On 1/12/2011 2:27 PM, DerbyDad03 wrote:
I was discussing worklights with a friend. I told him that I have one
of these 500 watt units:

http://www.harborfreight.com/500-wat...ght-40123.html

In one email he said:

"I like the idea of these lights, but every time I purchase one for
use, they trip the GFCI receptacle in my garage. I've had to return
every light that I've purchased and have given up on the idea."

When I said that I've used this light in the rain more than once
without any problem, he replied with:

"I believe that it's the pure wattage requirements of these lights,
more than their quality (or lack thereof) that caused my GFCI to
trip."

Does that make any sense?

If it was an current overage the breaker would trip not the GFCI so
why would a "high wattage" device trip the GFCI?

Actually a good question.

GFCI's do not work like fuses:

http://home.howstuffworks.com/question117.htm

Frank wrote:


http://home.howstuffworks.com/question117.htm


That article might drive the EEs here a little batty.
AC doesn't actually flow. The electrons jiggle.
I checked a few pages down and found another obvious error.
There is another mistake he http://tinyurl.com/4dv2hch
just above the watt hour meter.

On 1/12/2011 5:16 PM Dean Hoffman spake thus:

Frank wrote:

http://home.howstuffworks.com/question117.htm

That article might drive the EEs here a little batty.
AC doesn't actually flow. The electrons jiggle.
I checked a few pages down and found another obvious error.
There is another mistake he http://tinyurl.com/4dv2hch
just above the watt hour meter.

What, the step-down transformer? What's wrong with that?

And I have to disagree with you; who says AC doesn't flow? During the
positive half-cycle, current flows (electrons from negative to positive,
or "conventional current flow" in the opposite direction).

I suppose this explanation falls apart if looked at from the POV of
quantum physics, but for an explanation of current flow from an
electrical standpoint it's perfectly valid.


--
Comment on quaint Usenet customs, from Usenet:

To me, the *plonk...* reminds me of the old man at the public hearing
who stands to make his point, then removes his hearing aid as a sign
that he is not going to hear any rebuttals.

David Nebenzahl wrote:
On 1/12/2011 5:16 PM Dean Hoffman spake thus:

Frank wrote:

http://home.howstuffworks.com/question117.htm

That article might drive the EEs here a little batty.
AC doesn't actually flow. The electrons jiggle.
I checked a few pages down and found another obvious error.
There is another mistake he http://tinyurl.com/4dv2hch
just above the watt hour meter.

What, the step-down transformer? What's wrong with that?

The explanation just above it. The center tapped secondary of a
single phase transformer has two phases all of sudden.
(I'm growing up to be a picky old fart.)

And I have to disagree with you; who says AC doesn't flow? During the
positive half-cycle, current flows (electrons from negative to positive,
or "conventional current flow" in the opposite direction).

I suppose this explanation falls apart if looked at from the POV of
quantum physics, but for an explanation of current flow from an
electrical standpoint it's perfectly valid.

On Wed, 12 Jan 2011 20:02:11 -0600, Dean Hoffman
wrote:

David Nebenzahl wrote:
On 1/12/2011 5:16 PM Dean Hoffman spake thus:

Frank wrote:

http://home.howstuffworks.com/question117.htm

That article might drive the EEs here a little batty.
AC doesn't actually flow. The electrons jiggle.
I checked a few pages down and found another obvious error.
There is another mistake he http://tinyurl.com/4dv2hch
just above the watt hour meter.

What, the step-down transformer? What's wrong with that?

The explanation just above it. The center tapped secondary of a
single phase transformer has two phases all of sudden.
(I'm growing up to be a picky old fart.)

It is considered single phase. If you remove the center tap, you have
the same thing on the primary as you do on the secondary.

If you chose to put the secondary tap anywhere but the center, you
still have 240 total, but the fraction of 240 changes as you move the
center tap.

Metspitzer wrote:

It is considered single phase. If you remove the center tap, you have
the same thing on the primary as you do on the secondary.

If you chose to put the secondary tap anywhere but the center, you
still have 240 total, but the fraction of 240 changes as you move the
center tap.

This sentence is the one that doesn't ring true.
"The two insulated wires each carry 120 volts, but they are 180
degrees out of phase so the difference between them is 240 volts. "

That may not make sense to some, but it does to
me. But then, I've spent some time in front of an
oscilliscope.

--
Christopher A. Young
Learn more about Jesus
www.lds.org
..


"Dean Hoffman" wrote in message
...

This sentence is the one that doesn't ring true.
"The two insulated wires each carry 120 volts, but they
are 180
degrees out of phase so the difference between them is 240
volts. "

On Wed, 12 Jan 2011 20:54:48 -0600, Dean Hoffman
wrote:

Metspitzer wrote:

It is considered single phase. If you remove the center tap, you have
the same thing on the primary as you do on the secondary.

If you chose to put the secondary tap anywhere but the center, you
still have 240 total, but the fraction of 240 changes as you move the
center tap.

This sentence is the one that doesn't ring true.
"The two insulated wires each carry 120 volts, but they are 180
degrees out of phase so the difference between them is 240 volts. "


They are in phase, and opposite polarity. I don't even know what that
means anymore..........Never mind

On Wed, 12 Jan 2011 20:54:48 -0600, Dean Hoffman
wrote:

Metspitzer wrote:

It is considered single phase. If you remove the center tap, you have
the same thing on the primary as you do on the secondary.

