Is it possible to wire a 3 phase switch for two phase power?

TIA

Dan Miller
Seattle WA

Is it possible to wire a 3 phase switch for two phase power?

TIA

Dan Miller
Seattle WA


Yes! you'l have an extra unused contact is all.
Alan

"Dan Miller" wrote in message
...
Is it possible to wire a 3 phase switch for two phase power?

TIA

Dan Miller
Seattle WA

Out of curiosity, where are you finding two phase power? To my knowledge,
there is no such in Washington unless there's some old installations
somewhere, perhaps old mines or the like that generate their own power.
Two phase isn't all that common.

Harold

"Alan Black" wrote: Yes! you'l have an extra unused contact is all.
^^^^^^^^^^^^^^
Are you sure you mean two phase? According to my 50-year-old textbook, two
phase is not used--it would need four wires. Are you talking about
single-phase 220, maybe? Then the answer is: "Yes! you'l have an extra
unused conbtact is all." :-)

In article , Dan Miller says...

Is it possible to wire a 3 phase switch for two phase power?

Depends. Where do you have two phase power? That's
very unusual.

Jim

==================================================
please reply to:
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==================================================

"Harold & Susan Vordos" wrote in message ...
"Dan Miller" wrote in message
...
Is it possible to wire a 3 phase switch for two phase power?

TIA

Dan Miller
Seattle WA

Out of curiosity, where are you finding two phase power? To my knowledge,
there is no such in Washington unless there's some old installations
somewhere, perhaps old mines or the like that generate their own power.
Two phase isn't all that common.

Harold

Any polyphase system can be converted to another polyphase system.
In other words, with the proper transformers, three phase can be
converted to two phase, or vice versa. In fact the original wiring
for the Niagara Falls system included both two and three phase systems
interconnected.

Where I used to work, we converted three phase to twelve phase power.
Yes, I did say and mean twelve phase power.

It is possible to have an old two phase system that is derived from
the three phase power company, for older equipment perhaps that is
not necesarily derived from a private generator.

Perhaps Bruce will jump in with a great reference to a wiring diagram
for a Scott-T transformer.

Interesting isn't it?

Apologies to OP for not having usefull switchgear info.
Pete

Dan Miller wrote:
Is it possible to wire a 3 phase switch for two phase power?

By 2-phase, I assume you mean 2 pole. As in wiring a 220V motor
for example.

I did this with a 3/4 hp exhaust blower for my shop. I bought
a 3 pole squareD switch off eBay for $4 and wired each hot to a
pole. The third one was left empty as Alan said.

Jeff Dantzler (also in the Emerald City)

Is it possible to wire a 3 phase switch for two phase power?


Yes, but one lead of the two-phase line will not be switched, and that is now a
no-no.

According to my 50-year-old textbook, two
phase is not used--it would need four wires.


Two-phase can be three, four or five wires, with four wires being the most
common.

Where the source is three-phase, a customer-owned Scott-T transformer is
usually used, in which case the secondary of said transformer is used to
"separately derive" the two-phase system, thereby allowing three wires to be
used for two-phase.

This would be the logical equivalent of grounded Delta three-phase, which has
only two ungrounded wires, yet delivers true three-phase.

Sorry, I did think that he meant single phase. If 4 wire two phase is two
hots 90 degrees apart and two companion neutrals , I'm not sure if you need
to switch the neutrals too. Of course with three phase you must switch all
three.
Alan

"A closed mouth gathers no feet"


Is it possible to wire a 3 phase switch for two phase power?


Yes, but one lead of the two-phase line will not be switched, and that is
now a
no-no.

In article ,
Alan Black wrote:
Sorry, I did think that he meant single phase.

That is a reasonable assumption, given the relative rarity of
real two-phase power form the company, and the fairly common mistaken
assumption that the 220V is two phase.

