorry about that.]

A GFCI is affected by the current flowing
through it, not the current flowing through the load.

Sorry to belabor it, but you did it _again_, Mark ;-)

Most electrical tradespeople (and most DIYs) would be thoroughly
confused by that statement. I think an electronics person would also be.
[Unless they've been following this conversation. But, everybody's
probably ignoring us now ;-) You (generic you ;-) may catcall and
boo now ;-)]

Let's try something a little more precise - something that expresses
a electronics notion in terms understandable to "pure" electricians:

A GFCI is affected by the net sum of current flowing through the
current carrying conductors, remembering that in a circuit
without leakage, the net current flow will sum up to zero.

[Eg: in 120V circuit, the hot and neutral have equal and opposite
direction currents. In a pure 240 circuit, the same is true of
the two hots. In a 240/120V circuit, if the hots differ, the neutral
makes up the difference, and it still sums up to zero.]

A GFCI is an elegantly simple circuit.

BTW, it is true that I've had more electronics experience.

It shows ;-)
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.