If you chose to put the secondary tap anywhere but the center, you
still have 240 total, but the fraction of 240 changes as you move the
center tap.

This sentence is the one that doesn't ring true.
"The two insulated wires each carry 120 volts, but they are 180
degrees out of phase so the difference between them is 240 volts. "


There is NO PHASE DIFFERENCE on a center tapped transformer. If the
voltages were 180 degrees out, there would be 120 on each side and
ZERO voltage across the pair.

"Dean Hoffman" wrote in message
...
Metspitzer wrote:

It is considered single phase. If you remove the center tap, you have
the same thing on the primary as you do on the secondary.

If you chose to put the secondary tap anywhere but the center, you
still have 240 total, but the fraction of 240 changes as you move the
center tap.

This sentence is the one that doesn't ring true.
"The two insulated wires each carry 120 volts, but they are 180 degrees
out of phase so the difference between them is 240 volts. "




The common 240 volt system in the US is only single phase. A true 2 phase
system will have the the voltages only 90 deg out of phase. In a 240 volt
single phase system , the center, neutral or whatever you want to call the
wire will carry only the unballanced currents and can be the same size as
the other two wires. A true 2 phase system usually has 4 wires, but it it
is wired up with only 3 wires, the 'center' wire has to be the largest wire.

There are always some on here that do not understand the differance in a
split phase 120/240 volts system ususally used in the homes and a true 2
phase system. I doubt that hardly anyone here has seem a true 2 phase power
system.

wrote:
On Wed, 12 Jan 2011 20:54:48 -0600, Dean Hoffman
wrote:

This sentence is the one that doesn't ring true.
"The two insulated wires each carry 120 volts, but they are 180
degrees out of phase so the difference between them is 240 volts. "


There is NO PHASE DIFFERENCE on a center tapped transformer. If the
voltages were 180 degrees out, there would be 120 on each side and
ZERO voltage across the pair.

Which is exactly what made the little buzzer in my head go off. A
single phase can't be out of phase or out of time with itself.

In article ,
"Stormin Mormon" wrote:

I've spent some time in front of an
oscilliscope.

Was that when you were a poor black child, and your parents couldn't
afford TV?

On 1/12/2011 10:21 PM, wrote:
On Wed, 12 Jan 2011 20:54:48 -0600, Dean Hoffman
wrote:

Metspitzer wrote:

It is considered single phase. If you remove the center tap, you have
the same thing on the primary as you do on the secondary.

If you chose to put the secondary tap anywhere but the center, you
still have 240 total, but the fraction of 240 changes as you move the
center tap.

This sentence is the one that doesn't ring true.
"The two insulated wires each carry 120 volts, but they are 180
degrees out of phase so the difference between them is 240 volts. "


There is NO PHASE DIFFERENCE on a center tapped transformer. If the
voltages were 180 degrees out, there would be 120 on each side and
ZERO voltage across the pair.

I don't think you mean that. Or you have a reference different than
the center tap.

If they were in phase (relative to the tap), they would read 0. Same
as reading between two breakers on the same phase in a breaker box. It's
the same voltage, same phase hence no difference. But of course, it
isn't that way.

Put another way: When current is flowing out the top leg of the
transformer, it is flowing in the bottom leg. Opposite polarity, 180
out of phase.

I'm assuming that was just a quickie mistake and we won't be arguing
this, at least I won't be. I just wanted to correct the record for
anyone else.

For others, 240 center tapped is exactly how two 120 phases are
delivered into the home:

http://www.energyquest.ca.gov/how_it...ansformer.html

Jeff

On Jan 12, 10:22*pm, "Ralph Mowery"
wrote:
"Dean Hoffman" wrote in message

...

Metspitzer wrote:

It is considered single phase. *If you remove the center tap, you have
the same thing on the primary as you do on the secondary.

If you chose to put the secondary tap anywhere but the center, you
still have 240 total, but the fraction of 240 changes as you move the
center tap.

* *This sentence is the one that doesn't ring true.
* "The two insulated wires each carry 120 volts, but they are 180 degrees
out of phase so the difference between them is 240 volts. "

The common 240 volt system in the US is only single phase. *A true 2 phase
system will have the the voltages only 90 deg out of phase. * In a 240 volt
single phase system , the center, neutral or whatever you want to call the
wire will carry only the unballanced currents and can be the same size as
the other two wires. *A true 2 phase system usually has 4 wires, but it it
is wired up with only 3 wires, the 'center' wire has to be the largest wire.

There are always some on here that do not understand the differance in a
split phase 120/240 volts system ususally used in the homes and a true 2
phase system. *I doubt that hardly anyone here has seem a true 2 phase power
system.

Actually, both views are correct. Regardlesss of how the phase
difference
is generated, if you view the two legs of a 240V service on an
oscilloscope
the two voltages are in fact 180deg out of phase with each other.
Note that
the post that generated the discussion did not even call it a two
phase system.
It only said the two voltages in a 240V service are 180 deg out of
phase with
each other. That is correct. If they showed that picture on a EE
test and
asked "What is the phase difference between the two signals, what
would
you answer have been?"