If 4 wire two phase is two
hots 90 degrees apart and two companion neutrals , I'm not sure if you need
to switch the neutrals too. Of course with three phase you must switch all
three.
Alan

And another question is what kind of load is planned? Assuming
that he really *did* mean 220V single phase to something like a
reversible lathe motor, then he will need all three sets of contacts (on
a typical drum switch) to be able to start the motor in either
direction.

For a single direction of operation from 220V single phase
(neutral center tap), you can get away with only two contacts.

Enjoy,
DoN.
--
Email: | Voice (all times): (703) 938-4564
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--- Black Holes are where God is dividing by zero ---

Dan Miller :

Is it possible to wire a 3 phase switch for two phase power?

Peter H. wrote:

Yes, but one lead of the two-phase line will not be switched, and that is
now a no-no.

Can you elaborate on this?

I assumed the OP meant single phase 240V (L1 & L2).

In my case, I switched a single phase, 240V motor with a 3-pole switch.
My understanding was that the switch could be used for a 3-phase device
because all 3-poles open or close simultaneously. I simply connected each
hot to a pole and then provided a proper equipment ground. The middle pole
(switched contacts) was not connected to anything.

This wouldn't strike me as being a code violation, but I have not looked
at the most recent NEC.

Did you mean one line always hot and the other switched for a 240V load?

Jeff Dantzler

In article , DoN. Nichols says...

And another question is what kind of load is planned? Assuming
that he really *did* mean 220V single phase to something like a
reversible lathe motor, then he will need all three sets of contacts (on
a typical drum switch) to be able to start the motor in either
direction.

One can do this with three contacts as long as the motor is a
120/240 volt motor, because of the peculiarity that when those
are wired for the higher voltage, the start winding is tied
to the *center* *tap* of the run windings (which are in series
when wired for 240) and can thus be reversed with a single
contact, as shown in this diagram:

http://www.metalworking.com/DropBox/_2001_retired_files/wire.jpg

There is an associated text file with that,

http://www.metalworking.com/DropBox/_2001_retired_files/wire.txt

I think that reversing a single-voltage 240 volt motor would
in principle require four contacts.

Jim

==================================================
please reply to:
JRR(zero) at yktvmv (dot) vnet (dot) ibm (dot) com
==================================================

On Sat, 12 Jun 2004 00:02:22 GMT, "Alan Black" wrote:
Sorry, I did think that he meant single phase. If 4 wire two phase is two
hots 90 degrees apart and two companion neutrals , I'm not sure if you need
to switch the neutrals too. Of course with three phase you must switch all
three.

There aren't any neutrals in a 4 wire 2 phase system. All 4 wires are hot.

Gary

Hi Gary,
I have had no personal experience with wiring a 2 phase system, but my
"American Electricians Handbook" Eleventh edition Page 3-10, Fig. 3-23, Fig
17 shows 2 phase, 4 wire as two separate single phase circuits 90 degrees of
phase apart. You are correct in that it does not call one of the conductors
in a single phase two wire circuit a "neutral" either (Fig. 14)
But in the diagram there is no "voltage relation" between the two pairs.
So possibly using the term "neutral" on my part was not technically correct
unless it is a accepted term to describe one of the conductors of a single
phase circuit. In either event it seems that you can switch a 2 phase, 4
wire, circuit with two poles as it would interrupt each of the pairs
satisfactorily.
After all the discussion fun as it is, of greater curiosity is why have
we have not heard a peep from Dan Miller, the original poster of the
question?
Helpfully
Alan

ps ( would you like to have a scan or fax of the chart?)

"Gary Coffman" wrote in message
There aren't any neutrals in a 4 wire 2 phase system. All 4 wires are hot.

Gary

On Sat, 12 Jun 2004 17:18:00 GMT, "Alan Black" wrote:
Hi Gary,
I have had no personal experience with wiring a 2 phase system, but my
"American Electricians Handbook" Eleventh edition Page 3-10, Fig. 3-23, Fig
17 shows 2 phase, 4 wire as two separate single phase circuits 90 degrees of
phase apart. You are correct in that it does not call one of the conductors
in a single phase two wire circuit a "neutral" either (Fig. 14)
But in the diagram there is no "voltage relation" between the two pairs.

