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.

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.

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

Oops, should have said that this connection needed 6 SECONDARY fuses.

Sorry about that.

"BFoelsch" wrote in message
...
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

On Sat, 3 Jan 2004 10:34:35 -0500, "BFoelsch"
wrote:


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.


Wow. If it was delta, then 110 3-phase would require 6 wires (or five
if you cheat and share one corner) so the 110 3-phase motor would need
three isolated windings and most likely a 6-pole on/off switch. Was it
really like that? Might it have been wired wye with one central
common/neutral? That seems more logical, but then maybe it wasn't very
logical.

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

The thing that always amazes me is that buildings are wired in the
most bizarre ways, and no documentation is left behind. If you call in
an electrician, they figure it out somehow, kluge it some more, and
leave.

John

"John Larkin" wrote in
message ...
Wow. If it was delta, then 110 3-phase would require 6 wires (or five
if you cheat and share one corner) so the 110 3-phase motor would need
three isolated windings and most likely a 6-pole on/off switch. Was it
really like that?

Nope. Draw a picture of a Delta, center-tap each winding, and the three
center taps form another delta at half the voltage. Used a perfectly
standard (for 1922) 3 phase, 3 wire, 110v, 25Hz motor.

The 110 volt service made no connection to the corners of the 220 delta. The
110 delta was fed only from the center taps.

On Sat, 3 Jan 2004 14:10:54 -0500, "BFoelsch"
wrote:


"John Larkin" wrote in
message ...
Wow. If it was delta, then 110 3-phase would require 6 wires (or five
if you cheat and share one corner) so the 110 3-phase motor would need
three isolated windings and most likely a 6-pole on/off switch. Was it
really like that?

Nope. Draw a picture of a Delta, center-tap each winding, and the three
center taps form another delta at half the voltage. Used a perfectly
standard (for 1922) 3 phase, 3 wire, 110v, 25Hz motor.


Oh, yeah, OK. New Orleans is mostly below sea level, and the
Mississippi runs along most of it and peaks way above in the spring.
Up to fairly recently, New Orleans was drained by ancient pumps with
ancient switchgear, running on 25 Hz, and all the generators that made
the 25 Hz were (of course) in the city, below sea level too.

John

On Sat, 3 Jan 2004 14:10:54 -0500, "BFoelsch"
wrote:


"John Larkin" wrote in
message ...
Wow. If it was delta, then 110 3-phase would require 6 wires (or five
if you cheat and share one corner) so the 110 3-phase motor would need
three isolated windings and most likely a 6-pole on/off switch. Was it
really like that?

Nope. Draw a picture of a Delta, center-tap each winding, and the three
center taps form another delta at half the voltage. Used a perfectly
standard (for 1922) 3 phase, 3 wire, 110v, 25Hz motor.


Oh, yeah, OK. New Orleans is mostly below sea level, and the
Mississippi runs along most of it and peaks way above in the spring.
Up to fairly recently, New Orleans was drained by ancient pumps with
ancient switchgear, running on 25 Hz, and all the generators that made
the 25 Hz were (of course) in the city, below sea level too.

John

"John Larkin" wrote in
message ...
Wow. If it was delta, then 110 3-phase would require 6 wires (or five
if you cheat and share one corner) so the 110 3-phase motor would need
three isolated windings and most likely a 6-pole on/off switch. Was it
really like that?

Nope. Draw a picture of a Delta, center-tap each winding, and the three
center taps form another delta at half the voltage. Used a perfectly
standard (for 1922) 3 phase, 3 wire, 110v, 25Hz motor.

The 110 volt service made no connection to the corners of the 220 delta. The
110 delta was fed only from the center taps.