On 1/12/2011 7:22 PM Ralph Mowery spake thus:

"Dean Hoffman" wrote in message
...

Metspitzer wrote:

It is considered single phase. If you remove the center tap, you
have the same thing on the primary as you do on the secondary.

If you chose to put the secondary tap anywhere but the center,
you still have 240 total, but the fraction of 240 changes as you
move the center tap.

This sentence is the one that doesn't ring true. "The two insulated
wires each carry 120 volts, but they are 180 degrees out of phase
so the difference between them is 240 volts. "

The common 240 volt system in the US is only single phase. A true 2 phase
system will have the the voltages only 90 deg out of phase. In a 240 volt
single phase system , the center, neutral or whatever you want to call the
wire will carry only the unballanced currents and can be the same size as
the other two wires. A true 2 phase system usually has 4 wires, but it it
is wired up with only 3 wires, the 'center' wire has to be the largest wire.

There are always some on here that do not understand the differance in a
split phase 120/240 volts system ususally used in the homes and a true 2
phase system. I doubt that hardly anyone here has seem a true 2 phase power
system.

No, I had never really known what they were until now. Just looked it
up, and it's just as you say.

I'm wondering, though, just how effective or even useful 2-phase systems
really were. If you graph the waveforms, you see that there's a hole in
it, a "missing" phase, the one that would start at 180° that's present
in a 3-phase system. So what you have is current pulses that go
"bump-bump (pause)" instead of "bump-bump-bump", right?

Apparently that's one reason that 3-phase superseded 2-phase power. It's
true that 2-phase was better than single-phase for running certain types
of induction motors.

It's a matter of semantics, I know, but the 120+120=240 system we've
been discussing actually is a 2-phase system, even though it's not
really called that. One side is 180° out of phase with the other side,
so by definition you have a 2-phase system.

Hopefully the previous poster who brought this up and was confused by
this is less so now.


--
Comment on quaint Usenet customs, from Usenet:

To me, the *plonk...* reminds me of the old man at the public hearing
who stands to make his point, then removes his hearing aid as a sign
that he is not going to hear any rebuttals.

David Nebenzahl wrote:
On 1/12/2011 5:16 PM Dean Hoffman spake thus:

Frank wrote:

http://home.howstuffworks.com/question117.htm

That article might drive the EEs here a little batty.
AC doesn't actually flow. The electrons jiggle.
I checked a few pages down and found another obvious error.
There is another mistake he http://tinyurl.com/4dv2hch
just above the watt hour meter.

What, the step-down transformer? What's wrong with that?

And I have to disagree with you; who says AC doesn't flow? During the
positive half-cycle, current flows (electrons from negative to positive,
or "conventional current flow" in the opposite direction).

I have no idea where I read that thing about electrons just jiggling
in an AC circuit. Curiosity got the best of me so I snooped a bit.
These popped up: http://tinyurl.com/4pgadee
http://tinyurl.com/4ct2pqu

I suppose this explanation falls apart if looked at from the POV of
quantum physics, but for an explanation of current flow from an
electrical standpoint it's perfectly valid.

On Sat, 15 Jan 2011 08:10:53 -0500, Jeff Thies wrote:

On 1/13/2011 4:36 PM, David Nebenzahl wrote:
On 1/12/2011 7:22 PM Ralph Mowery spake thus:

"Dean Hoffman" wrote in message
...

Metspitzer wrote:

It is considered single phase. If you remove the center tap, you
have the same thing on the primary as you do on the secondary.

If you chose to put the secondary tap anywhere but the center,
you still have 240 total, but the fraction of 240 changes as you
move the center tap.

This sentence is the one that doesn't ring true. "The two insulated
wires each carry 120 volts, but they are 180 degrees out of phase
so the difference between them is 240 volts. "

The common 240 volt system in the US is only single phase. A true 2
phase system will have the the voltages only 90 deg out of phase. In a
240 volt single phase system , the center, neutral or whatever you
want to call the wire will carry only the unballanced currents and can
be the same size as the other two wires. A true 2 phase system usually
has 4 wires, but it it is wired up with only 3 wires, the 'center'
wire has to be the largest wire.

There are always some on here that do not understand the differance in
a split phase 120/240 volts system ususally used in the homes and a
true 2 phase system. I doubt that hardly anyone here has seem a true 2
phase power system.

No, I had never really known what they were until now. Just looked it
up, and it's just as you say.

I'm wondering, though, just how effective or even useful 2-phase systems
really were. If you graph the waveforms, you see that there's a hole in
it, a "missing" phase, the one that would start at 180° that's present
in a 3-phase system. So what you have is current pulses that go
"bump-bump (pause)" instead of "bump-bump-bump", right?

Apparently that's one reason that 3-phase superseded 2-phase power. It's
true that 2-phase was better than single-phase for running certain types
of induction motors.

In particular starting torque. All motors need a push in the right
direction to get them going. Often this is an artificial phase made by
the starting cap. You really want 3 phase for the big motors. In fact
the power company generates 3 phase power (sort of the reverse of a
synchronous motor), barring electronic means it is hard to get otherwise.