The diagram may not show it, but there is a definite voltage relationship between
each of the wires. They're orthogonal to each other, so going around the diamond
clockwise, each adjacent set of wires has a voltage magnitude between them which
is sqrt(2)/2 the pair voltage across each phase pair (polarities at any given snapshot
instant swap as you move from quadrant to quadrant, of course).

So possibly using the term "neutral" on my part was not technically correct
unless it is a accepted term to describe one of the conductors of a single
phase circuit. In either event it seems that you can switch a 2 phase, 4
wire, circuit with two poles as it would interrupt each of the pairs
satisfactorily.

Neutral is a term used to describe a conductor about which all other voltages
in the system are symmetric. The term fits for the centertap in a single phase
240 volt residential system. It also fits in a 4 wire 3 phase wye system. But the
symmetry point doesn't have a wire in a 3 phase delta system or in a 2 phase
4 wire system. So there is no neutral. All conductors are hot with respect to
each other, and are at some undefined potential with respect to Earth.

In a residential system, neutral is bonded to Earth at the entrance panel. So
it is safe to not interrupt it when you switch a 120 volt circuit. But the other
systems don't have any of the wires bonded to Earth (there are exceptions to
this such as corner ground delta, but I'll ignore the exceptions here), so it is
necessary to switch all the hots in order to assure the circuit is cold, ie if you
were to want to work on the wiring downstream of the switch, for example.

After all the discussion fun as it is, of greater curiosity is why have
we have not heard a peep from Dan Miller, the original poster of the
question?

Well, hopefully he didn't fry himself.

Gary

.. They're orthogonal to each other, so going around the diamond
clockwise, each adjacent set of wires has a voltage magnitude between them
which
is sqrt(2)/2 the pair voltage across each phase pair (polarities at any
given snapshot
instant swap as you move from quadrant to quadrant, of course).



Ah! That explains the 90 degrees, 90X4=360, but if that is the case why
wouldn't be 4 phase?


Well, hopefully he didn't fry himself.

Literally or figuratively....


Alan

In article ,
jim rozen wrote:
In article , DoN. Nichols says...

And another question is what kind of load is planned? Assuming
that he really *did* mean 220V single phase to something like a
reversible lathe motor, then he will need all three sets of contacts (on
a typical drum switch) to be able to start the motor in either
direction.

One can do this with three contacts as long as the motor is a
120/240 volt motor, because of the peculiarity that when those
are wired for the higher voltage, the start winding is tied
to the *center* *tap* of the run windings (which are in series
when wired for 240) and can thus be reversed with a single
contact, as shown in this diagram:

http://www.metalworking.com/DropBox/_2001_retired_files/wire.jpg

Agreed. I have posted ASCII schematics in the past to show
this.

I think that reversing a single-voltage 240 volt motor would
in principle require four contacts.

Nope -- as long as you have one end of the 240 as neutral (as in
the UK, where single-voltage motors are more common) or are willing to
leave one side of the motor hot (unswitched).

Let's see -- with ASCII drawings for the switching (as usual,
view with a fixed pitch font, like Courier, to avoid distortion):


o------+----------------------------------------------+
L(240V) A | |
o----+-----o------o | |
| |
o------+ +-------Start Cap |
| | |
+--------------------+ V +--Centrifugal Switch |
| Y V 3
| o--------+-|(--o---o-+ 3
| B | | Run 3
+-----o------o | 3 Winding 3
| 3 3
o----+ | 3 Start 3
| | 3 Winding 3
o----+ | 3 3
N (0V) C | | 3 3
o----+-----o------o | | 3 |
| | | 3 |
| o--------+ 3 |
| | | |
| +----------------+ |
| Z |
+-------------------------------------------------------------------+

The center position will probably not have any contacts associated with
it, but I drew them to show that there was an off position for the
switch.

