Aww, you sprung my trap!

The previous poster was expostulating on running the motor on 3, 2 and 1
phase. I was waiting for him to show me the difference between the 2 phase
and single phase connections!

Same basic concept as phase rotation in a 3 phase system. You and I think
there are only two, but there are really many; ABC, BAC, CBA, ACB etc.etc.

(Facetious mode turned OFF)

I spent many years in an old manufacturing city in the Northeast, where we
had, in common use on a daily basis, AC (25 and 60 Hz), DC, every possible
permutation of 3 phase, 2 phase 3,4 and 5 wire, and everything in between.
My absolute favorite was the 6 phase double delta. Picture a straight 220
(YES, 220, not 240) delta connection. Now, center tap all the transformers,
and these midpoints give you another delta at 110 for the lighting load. Of
course, the whole thing is ungrounded. Yes, all the light switches in the
building were 2 pole. Yes, the small motors were 110 volt 3 phase. This
system gives you 2 three-phase voltages out of one set of transformers, The
power factor transforms at unity, unlike many connections. Only thing is, it
is very had to protect the transformers unless you use 6 primary fuses.

Years ago, maintenance electricians had to be aware of a lot of varied
systems. Today, life is a whole lot simpler.

Thanks in advance.

"Spehro Pefhany" wrote in message
news
On Sat, 3 Jan 2004 09:30:19 -0500, the renowned "BFoelsch"
wrote:

How would you hook up a 3-phase motor to run on 2 phases?

A 3-phase motor has 3 wires. If you break one wire, it's running on
single phase, not two. Break two wires and it tends to just sit there.

How would you hook up a 3 phase motor to run on one phase?

I don't care whether they work or not, I just want to see the wiring
diagram.

Single phase applied to two of the three wires. It works better with
capacitors to the third (otherwise unconnected) wire. The motor won't
start like this, you either need to give it a spin or use another
(starting) capacitor and some switching.


Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
Info for manufacturers:
http://www.trexon.com
Embedded software/hardware/analog Info for designers:
http://www.speff.com

Aww, you sprung my trap!

The previous poster was expostulating on running the motor on 3, 2 and 1
phase. I was waiting for him to show me the difference between the 2 phase
and single phase connections!

Same basic concept as phase rotation in a 3 phase system. You and I think
there are only two, but there are really many; ABC, BAC, CBA, ACB etc.etc.

(Facetious mode turned OFF)

I spent many years in an old manufacturing city in the Northeast, where we
had, in common use on a daily basis, AC (25 and 60 Hz), DC, every possible
permutation of 3 phase, 2 phase 3,4 and 5 wire, and everything in between.
My absolute favorite was the 6 phase double delta. Picture a straight 220
(YES, 220, not 240) delta connection. Now, center tap all the transformers,
and these midpoints give you another delta at 110 for the lighting load. Of
course, the whole thing is ungrounded. Yes, all the light switches in the
building were 2 pole. Yes, the small motors were 110 volt 3 phase. This
system gives you 2 three-phase voltages out of one set of transformers, The
power factor transforms at unity, unlike many connections. Only thing is, it
is very had to protect the transformers unless you use 6 primary fuses.

Years ago, maintenance electricians had to be aware of a lot of varied
systems. Today, life is a whole lot simpler.

Thanks in advance.

"Spehro Pefhany" wrote in message
news
On Sat, 3 Jan 2004 09:30:19 -0500, the renowned "BFoelsch"
wrote:

How would you hook up a 3-phase motor to run on 2 phases?

A 3-phase motor has 3 wires. If you break one wire, it's running on
single phase, not two. Break two wires and it tends to just sit there.

How would you hook up a 3 phase motor to run on one phase?

I don't care whether they work or not, I just want to see the wiring
diagram.

Single phase applied to two of the three wires. It works better with
capacitors to the third (otherwise unconnected) wire. The motor won't
start like this, you either need to give it a spin or use another
(starting) capacitor and some switching.


Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
Info for manufacturers:
http://www.trexon.com
Embedded software/hardware/analog Info for designers:
http://www.speff.com

In sci.electronics.basics Spehro Pefhany wrote:
| On Sat, 3 Jan 2004 09:30:19 -0500, the renowned "BFoelsch"
| wrote:
|
|How would you hook up a 3-phase motor to run on 2 phases?
|
| A 3-phase motor has 3 wires. If you break one wire, it's running on
| single phase, not two. Break two wires and it tends to just sit there.