Not hard to get. A rotary phase converter will do it. Many woodworkers use a
three-phase induction motor as a rotary phase converter to power big tools
(often bought at auction from commercial installations).

It's a matter of semantics, I know, but the 120+120=240 system we've
been discussing actually is a 2-phase system, even though it's not
really called that. One side is 180° out of phase with the other side,
so by definition you have a 2-phase system.

Technically, it's not two phase at all.

Jeff Thies wrote:
On 1/13/2011 4:36 PM, David Nebenzahl wrote:
On 1/12/2011 7:22 PM Ralph Mowery spake thus:

"Dean Hoffman" wrote in message
...

Metspitzer wrote:

It is considered single phase. If you remove the center tap, you
have the same thing on the primary as you do on the secondary.

If you chose to put the secondary tap anywhere but the center,
you still have 240 total, but the fraction of 240 changes as you
move the center tap.

This sentence is the one that doesn't ring true. "The two insulated
wires each carry 120 volts, but they are 180 degrees out of phase
so the difference between them is 240 volts. "

The common 240 volt system in the US is only single phase. A true 2
phase system will have the the voltages only 90 deg out of phase. In a
240 volt single phase system , the center, neutral or whatever you
want to call the wire will carry only the unballanced currents and can
be the same size as the other two wires. A true 2 phase system usually
has 4 wires, but it it is wired up with only 3 wires, the 'center'
wire has to be the largest wire.

There are always some on here that do not understand the differance in
a split phase 120/240 volts system ususally used in the homes and a
true 2 phase system. I doubt that hardly anyone here has seem a true 2
phase power system.

I haven't seen one.
(Weren't the original Westinghouse/Tesla AC generators at Niagara falls
2-phase?)

I have seen Scott (or T connected) small 3 phase transformers that
essentially convert 3-phase to 2-phase to 3-phase (2 transformers for
480/277 to 308/277).


No, I had never really known what they were until now. Just looked it
up, and it's just as you say.

I'm wondering, though, just how effective or even useful 2-phase systems
really were. If you graph the waveforms, you see that there's a hole in
it, a "missing" phase, the one that would start at 180° that's present
in a 3-phase system. So what you have is current pulses that go
"bump-bump (pause)" instead of "bump-bump-bump", right?

Apparently that's one reason that 3-phase superseded 2-phase power. It's
true that 2-phase was better than single-phase for running certain types
of induction motors.

Three phase probably uses significantly less copper to convey a given
amount of power.


In particular starting torque. All motors need a push in the right
direction to get them going. Often this is an artificial phase made by
the starting cap. You really want 3 phase for the big motors. In fact
the power company generates 3 phase power (sort of the reverse of a
synchronous motor), barring electronic means it is hard to get otherwise.


Three phase motors are probably cheaper than single phase starting at
somewhere less than 1 HP.


It's a matter of semantics, I know, but the 120+120=240 system we've
been discussing actually is a 2-phase system, even though it's not
really called that. One side is 180° out of phase with the other side,
so by definition you have a 2-phase system.

It is indeed. The main advantage here is that you can combine the phases
to get a higher voltage. Less current. A 120V dryer would take some
hefty wiring.

You combine a 120V transformer winding with another 120V transformer
winding that is in-phase to get 240V. In fact, as everyone knows, it is
a single winding with a center tap.

You won't find an electrical engineer for power systems who will say
120/240V is not single phase. You are not likely to find an electrician
that deals with 3-phase who says 120/240V is not single phase. Wikipedia
is not likely to say 120/240 is 2-phase.

--
bud--

On Sat, 15 Jan 2011 10:48:33 -0600, bud-- wrote:

Jeff Thies wrote:
On 1/13/2011 4:36 PM, David Nebenzahl wrote:
On 1/12/2011 7:22 PM Ralph Mowery spake thus:

"Dean Hoffman" wrote in message
...

Metspitzer wrote:

It is considered single phase. If you remove the center tap, you
have the same thing on the primary as you do on the secondary.

If you chose to put the secondary tap anywhere but the center,
you still have 240 total, but the fraction of 240 changes as you
move the center tap.

This sentence is the one that doesn't ring true. "The two insulated
wires each carry 120 volts, but they are 180 degrees out of phase
so the difference between them is 240 volts. "

The common 240 volt system in the US is only single phase. A true 2
phase system will have the the voltages only 90 deg out of phase. In a
240 volt single phase system , the center, neutral or whatever you
want to call the wire will carry only the unballanced currents and can
be the same size as the other two wires. A true 2 phase system usually
has 4 wires, but it it is wired up with only 3 wires, the 'center'
wire has to be the largest wire.

There are always some on here that do not understand the differance in
a split phase 120/240 volts system ususally used in the homes and a
true 2 phase system. I doubt that hardly anyone here has seem a true 2
phase power system.

I haven't seen one.
(Weren't the original Westinghouse/Tesla AC generators at Niagara falls
2-phase?)

I have seen Scott (or T connected) small 3 phase transformers that
essentially convert 3-phase to 2-phase to 3-phase (2 transformers for
480/277 to 308/277).

A Scott-T needs two phases to get a third. One split phase won't do it.