Switch section A switches power to everything (except the
neutral side of the main winding. Switch sections B and C essentially
reverse the connections to points Y and Z, and are sometimes pre-cross
wired to normally reverse two of the three wires on a three-phase motor.

Obviously, if using this on US 240V line, you want to especially
make sure that everything is unplugged before working on the wiring, as
there will be more points still hot than otherwise would be found.

Note -- this probably violates code in the US, but it shows that
it *can* be done with three switch sections. As a matter of fact, I
suspect that this was how my Clausing was wired when I received it. I
very soon rewired it for 220V because it was in the habit of popping the
breaker when I started it (say one time out of fifteen -- enough to be a
nuisance. :-) I didn't bother tracing out how they had done it, I just
went straight for 220V operation.


Enjoy,
DoN.
--
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---

My guess is he probably was talking about single phase.

But 2 phase power was common, and is still occasionally found, in two
places I know of- Buffalo New York, and Philadelphia Penn. Since both
of these places were wired very early in the history of
electrification, and they were industrial centers in the 19th century,
they got pretty far in using 2 phase before the single phase/ three
phase system was settled upon as a standard.
As a result, you still find the occasional used machine tool in PA or
NY that has a 2 phase motor on it, and there are still shops wired
that way there.

Sorry Guys!

I used to frequent this news group quite often and haven't as of late.

I posted this question a while back and just now decided to log in and see
if there was any
response!

Thanks for all of your very interesting discussion! I must say I learned a
lot regardless of the fact
that I meant (as some of you assumed) regular (I guess you would call it
single pole or single phase) power. You know, 120 volts AC right out of the
standard hosehold plug here in the U.S.

You see, I bought a nice push button switch for my drill press off of E-bay
knowing it was a 3 phase switch but
now I'm a bit confused on how to wire it for my single phase power. Should I
just break the black wire over two of the contacts of the switch and leave
the other three open? I'd ground the motor as well of course.

Thanks again, I promise to not let you guys hang in endless discussion of
what I may have "meant" again.

Dan


"Peter H." wrote in message
...


According to my 50-year-old textbook, two
phase is not used--it would need four wires.


Two-phase can be three, four or five wires, with four wires being the most
common.

Where the source is three-phase, a customer-owned Scott-T transformer is
usually used, in which case the secondary of said transformer is used to
"separately derive" the two-phase system, thereby allowing three wires to
be
used for two-phase.

This would be the logical equivalent of grounded Delta three-phase, which
has
only two ungrounded wires, yet delivers true three-phase.

In article ,
Dan Miller wrote:

[ ... ]

Thanks for all of your very interesting discussion! I must say I learned a
lot regardless of the fact
that I meant (as some of you assumed) regular (I guess you would call it
single pole or single phase) power. You know, 120 volts AC right out of the
standard hosehold plug here in the U.S.

O.K.

You see, I bought a nice push button switch for my drill press off of E-bay
knowing it was a 3 phase switch but
now I'm a bit confused on how to wire it for my single phase power. Should I
just break the black wire over two of the contacts of the switch and leave
the other three open? I'd ground the motor as well of course.

O.K. You can use any one of the contact pairs for switching the
hot (black) wire. Or if the motor draws near the limit of the switch
(the rating should be molded into the plastic), you can parallel two or
three contacts to handle a bit more current. (Probably not triple the
rating, as the contacts probably don't open and close at precisely the
same time, but it will help a bit.

I presume that this does not have a button for "reverse" to
complicate things?

Good Luck,
DoN.
--
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---

In article , DoN. Nichols says...

Note -- this probably violates code in the US, but it shows that
it *can* be done with three switch sections.

Eeeek. I've done a lot of sketchy things in the past, but
I would really really try to avoid doing that - wiring a
machine for 240 with one leg always hot (unswitched). Aside
from the code violation, I don't think I could sleep at
night knowing that the motor had 120 between the windings
and the frame, and that an insulation breakdown could
cause trouble.

