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.
"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." :-)
Depends. Where do you have two phase power? That's
please reply to:
JRR(zero) at yktvmv (dot) vnet (dot) ibm (dot) com
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
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.
By 2-phase, I assume you mean 2 pole. As in wiring a 220V motor
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)
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
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
"A closed mouth gathers no feet"
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.
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
For a single direction of operation from 220V single phase
(neutral center tap), you can get away with only two contacts.
Dan Miller :
Peter H. wrote:
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?
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:
There is an associated text file with that,
I think that reversing a single-voltage 240 volt motor would
in principle require four contacts.
please reply to:
JRR(zero) at yktvmv (dot) vnet (dot) ibm (dot) com
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
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
ps ( would you like to have a scan or fax of the chart?)
"Gary Coffman" wrote in message >
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
instant swap as you move from quadrant to quadrant, of course).
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
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
were to want to work on the wiring downstream of the switch, for example.
Well, hopefully he didn't fry himself.
Agreed. I have posted ASCII schematics in the past to show
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):
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 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.
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.
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
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.