Good question, ive often questioned how psc motor operate at either. Ude be best off to consult a manufacturer

Sent from my SM-G550T2 using Tapatalk

 

I don't think so, amp draw across all three legs needs to be fairly equal. using only two legs is not allowed per electrical code. install the correct breaker in the panel and abandon the extra conductor

 

I don't know for Japan, but here in America you have single phase or three phase the difference being if you are using one or two power "legs", or whether you are using 3 power "legs". The 3 phase has different voltages it could be, and you can also have a wild leg present depending on how the type of 3 Phase. Sounds like you should have an electrician handle this. Or brush up on your electrical. I don't want you to get hurt.

 

Yep just change the breaker to a single phase and cap off the extra wire


Sent from my iPad using Tapatalk

 

Thanks for replies, here is some background:
I have not been able to get a straight answer from the manufacturer
The electrician on this project is the one who red-flagged this and asked me for the answers. (the voltages present are in the Typical 3 phase WYE, which means the actual voltage to the unit would be about 203v, which is well above the minimum requirement of 187v)
As far as the code, I cannot make any representation there (I'm not an electrician), other than that he is licensed, and the premises are being inspected by the local CEO.

I'm just surprised that no one from my distributor to the manufacturers representatives he has spoken to do not have an answer to this question

 

Oh, and the electrician did assure me he has accounted for the amp draw, and will be able to properly distribute load across the three legs, even if we ultimately add these heat pumps to the electrical supply for the building.

 

Yes you would just wire it up for 208 volts and use a two pole breaker in the 3 phase circuit box.(depending if code allows this)

 

The boards in these systems use the opposite polarity in the 240v single phase to smooth out the electrical signal to supply power to various components of the system. Among other things, this allows the system to be free from the 60hz frequency so that they can operate more efficiently. Basically, the sine wave is removed, so the power behaves more like a DC signal. This power can then manipulated to an "AC commutated" power supply to the compressor, which uses an ECM motor.

One of the things I've been told is that if you were to supply both poles of the unit with power from one leg, it might function OK in air conditioning mode, but might freak out once you switched to heat mode(uses more power)

My concern is thus: any two poles off three phase would not be fully opposite, and might cause problems with the boards. Has anyone heard of someone trying this, and what was the result?

 

What do you mean by that? Only difference is the voltage. Make sure there is not a high leg and you will be just fine. Check your voltage to neutral or ground

Sent from my SM-G935V using Tapatalk

 

Well single phase is 180degrees apart electrically and 208 is always from 2 legs 120 degrees apart. It must not matter though as others have stated.

Sent from my SM-G550T2 using Tapatalk

 

There is really only one issue. Let me elaborate.

A three phase panel is not so much of a problem for most uses. You would merely install a two pole breaker, and run conductors just as you would for any other single phase 208 volt-acceptable circuit.

The difference is that a typical single phase panel is derived from a single secondary winding, which is center tapped for a neutral, so you can run 120 volt appliances. When you use the two pole breaker in a single phase panel, you are essentially connecting to either end of the full secondary winding. This means that each end of the winding is at an opposite polarity from the other at any given moment. This is referred to as the two conductors being 180 degrees out of phase with each other.

When you use two phase legs of a three phase panel, your power legs are only 120 degrees apart instead of 180 degrees.

Most of the time, this is not a source of any concern. However, your electrician is right to question this, because we have no idea if it will make a difference in an inverter design. it is certainly possible to design an inverter system where this will not be an issue, but only the manufacturer can tell you if this is the case.

There is no code objection to using a two pole breaker in a three phase panel.

Hope this helps.

 

I think you should get a real electrician involved. You most likely have 208 between each of the lines and 120 volts from each line to neutral. No high leg. If your unit says 208 you should be fine.

 

the phases of a 3 phase are 120 degrees, or 1/3 second apart. each leg carries one leg each of 2 phases. so any two legs supply one phase only, just like residential.

High leg only matters if you're using a hot leg and neutral. legs a-b,b-c,c-a are 240 volts, but a,b,c are 120, 120, 180 volts to ground/neutral

 

That seems to be the general consensus. I wonder if anyone has done this?