I would only do that for temporary testing, or if I had
to run it that way long term for whatever reason, I see that
it could be unplugged when not in use.

Jim

==================================================
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==================================================

Thans Don,

No reverse button....

I appreciate your help

Dan
"DoN. Nichols" wrote in message
...
In article ,
Dan Miller wrote:

[ ... ]

Thanks for all of your very interesting discussion! I must say I learned
a
lot regardless of the fact
that I meant (as some of you assumed) regular (I guess you would call it
single pole or single phase) power. You know, 120 volts AC right out of
the
standard hosehold plug here in the U.S.

O.K.

You see, I bought a nice push button switch for my drill press off of
E-bay
knowing it was a 3 phase switch but
now I'm a bit confused on how to wire it for my single phase power.
Should I
just break the black wire over two of the contacts of the switch and
leave
the other three open? I'd ground the motor as well of course.

O.K. You can use any one of the contact pairs for switching the
hot (black) wire. Or if the motor draws near the limit of the switch
(the rating should be molded into the plastic), you can parallel two or
three contacts to handle a bit more current. (Probably not triple the
rating, as the contacts probably don't open and close at precisely the
same time, but it will help a bit.

I presume that this does not have a button for "reverse" to
complicate things?

Good Luck,
DoN.
--
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---

Thanks for all of your very interesting discussion! I must say I
learned
a
lot regardless of the fact

Too Funny, I like this group, beers on me!
Alan

On 12 Jun 2004 20:42:59 -0700, jim rozen
wrote:

Eeeek. I've done a lot of sketchy things in the past, but
I would really really try to avoid doing that - wiring a
machine for 240 with one leg always hot (unswitched). Aside
from the code violation, I don't think I could sleep at
night knowing that the motor had 120 between the windings
and the frame, and that an insulation breakdown could
cause trouble.

I have an ingersol-rand 5 hp 3ph air compressor that I rebuilt for a
customer (and he aint getting it until he pays me..) that only has two
pair of contacts for the power. When it came to me, the third leg was
constant hot. And its factory original, which is completely weird.

Gunner

That rifle hanging on the wall of the working-class flat or labourer's
cottage is the symbol of democracy. It is our job to see that it stays
there.
- George Orwell

In article , Gunner says...

On 12 Jun 2004 20:42:59 -0700, jim rozen
wrote:

Eeeek. I've done a lot of sketchy things in the past, but
I would really really try to avoid doing that - wiring a
machine for 240 with one leg always hot (unswitched). Aside
from the code violation, I don't think I could sleep at
night knowing that the motor had 120 between the windings
and the frame, and that an insulation breakdown could
cause trouble.

I have an ingersol-rand 5 hp 3ph air compressor that I rebuilt for a
customer (and he aint getting it until he pays me..) that only has two
pair of contacts for the power. When it came to me, the third leg was
constant hot. And its factory original, which is completely weird.

Maybe it was specially designed to run on grounded leg delta
service? My experience is that manufacturers tend to leave
the specifics of contactors and wiring to the local electricians,
so machines will come missing the last link that hooks up to
the local service.

Jim

==================================================
please reply to:
JRR(zero) at yktvmv (dot) vnet (dot) ibm (dot) com
==================================================

In article ,
says...
In article , Gunner says...

On 12 Jun 2004 20:42:59 -0700, jim rozen
wrote:

Eeeek. I've done a lot of sketchy things in the past, but
I would really really try to avoid doing that - wiring a
machine for 240 with one leg always hot (unswitched). Aside
from the code violation, I don't think I could sleep at
night knowing that the motor had 120 between the windings
and the frame, and that an insulation breakdown could
cause trouble.

I have an ingersol-rand 5 hp 3ph air compressor that I rebuilt for a
customer (and he aint getting it until he pays me..) that only has two
pair of contacts for the power. When it came to me, the third leg was
constant hot. And its factory original, which is completely weird.