No, I had never really known what they were until now. Just looked it
up, and it's just as you say.

I'm wondering, though, just how effective or even useful 2-phase systems
really were. If you graph the waveforms, you see that there's a hole in
it, a "missing" phase, the one that would start at 180° that's present
in a 3-phase system. So what you have is current pulses that go
"bump-bump (pause)" instead of "bump-bump-bump", right?

Apparently that's one reason that 3-phase superseded 2-phase power. It's
true that 2-phase was better than single-phase for running certain types
of induction motors.

Three phase probably uses significantly less copper to convey a given
amount of power.

Yes. Increased efficiency, too.

In particular starting torque. All motors need a push in the right
direction to get them going. Often this is an artificial phase made by
the starting cap. You really want 3 phase for the big motors. In fact
the power company generates 3 phase power (sort of the reverse of a
synchronous motor), barring electronic means it is hard to get otherwise.


Three phase motors are probably cheaper than single phase starting at
somewhere less than 1 HP.

Simpler, but I doubt cheaper (volume).

It's a matter of semantics, I know, but the 120+120=240 system we've
been discussing actually is a 2-phase system, even though it's not
really called that. One side is 180° out of phase with the other side,
so by definition you have a 2-phase system.

It is indeed. The main advantage here is that you can combine the phases
to get a higher voltage. Less current. A 120V dryer would take some
hefty wiring.

You combine a 120V transformer winding with another 120V transformer
winding that is in-phase to get 240V. In fact, as everyone knows, it is
a single winding with a center tap.

You won't find an electrical engineer for power systems who will say
120/240V is not single phase. You are not likely to find an electrician
that deals with 3-phase who says 120/240V is not single phase. Wikipedia
is not likely to say 120/240 is 2-phase.

Only because it's not. ;-)

On 1/15/2011 11:22 AM, zzzzzzzzzz wrote:
On Sat, 15 Jan 2011 08:10:53 -0500, Jeff wrote:

On 1/13/2011 4:36 PM, David Nebenzahl wrote:
On 1/12/2011 7:22 PM Ralph Mowery spake thus:

"Dean wrote in message
...

Metspitzer wrote:

It is considered single phase. If you remove the center tap, you
have the same thing on the primary as you do on the secondary.

If you chose to put the secondary tap anywhere but the center,
you still have 240 total, but the fraction of 240 changes as you
move the center tap.

This sentence is the one that doesn't ring true. "The two insulated
wires each carry 120 volts, but they are 180 degrees out of phase
so the difference between them is 240 volts. "

The common 240 volt system in the US is only single phase. A true 2
phase system will have the the voltages only 90 deg out of phase. In a
240 volt single phase system , the center, neutral or whatever you
want to call the wire will carry only the unballanced currents and can
be the same size as the other two wires. A true 2 phase system usually
has 4 wires, but it it is wired up with only 3 wires, the 'center'
wire has to be the largest wire.

There are always some on here that do not understand the differance in
a split phase 120/240 volts system ususally used in the homes and a
true 2 phase system. I doubt that hardly anyone here has seem a true 2
phase power system.

No, I had never really known what they were until now. Just looked it
up, and it's just as you say.

I'm wondering, though, just how effective or even useful 2-phase systems
really were. If you graph the waveforms, you see that there's a hole in
it, a "missing" phase, the one that would start at 180° that's present
in a 3-phase system. So what you have is current pulses that go
"bump-bump (pause)" instead of "bump-bump-bump", right?

Apparently that's one reason that 3-phase superseded 2-phase power. It's
true that 2-phase was better than single-phase for running certain types
of induction motors.

In particular starting torque. All motors need a push in the right
direction to get them going. Often this is an artificial phase made by
the starting cap. You really want 3 phase for the big motors. In fact
the power company generates 3 phase power (sort of the reverse of a
synchronous motor), barring electronic means it is hard to get otherwise.

Not hard to get. A rotary phase converter will do it. Many woodworkers use a
three-phase induction motor as a rotary phase converter to power big tools
(often bought at auction from commercial installations).


I hadn't seen those before, using just a 3 phase idler motor. The Rotary
Phase Converters I had see were more traditional, and more involved
pieces of machinery (not to mention expensive). But it is not necessary
for a woodworking motor to have perfectly balanced 3 phase. Clever and
useful, nonetheless.

HVDC doesn't seem to have much impact in the US, but my rough
understanding is that converting back is all solid state these days.


It's a matter of semantics, I know, but the 120+120=240 system we've
been discussing actually is a 2-phase system, even though it's not
really called that. One side is 180° out of phase with the other side,
so by definition you have a 2-phase system.

Technically, it's not two phase at all.

Call it what you want, but the two 120V lines are 180 out of phase
relative to neutral. Certainly not useful for starting a motor. I'll not
quibble over symantics.

Jeff

On Sat, 15 Jan 2011 13:04:40 -0500, Jeff Thies wrote:

On 1/15/2011 11:22 AM, zzzzzzzzzz wrote:
On Sat, 15 Jan 2011 08:10:53 -0500, Jeff wrote:

On 1/13/2011 4:36 PM, David Nebenzahl wrote:
On 1/12/2011 7:22 PM Ralph Mowery spake thus:

"Dean wrote in message
...