2 phase would not be the result of a failure of power source, but it could
happen if the internal windings/circuit on one of the phases opened up.
I've never seen that happen but I can't say it's impossible.

--
-----------------------------------------------------------------------------
| Phil Howard KA9WGN | http://linuxhomepage.com/ http://ham.org/ |
| (first name) at ipal.net | http://phil.ipal.org/ http://ka9wgn.ham.org/ |
-----------------------------------------------------------------------------

In sci.electronics.basics Spehro Pefhany wrote:
| On Sat, 3 Jan 2004 09:30:19 -0500, the renowned "BFoelsch"
| wrote:
|
|How would you hook up a 3-phase motor to run on 2 phases?
|
| A 3-phase motor has 3 wires. If you break one wire, it's running on
| single phase, not two. Break two wires and it tends to just sit there.

2 phase would not be the result of a failure of power source, but it could
happen if the internal windings/circuit on one of the phases opened up.
I've never seen that happen but I can't say it's impossible.

--
-----------------------------------------------------------------------------
| Phil Howard KA9WGN | http://linuxhomepage.com/ http://ham.org/ |
| (first name) at ipal.net | http://phil.ipal.org/ http://ka9wgn.ham.org/ |
-----------------------------------------------------------------------------

On Sat, 3 Jan 2004 09:30:19 -0500, the renowned "BFoelsch"
wrote:

How would you hook up a 3-phase motor to run on 2 phases?

A 3-phase motor has 3 wires. If you break one wire, it's running on
single phase, not two. Break two wires and it tends to just sit there.

How would you hook up a 3 phase motor to run on one phase?

I don't care whether they work or not, I just want to see the wiring
diagram.

Single phase applied to two of the three wires. It works better with
capacitors to the third (otherwise unconnected) wire. The motor won't
start like this, you either need to give it a spin or use another
(starting) capacitor and some switching.


Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com

How would you hook up a 3-phase motor to run on 2 phases?

How would you hook up a 3 phase motor to run on one phase?

I don't care whether they work or not, I just want to see the wiring
diagram.

Thanks in advance.

"Rob Paisley" wrote in message
om...
Bill wrote in message
...
wrote:

In sci.electronics.basics Rob Paisley wrote:

| For larger horsepower motors, Three Phases means that they will
| start with no external mechanical assistance.

And, as I understand it, they can then "stand on one leg" although
they
will be a bit "shaky".

You can also reverse the rotation by swapping two of the phases. If one
phase is blown you can start it by giving it a spin in the right
direction, 'without' getting your hand caught

Bill Baka

I am not sure if a 3 phase motor would even rotate unloaded on 2
phases but it certainly would not develop a usable amount of
horsepower. I would suspect that running on 1 phase would be out of
the question.

I do know that if a loaded 3 phase motor blows a fuse it will almost
always blow a fuse in one of the other lines due to an overload. Due
to the way the control power for the motor is connected the starter
will then open the circuit if it did not already do so when the first
fuse failed.

Also, there is a number of 1.57 being bandied about in this thread
for the relative horse power of a 3 phase versus single motor for a
given current. This number should be 1.73 (The square root of 3.

Rob.

Rob Paisley wrote:
Bill wrote in message ...

wrote:


In sci.electronics.basics Rob Paisley wrote:

| For larger horsepower motors, Three Phases means that they will
| start with no external mechanical assistance.

And, as I understand it, they can then "stand on one leg" although they
will be a bit "shaky".


You can also reverse the rotation by swapping two of the phases. If one
phase is blown you can start it by giving it a spin in the right
direction, 'without' getting your hand caught

Bill Baka


I am not sure if a 3 phase motor would even rotate unloaded on 2
phases but it certainly would not develop a usable amount of
horsepower. I would suspect that running on 1 phase would be out of
the question.

I do know that if a loaded 3 phase motor blows a fuse it will almost
always blow a fuse in one of the other lines due to an overload. Due
to the way the control power for the motor is connected the starter
will then open the circuit if it did not already do so when the first
fuse failed.