Maybe it was specially designed to run on grounded leg delta
service? My experience is that manufacturers tend to leave
the specifics of contactors and wiring to the local electricians,
so machines will come missing the last link that hooks up to
the local service.


I think it may have been legal at one time to switch only
two leads of a three 3 phase motor. My 60s vintage IR
compressor has a Square D pressure switch nameplate rated
5HP @ 240V, 3 phase, but is only a 2-pole switch.

I know that it used to be acceptable to put overload
heaters on only two poles of a motor starter, and this is
no longer the case.

Ned Simmons

"Ned Simmons" wrote in message
...
In article ,

I think it may have been legal at one time to switch only
two leads of a three 3 phase motor. My 60s vintage IR
compressor has a Square D pressure switch nameplate rated
5HP @ 240V, 3 phase, but is only a 2-pole switch.

I know that it used to be acceptable to put overload
heaters on only two poles of a motor starter, and this is
no longer the case.

Ned Simmons

From the 2002 NEC

Article 430.84
The controller shall not be required to open all conductors
to the motor.
Exception: Where the controller serves also as a disconnection
means, it shall open all ungrounded conductors to the motor
as provided in 430.111
---A controller that does not also serve as a disconnecting
means must open only as many motor circuit conductors as
may be necessary to stop the motor, that is, one conductor
for a DC or single-phase motor circuit, two conductors for
a 3-phase motor circuit, and three conductors for a 2-phase
motor circuit.---


Nate

--
http://www.Weber-Automation.net:8000

In article ,
says...
"Ned Simmons" wrote in message
...
In article ,

I think it may have been legal at one time to switch only
two leads of a three 3 phase motor. My 60s vintage IR
compressor has a Square D pressure switch nameplate rated
5HP @ 240V, 3 phase, but is only a 2-pole switch.

I know that it used to be acceptable to put overload
heaters on only two poles of a motor starter, and this is
no longer the case.

Ned Simmons

From the 2002 NEC

Article 430.84
The controller shall not be required to open all conductors
to the motor.
Exception: Where the controller serves also as a disconnection
means, it shall open all ungrounded conductors to the motor
as provided in 430.111
---A controller that does not also serve as a disconnecting
means must open only as many motor circuit conductors as
may be necessary to stop the motor, that is, one conductor
for a DC or single-phase motor circuit, two conductors for
a 3-phase motor circuit, and three conductors for a 2-phase
motor circuit.---



I'm sure I've read that section, but that never registered.

Ned Simmons

In article ,
Nate Weber wrote:
"Ned Simmons" wrote in message
...
In article ,

[ ... ]

I know that it used to be acceptable to put overload
heaters on only two poles of a motor starter, and this is
no longer the case.

Well ... the heaters sense the current to the motor, and the
third can be no worse than the sum of the two being monitored, so it
should be possible to detect any kind of fault circuit (the most common
being that of power applied to only two phases, which would be feeding a
stalled motor, and thus be sufficiently over-current to trip the circuit
fairly quickly anyway.) This is intended to protect the motor, not
anything else, as there should be a breaker or a fuse in each hot anyway
to protect everything else.

Ned Simmons


From the 2002 NEC

Article 430.84
The controller shall not be required to open all conductors
to the motor.
Exception: Where the controller serves also as a disconnection
means, it shall open all ungrounded conductors to the motor
as provided in 430.111
---A controller that does not also serve as a disconnecting
means must open only as many motor circuit conductors as
may be necessary to stop the motor, that is, one conductor
for a DC or single-phase motor circuit, two conductors for
a 3-phase motor circuit, and three conductors for a 2-phase
motor circuit.---

This means that my earlier circuit to reverse a 220V
single-phase motor with a single three-pole double-throw center off
switch would be legal, as long as there was a disconnect provided
(which in my case would have been the twist-lock power connector near
the lathe).

However, I agree with others that the idea of keeping one side
of the motor live does not feel right anyway.