Metspitzer wrote:

It is considered single phase. If you remove the center tap, you
have the same thing on the primary as you do on the secondary.

If you chose to put the secondary tap anywhere but the center,
you still have 240 total, but the fraction of 240 changes as you
move the center tap.

This sentence is the one that doesn't ring true. "The two insulated
wires each carry 120 volts, but they are 180 degrees out of phase
so the difference between them is 240 volts. "

The common 240 volt system in the US is only single phase. A true 2
phase system will have the the voltages only 90 deg out of phase. In a
240 volt single phase system , the center, neutral or whatever you
want to call the wire will carry only the unballanced currents and can
be the same size as the other two wires. A true 2 phase system usually
has 4 wires, but it it is wired up with only 3 wires, the 'center'
wire has to be the largest wire.

There are always some on here that do not understand the differance in
a split phase 120/240 volts system ususally used in the homes and a
true 2 phase system. I doubt that hardly anyone here has seem a true 2
phase power system.

No, I had never really known what they were until now. Just looked it
up, and it's just as you say.

I'm wondering, though, just how effective or even useful 2-phase systems
really were. If you graph the waveforms, you see that there's a hole in
it, a "missing" phase, the one that would start at 180° that's present
in a 3-phase system. So what you have is current pulses that go
"bump-bump (pause)" instead of "bump-bump-bump", right?

Apparently that's one reason that 3-phase superseded 2-phase power. It's
true that 2-phase was better than single-phase for running certain types
of induction motors.

In particular starting torque. All motors need a push in the right
direction to get them going. Often this is an artificial phase made by
the starting cap. You really want 3 phase for the big motors. In fact
the power company generates 3 phase power (sort of the reverse of a
synchronous motor), barring electronic means it is hard to get otherwise.

Not hard to get. A rotary phase converter will do it. Many woodworkers use a
three-phase induction motor as a rotary phase converter to power big tools
(often bought at auction from commercial installations).


I hadn't seen those before, using just a 3 phase idler motor. The Rotary
Phase Converters I had see were more traditional, and more involved
pieces of machinery (not to mention expensive). But it is not necessary
for a woodworking motor to have perfectly balanced 3 phase. Clever and
useful, nonetheless.

HVDC doesn't seem to have much impact in the US, but my rough
understanding is that converting back is all solid state these days.


It's a matter of semantics, I know, but the 120+120=240 system we've
been discussing actually is a 2-phase system, even though it's not
really called that. One side is 180° out of phase with the other side,
so by definition you have a 2-phase system.

Technically, it's not two phase at all.

Call it what you want, but the two 120V lines are 180 out of phase
relative to neutral. Certainly not useful for starting a motor. I'll not
quibble over symantics.

No they, in fact, aren't. One is the negative of the other.

zzzzzzzzzz wrote:
....

No they, in fact, aren't. One is the negative of the other.

Which is the same as a time phase shift of pi radians.

To see so (in Matlab)

t=[0:2*pi/100:2*pi];
v=sin(t);
plot(t,v,t,-v)
hold on
plot(t2,v,'rx')


The resulting plot is a complete sine wave over 0-2pi, the negative of
that and the last (while starting at -pi) overlays the -v section from
0-pi identically (and will from there on out if extended the t2 axis.

There are two meanings of "phase" here which is the difficulty in common
usage. The generation is indeed a single electrical phase; the two
derived currents are out of phase (in time) with each other.

--

On Sat, 15 Jan 2011 12:45:26 -0600, dpb wrote:

wrote:
...

No they, in fact, aren't. One is the negative of the other.

Which is the same as a time phase shift of pi radians.

To see so (in Matlab)

Matlab is wrong.

t=[0:2*pi/100:2*pi];
v=sin(t);
plot(t,v,t,-v)
hold on
plot(t2,v,'rx')


The resulting plot is a complete sine wave over 0-2pi, the negative of
that and the last (while starting at -pi) overlays the -v section from
0-pi identically (and will from there on out if extended the t2 axis.

There are two meanings of "phase" here which is the difficulty in common
usage. The generation is indeed a single electrical phase; the two
derived currents are out of phase (in time) with each other.

zzzzzzzzzz wrote:
On Sat, 15 Jan 2011 12:45:26 -0600, dpb wrote:

zzzzzzzzzz wrote:
...

No they, in fact, aren't. One is the negative of the other.
Which is the same as a time phase shift of pi radians.

To see so (in Matlab)

Matlab is wrong.
....

Not unless

sin(pi–t) = sin t

cos(pi–t) = –cos t

are no longer identities...

--

dpb wrote:
zzzzzzzzzz wrote:
...

No they, in fact, aren't. One is the negative of the other.

Which is the same as a time phase shift of pi radians.

To see so (in Matlab)

t=[0:2*pi/100:2*pi];
v=sin(t);
plot(t,v,t,-v)
hold on

t2=t-pi;

plot(t2,v,'rx')


Above is missing one line that somehow didn't get pasted from the Matlab
command window...the definition of t2--see above

The resulting plot is a complete sine wave over 0-2pi, the negative of
that and the last (while starting at -pi) overlays the -v section from
0-pi identically (and will from there on out if extended the t2 axis.