Also, there is a number of 1.57 being bandied about in this thread
for the relative horse power of a 3 phase versus single motor for a
given current. This number should be 1.73 (The square root of 3.

Rob.
The motor I replaced was on an air conditioning blower and would rotate
if given a boost before turning on the power, but as you said not with
enough power. It just would not start without the third phase. The fix
was to replace a 3/4 horse motor with a 1 horse motor in the same NEMA
frame size. It was a 480 volt unit so we did not play much with it and
just tossed it. Seems us engineer types prefer 5 volt stuff.
Bill Baka

Rob Paisley wrote:
Bill wrote in message ...

wrote:


In sci.electronics.basics Rob Paisley wrote:

| For larger horsepower motors, Three Phases means that they will
| start with no external mechanical assistance.

And, as I understand it, they can then "stand on one leg" although they
will be a bit "shaky".


You can also reverse the rotation by swapping two of the phases. If one
phase is blown you can start it by giving it a spin in the right
direction, 'without' getting your hand caught

Bill Baka


I am not sure if a 3 phase motor would even rotate unloaded on 2
phases but it certainly would not develop a usable amount of
horsepower. I would suspect that running on 1 phase would be out of
the question.

I do know that if a loaded 3 phase motor blows a fuse it will almost
always blow a fuse in one of the other lines due to an overload. Due
to the way the control power for the motor is connected the starter
will then open the circuit if it did not already do so when the first
fuse failed.

Also, there is a number of 1.57 being bandied about in this thread
for the relative horse power of a 3 phase versus single motor for a
given current. This number should be 1.73 (The square root of 3.

Rob.
The motor I replaced was on an air conditioning blower and would rotate
if given a boost before turning on the power, but as you said not with
enough power. It just would not start without the third phase. The fix
was to replace a 3/4 horse motor with a 1 horse motor in the same NEMA
frame size. It was a 480 volt unit so we did not play much with it and
just tossed it. Seems us engineer types prefer 5 volt stuff.
Bill Baka

Why is three phase used?
Several people mentined the reason (motors) , but didn't go further. To
get a motor to turn you have to generate a magnetic field that "turns".
With three phase this can be done. The relative voltage/cirrent between two
phases (lines) can each drive a winding and the result is a rotating
magnetic field inside the motor. This will then "drag" the rotor around.
With the single phase motor, this rotation must be made some other way.
With the capacitor start/run motors, the cap provides some phase shift on a
second winding giving a pseudo two phase supply and therefore some rotation
in the field. The cap-start motors do then run on one phase when the cap is
switched out. Thus the comments on "running a three phase motor on 2 phases
(actually this is just one phase when one of the three lines is cut -- the
"three phases" needed for the motor are not the three lines, but the phase
between each TWO line-pairs...of which there are three pairs) .
Shaded pole motors use a part of the field core which is separated from
the main core.. You will see a single turn of large copper wire wound
around a small section of the core. This "shorted turn" causes a lag in the
field in that section of the core and a resulting rotation of the composite
field. These are usually in small blowers like typically found in bathroom
fans. Go to the hardweare store and look at one of these motors.

Steve K;9;D:C:I
..

Why is three phase used?
Several people mentined the reason (motors) , but didn't go further. To
get a motor to turn you have to generate a magnetic field that "turns".
With three phase this can be done. The relative voltage/cirrent between two
phases (lines) can each drive a winding and the result is a rotating
magnetic field inside the motor. This will then "drag" the rotor around.
With the single phase motor, this rotation must be made some other way.
With the capacitor start/run motors, the cap provides some phase shift on a
second winding giving a pseudo two phase supply and therefore some rotation
in the field. The cap-start motors do then run on one phase when the cap is
switched out. Thus the comments on "running a three phase motor on 2 phases
(actually this is just one phase when one of the three lines is cut -- the
"three phases" needed for the motor are not the three lines, but the phase
between each TWO line-pairs...of which there are three pairs) .
Shaded pole motors use a part of the field core which is separated from
the main core.. You will see a single turn of large copper wire wound
around a small section of the core. This "shorted turn" causes a lag in the
field in that section of the core and a resulting rotation of the composite
field. These are usually in small blowers like typically found in bathroom
fans. Go to the hardweare store and look at one of these motors.

Steve K;9;D:C:I
..