Thanks,
DoN.
--
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---

On Sat, 12 Jun 2004 19:31:32 GMT, "Alan Black" wrote:
. They're orthogonal to each other, so going around the diamond
clockwise, each adjacent set of wires has a voltage magnitude between them
which
is sqrt(2)/2 the pair voltage across each phase pair (polarities at any
given snapshot
instant swap as you move from quadrant to quadrant, of course).



Ah! That explains the 90 degrees, 90X4=360, but if that is the case why
wouldn't be 4 phase?

It could be called that, but by convention a 180 degree phase shift is
considered only a periodic polarity reversal.

Gary

On Sun, 13 Jun 2004 20:46:18 -0500, "Nate Weber"
wrote:

"Ned Simmons" wrote in message
...
In article ,

I think it may have been legal at one time to switch only
two leads of a three 3 phase motor. My 60s vintage IR
compressor has a Square D pressure switch nameplate rated
5HP @ 240V, 3 phase, but is only a 2-pole switch.

I know that it used to be acceptable to put overload
heaters on only two poles of a motor starter, and this is
no longer the case.

Ned Simmons

From the 2002 NEC

Article 430.84
The controller shall not be required to open all conductors
to the motor.
Exception: Where the controller serves also as a disconnection
means, it shall open all ungrounded conductors to the motor
as provided in 430.111
---A controller that does not also serve as a disconnecting
means must open only as many motor circuit conductors as
may be necessary to stop the motor, that is, one conductor
for a DC or single-phase motor circuit, two conductors for
a 3-phase motor circuit, and three conductors for a 2-phase
motor circuit.---


Nate


Hey Nate,

And as just a follow-up to that, we used MG sets that were operated
Star-Delta. These were effectively 6 lead motors, at 575 to 600 volts
AC producing 0 to 240 volts DC, or sometimes PWM DC. The AC end of
the MG's had three "hot" leads at all times, and the motor is started
and run by switching the other three leads at the controller. That
way, a whole contactor, valued at from $50 to $250 (depending on size)
was "saved". Only problem is, these MG's sit for at least 50% of the
time in a shut-down state, but the 600 volts is still a potential on
the windings, and these MG's would blow the AC ends at a much higher
rate than the same models in a more conventional "all motor leads
open" type.

Take care.

Brian Lawson,
Bothwell, Ontario.

In article , Gary Coffman says...

It could be called that, but by convention a 180 degree phase shift is
considered only a periodic polarity reversal.

By electricians.

Jim

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In article , DoN. Nichols says...

From the 2002 NEC

...must open only as many motor circuit conductors as
may be necessary to stop the motor,...

This means that my earlier circuit to reverse a 220V
single-phase motor with a single three-pole double-throw center off
switch would be legal, as long as there was a disconnect provided
(which in my case would have been the twist-lock power connector near
the lathe).

But then again, that was then. This OTOH would be 2004 so
to be absolutely certain that code book should be inspected.

Jim

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On Mon, 14 Jun 2004 08:46:58 -0400, Brian Lawson
wrote:


And as just a follow-up to that, we used MG sets that were operated
Star-Delta. These were effectively 6 lead motors, at 575 to 600 volts
AC producing 0 to 240 volts DC, or sometimes PWM DC. The AC end of
the MG's had three "hot" leads at all times, and the motor is started
and run by switching the other three leads at the controller. That
way, a whole contactor, valued at from $50 to $250 (depending on size)
was "saved". Only problem is, these MG's sit for at least 50% of the
time in a shut-down state, but the 600 volts is still a potential on
the windings, and these MG's would blow the AC ends at a much higher
rate than the same models in a more conventional "all motor leads
open" type.

Okay, that was false economy in action... But I don't see new
equipment built that way anymore, we've learned better.

(Though I catch pool men "handymanning" their own electric and
single-pole switching 240V pump motors all the time because they
/don't/ know any better. When I get to a complex where the controls
are screwed up, they complain about blowing out new motors, and I
learn the Pool Man has worked on the wiring, they come /all/ the way
apart for a full inspection...)