There are two meanings of "phase" here which is the difficulty in common
usage. The generation is indeed a single electrical phase; the two
derived currents are out of phase (in time) with each other.

--

On Sat, 15 Jan 2011 14:03:45 -0600, dpb wrote:

wrote:
On Sat, 15 Jan 2011 12:45:26 -0600, dpb wrote:

zzzzzzzzzz wrote:
...

No they, in fact, aren't. One is the negative of the other.
Which is the same as a time phase shift of pi radians.

To see so (in Matlab)

Matlab is wrong.
...

Not unless

sin(pi–t) = sin t

cos(pi–t) = –cos t

are no longer identities...

Ok, your understanding of what Matlab is telling you is wrong.

zzzzzzzzzz wrote:
On Sat, 15 Jan 2011 14:03:45 -0600, dpb wrote:

zzzzzzzzzz wrote:
On Sat, 15 Jan 2011 12:45:26 -0600, dpb wrote:

zzzzzzzzzz wrote:
...

No they, in fact, aren't. One is the negative of the other.
Which is the same as a time phase shift of pi radians.

To see so (in Matlab)
Matlab is wrong.
...

Not unless

sin(pi–t) = sin t

cos(pi–t) = –cos t

are no longer identities...

Ok, your understanding of what Matlab is telling you is wrong.

How thinketh thou so? That's what's happening in the transformer by the
location of the two taps -- taking the voltage at two differing points
along the (single) sinusoidal waveform at the same point in time is the
same thing as a phase shift of one relative to the other.

Again, as noted above it's the confusion between the two meanings of
"phase" -- the (single) electrical generation phase and the phase shift
along that sinusoidal waveform for the two individual voltages.

--

On Sat, 15 Jan 2011 14:25:54 -0600, dpb wrote:

wrote:
On Sat, 15 Jan 2011 14:03:45 -0600, dpb wrote:

zzzzzzzzzz wrote:
On Sat, 15 Jan 2011 12:45:26 -0600, dpb wrote:

zzzzzzzzzz wrote:
...

No they, in fact, aren't. One is the negative of the other.
Which is the same as a time phase shift of pi radians.

To see so (in Matlab)
Matlab is wrong.
...

Not unless

sin(pi–t) = sin t

cos(pi–t) = –cos t

are no longer identities...

Ok, your understanding of what Matlab is telling you is wrong.

How thinketh thou so?

Math engineering

That's what's happening in the transformer by the
location of the two taps -- taking the voltage at two differing points
along the (single) sinusoidal waveform at the same point in time is the
same thing as a phase shift of one relative to the other.

Nope. Define CT as zero. The signals at each end are the same but opposite
sign.

Again, as noted above it's the confusion between the two meanings of
"phase" -- the (single) electrical generation phase and the phase shift
along that sinusoidal waveform for the two individual voltages.

THen why are you using Matlab as your source?

On 1/15/2011 3:25 PM, dpb wrote:
zzzzzzzzzz wrote:
On Sat, 15 Jan 2011 14:03:45 -0600, dpb wrote:

zzzzzzzzzz wrote:
On Sat, 15 Jan 2011 12:45:26 -0600, dpb wrote:

zzzzzzzzzz wrote:
...

No they, in fact, aren't. One is the negative of the other.
Which is the same as a time phase shift of pi radians.

To see so (in Matlab)
Matlab is wrong.
...

Not unless

sin(pi–t) = sin t

I think you mean: - sin t

cos(pi–t) = –cos t

are no longer identities...

Ok, your understanding of what Matlab is telling you is wrong.

How thinketh thou so? That's what's happening in the transformer by the
location of the two taps -- taking the voltage at two differing points
along the (single) sinusoidal waveform at the same point in time is the
same thing as a phase shift of one relative to the other.

Again, as noted above it's the confusion between the two meanings of
"phase" -- the (single) electrical generation phase and the phase shift
along that sinusoidal waveform for the two individual voltages.

That completely sums it up for me. And better put than I could. :-)

Jeff

--

That like blueberry pi?

--
Christopher A. Young
Learn more about Jesus
www.lds.org
..


"dpb" wrote in message
...
zzzzzzzzzz wrote:
....

No they, in fact, aren't. One is the negative of the
other.

Which is the same as a time phase shift of pi radians.

To see so (in Matlab)

On 1/15/2011 6:37 AM Dean Hoffman spake thus:

David Nebenzahl wrote:

On 1/12/2011 5:16 PM Dean Hoffman spake thus:

Frank wrote:

http://home.howstuffworks.com/question117.htm

That article might drive the EEs here a little batty. AC doesn't
actually flow. The electrons jiggle.

And I have to disagree with you; who says AC doesn't flow? During the
positive half-cycle, current flows (electrons from negative to positive,
or "conventional current flow" in the opposite direction).

I have no idea where I read that thing about electrons just jiggling
in an AC circuit. Curiosity got the best of me so I snooped a bit.
These popped up: http://tinyurl.com/4pgadee
http://tinyurl.com/4ct2pqu

OK, that's interesting; thanks. I'd never read that explanation. (I'd
sooner trust the BPA article than that online forum that seems to have a
lot of clueless, unscientific types posting to it.)

