Wiring 3 phase switch for 2 phase power

Is it possible to wire a 3 phase switch for two phase power?
TIA
Dan Miller
Seattle WA
Reply to
Dan Miller
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Yes! you'l have an extra unused contact is all. Alan
Reply to
Alan Black
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
Reply to
Harold & Susan Vordos
"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." :-)
Reply to
Leo Lichtman
Depends. Where do you have two phase power? That's very unusual.
Jim
================================================== please reply to: JRR(zero) at yktvmv (dot) vnet (dot) ibm (dot) com ==================================================
Reply to
jim rozen
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
Reply to
Pete Logghe
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)
Reply to
Jeff Dantzler
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.
Reply to
Peter H.
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.
Reply to
Peter H.
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"
Reply to
Alan Black
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 direction.
For a single direction of operation from 220V single phase (neutral center tap), you can get away with only two contacts.
Enjoy, DoN.
Reply to
DoN. Nichols
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?
Jeff Dantzler
Reply to
Jeff Dantzler
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.
Jim
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Reply to
jim rozen
There aren't any neutrals in a 4 wire 2 phase system. All 4 wires are hot.
Gary
Reply to
Gary Coffman
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 >
Reply to
Alan Black
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).
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.
Well, hopefully he didn't fry himself.
Gary
Reply to
Gary Coffman
. They're orthogonal to each other, so going around the diamond
Ah! That explains the 90 degrees, 90X4=360, but if that is the case why wouldn't be 4 phase?
Literally or figuratively....
Alan
Reply to
Alan Black
Agreed. I have posted ASCII schematics in the past to show this.
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.
Reply to
DoN. Nichols
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.
Reply to
Ries
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
Reply to
Dan Miller

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