An example - modern hydraulic elevator machines with open
"submersible" pump motors in the oil tank that are run with 208V
Star-Delta starters, and they have two contactors in the controller.
(Even if you don't have access to the equipment room, the second
"clunk!" is quite audible from outside.) One for total shutdown, the
other for the Delta switch when up to speed.

They do have a second contactor involved, but the complexity of the
starter must be outweighed by the longevity of the motor. Especially
since the hydraulic oil might get traces of moisture in it. That and
if the motor shorts out there's 50 or so gallons of oil there.

(There is also a sticker on the top of the tank to not use water
based hydraulic fluids. Well, Duh....) ;-P

-- Bruce --
--
Bruce L. Bergman, Woodland Hills (Los Angeles) CA - Desktop
Electrician for Westend Electric - CA726700
5737 Kanan Rd. #359, Agoura CA 91301 (818) 889-9545
Spamtrapped address: Remove the python and the invalid, and use a net.

In article , dnichols@d-
and-d.com says...
In article ,
Nate Weber wrote:
"Ned Simmons" wrote in message
...
In article ,

[ ... ]

I know that it used to be acceptable to put overload
heaters on only two poles of a motor starter, and this is
no longer the case.

Well ... the heaters sense the current to the motor, and the
third can be no worse than the sum of the two being monitored, so it
should be possible to detect any kind of fault circuit (the most common
being that of power applied to only two phases, which would be feeding a
stalled motor, and thus be sufficiently over-current to trip the circuit
fairly quickly anyway.)

A fault to ground in a leg with no heater would not trip
the overload if the feed was Y connected.

This is intended to protect the motor, not
anything else, as there should be a breaker or a fuse in each hot anyway
to protect everything else.

That's the primary purpose of the overload, but since the
overcurrent protection in a motor branch circuit can be
much higher than the ampacity of the conductors, the
overloads appear to provide some protection for the
conductors as well.


Ned Simmons


From the 2002 NEC

Article 430.84
The controller shall not be required to open all conductors
to the motor.
Exception: Where the controller serves also as a disconnection
means, it shall open all ungrounded conductors to the motor
as provided in 430.111
---A controller that does not also serve as a disconnecting
means must open only as many motor circuit conductors as
may be necessary to stop the motor, that is, one conductor
for a DC or single-phase motor circuit, two conductors for
a 3-phase motor circuit, and three conductors for a 2-phase
motor circuit.---

This means that my earlier circuit to reverse a 220V
single-phase motor with a single three-pole double-throw center off
switch would be legal, as long as there was a disconnect provided
(which in my case would have been the twist-lock power connector near
the lathe).

However, I agree with others that the idea of keeping one side
of the motor live does not feel right anyway.


And most industrial practice would agree. I've seen
hundreds, if not thousands, of installed motor starters and
can't recall any where all the hots were not switched, even
on old installations with two heaters on three phase
starters.

Ned Simmons

In article ,
says...
In article , DoN. Nichols says...

From the 2002 NEC

...must open only as many motor circuit conductors as
may be necessary to stop the motor,...

This means that my earlier circuit to reverse a 220V
single-phase motor with a single three-pole double-throw center off
switch would be legal, as long as there was a disconnect provided
(which in my case would have been the twist-lock power connector near
the lathe).

But then again, that was then. This OTOH would be 2004 so
to be absolutely certain that code book should be inspected.


The 2002 version is still current.

Ned Simmons

In article , Ned Simmons
says...

This means that my earlier circuit to reverse a 220V
single-phase motor with a single three-pole double-throw center off
switch would be legal, as long as there was a disconnect provided
(which in my case would have been the twist-lock power connector near
the lathe).

But then again, that was then. This OTOH would be 2004 so
to be absolutely certain that code book should be inspected.


The 2002 version is still current.

Thanks for the heads-up. I do know that things change
in code like that over time.

Jim

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