So what they're saying is that, basically, even though electricity moves
at [about] the speed of light, electrons actually move very slowly.
Verrrrrry slowly.

But that doesn't change the fact that in both DC and AC, *current*
flows, almost instantaneously in both cases. It's just that current
doesn't necessarily coincide with electron motion.

(I have no idea now how electron and current flow actually works, but
again, that's at the quantum physics level. Us boneheaded electricians
can still go on thinking that AC currents flow, not "jiggle".)


--
Comment on quaint Usenet customs, from Usenet:

To me, the *plonk...* reminds me of the old man at the public hearing
who stands to make his point, then removes his hearing aid as a sign
that he is not going to hear any rebuttals.

Present!!

--
Christopher A. Young
Learn more about Jesus
www.lds.org
..


"David Nebenzahl"
wrote in message
.com...

OK, that's interesting; thanks. I'd never read that
explanation. (I'd sooner trust the BPA article than
that online forum that seems to have a lot of
clueless, unscientific types posting to it.)

On 1/15/2011 2:33 PM Stormin Mormon spake thus:

Present!!

We know, we know. You no longer have to prove to us that you're an idiot.


--
Comment on quaint Usenet customs, from Usenet:

To me, the *plonk...* reminds me of the old man at the public hearing
who stands to make his point, then removes his hearing aid as a sign
that he is not going to hear any rebuttals.

zzzzzzzzzz wrote:
....


Nope. Define CT as zero. The signals at each end are the same but opposite
sign.

Of course, because one "leads" the other by pi radians...

Again, as noted above it's the confusion between the two meanings of
"phase" -- the (single) electrical generation phase and the phase shift
along that sinusoidal waveform for the two individual voltages.

THen why are you using Matlab as your source?

Not "source", simply a demonstration of how the phase shift leads to the
apparent negation of a sine wave.

--

zzzzzzzzzz wrote:
....

How thinketh thou so?

Math engineering
....

I didn't see the above mind-boggler earlier...

It (application of math) is pretty much the definition of engineering...

--

On Sat, 15 Jan 2011 16:48:26 -0600, dpb wrote:

wrote:
...


Nope. Define CT as zero. The signals at each end are the same but opposite
sign.

Of course, because one "leads" the other by pi radians...

Wrong, obviously.

Again, as noted above it's the confusion between the two meanings of
"phase" -- the (single) electrical generation phase and the phase shift
along that sinusoidal waveform for the two individual voltages.

THen why are you using Matlab as your source?

Not "source", simply a demonstration of how the phase shift leads to the
apparent negation of a sine wave.

Complete bull****.

On Sat, 15 Jan 2011 17:03:24 -0600, dpb wrote:

wrote:
...

How thinketh thou so?

Math engineering
...

I didn't see the above mind-boggler earlier...

It (application of math) is pretty much the definition of engineering...

What a bull****ter.

Fishhook. Mouth. Remove. Better, now, dear?

--
Christopher A. Young
Learn more about Jesus
www.lds.org
..


"David Nebenzahl" wrote in message
.com...
On 1/15/2011 2:33 PM Stormin Mormon spake thus:

Present!!

We know, we know. You no longer have to prove to us that
you're an idiot.


--
Comment on quaint Usenet customs, from Usenet:

To me, the *plonk...* reminds me of the old man at the
public hearing
who stands to make his point, then removes his hearing
aid as a sign
that he is not going to hear any rebuttals.

On 1/15/2011 6:30 PM, zzzzzzzzzz wrote:
On Sat, 15 Jan 2011 17:03:24 -0600, wrote:

zzzzzzzzzz wrote:
...

How thinketh thou so?

Math engineering
...

I didn't see the above mind-boggler earlier...

It (application of math) is pretty much the definition of engineering...

What a bull****ter.


Do you have a degree in engineering? Most of the courses are math.
Been there, done that.

A 180 degree (pi radians, one half circle) out of phase sine wave is
identical to an inverted sine wave. One half cycle is by *definition*
180 degrees. The math, if you had any regard for it, is very simple.

If you want to throw out science and math, then we really have
nothing further to discuss here.

Jeff

On Sun, 16 Jan 2011 09:27:59 -0500, Jeff Thies wrote:

On 1/15/2011 6:30 PM, zzzzzzzzzz wrote:
On Sat, 15 Jan 2011 17:03:24 -0600, wrote:

zzzzzzzzzz wrote:
...

How thinketh thou so?

Math engineering
...

I didn't see the above mind-boggler earlier...

It (application of math) is pretty much the definition of engineering...

What a bull****ter.


Do you have a degree in engineering? Most of the courses are math.
Been there, done that.

Yes. ...and 37 years experience as a design engineer.

A 180 degree (pi radians, one half circle) out of phase sine wave is
identical to an inverted sine wave. One half cycle is by *definition*
180 degrees. The math, if you had any regard for it, is very simple.

That's not the point. It is *ONE* phase that has been split in two by a
transformer's center tap. It is properly called "split-phase". Two-phase is
something entirely different, which if you didn't get your "degree" from a
Cracker Jax box, you'd know.

If you want to throw out science and math, then we really have
nothing further to discuss here.

You generally don't.