 

It sounds like he does have a real electrician. For the electrician to alert Adamatim1 about the degree issue makes me think the guy knows what he's talking about.

Since the manufacturer can't give you an answer I'd call the inverter manufacturer and ask them.

 

Its funny i was changing a capacitor once for an engineer at ohio state. He showed up a little late and began to explain to me how a capacitor works, about phase shift and such...so a asked how single phase motors operate under two legs of 3 phase and he had no real answer. Ive also attempted to google the subject.

Sent from my SM-G550T2 using Tapatalk

 

Why not just get a three phase unit? Making a mountain out of a mole hill.

Sent from my SM-N910W8 using Tapatalk

 

I will add all x-13 or variable speed motors are half step rectified power. Not sure if the differes from a compressor much that takes dc juice. Ive seen some 120v source compressors run of 240vdc power in refrigerators. And 240v compressors run off of 480vdc. The technology is not sound and often fails even in the proper settings. If it says >187v on it ide go ahead and install it. None doing the warranty work would even have a clue what you are talking about anyhow

Sent from my SM-G550T2 using Tapatalk

 

I don't think 3phase inverters are readily available on smaller inverter systems 1/5ton mini splits usually 1 phase. Last summer company I work for replaced 2 libert with 2 x 3 Mitsubishi inverters . But the power requirements were not checked correctly 3 phase liberts removed single phase installed , on start up only ran for several minutes then shut down . I was in the indoor location at first , lost power to roof , had to get site techs involved for access to mains power boards The .3phase supply had voltage sensing overload that tripped the supply as it sensed power only used on 2 circuits . Inserted a 2 pole breaker , worked fine since , so yes can be done , done it several times . As others have said be aware of possible wild legs on the board .

 

I think that everyone should re-read timebuilder words of wisdom. 2 hot legs of a 3 ph power source IS NOT the same thing as 2 hot legs of a res power source.

I have not heard anything negative about using 2 legs of a 3 ph system for a 1 ph inverter HP.

 

op sounds like you are in way over your head. I wish you luck on this project

 

http://electrical-engineering-portal.com/single-phase-power-vs-three-phase-power

hope the link works. Three phase power is 3 single phase currents (1/3 second lag each or 1/3 cycle out of step).

If not, explain why there is so much single phase 120v and single phase 240v equipment on three phase panels? those loads only see one phase, same as in a residential setup. high legs and various voltages are due to the transformer setup out at the pole.

 

I'm not sure what the "1/3 second lag each"means.

If a Commercial Bldg has 208/230 3 ph power,each leg is 120* apart. A Res 208/230 1ph power supply, the two legs are 180* apart.So when a Res(1 ph) ACH System is installed in the Blgd (3 ph)for the Secretary's Coffee Break Room,that AC&H compressor doesn't work quite so well.

Look at it this way! On a 3ph system,w/a 1ph AC. How LOOOOng of a time ,in cycle/sine wave language, is the "electrical hit" missing? On Res ,208/230 1ph the comp gets hit every 180*. Bam,Bam,,On the 3 ph there is a hit at 0*(or 360*) ,then another "hit" at 120*,then nothing at 240*(giving the comp a chance to slow down ,just a little)Bam,Bam ,nobam,KindaSorta.


A Hi Leg is a diff story.

 

Both three-phase and single-phase devices can be powered from a three-phase supply. A three-phase circuit is a combination of three single-phase circuits. The current, voltage, and power relations of balanced three-phase AC circuits can be studied by applying the rules that apply to single-phase circuits.

The sine waves of three-phase voltage are separated by 120 electrical degree because they are generated by three separate sets of armature coils in an AC generator. These three sets of coils are mounted 120 electrical degrees apart on the generator’s armature. The coil ends could all be brought out of the generator to form three separate single-phase circuits, but they are conventionally interconnected so that only three or four wires are actually brought out of the generator.

120 degrees or 1/3 cycle (in time) or, as you pointed out, actually 1/180th of a second between the sine waves. 1/3 second still hits each phase in turn.

If you think of 3 phase motor as 3 single phase windings on a single shaft, would show how 3 phase motors work better, 3 separate "pushes" at slight delay would give more even power output. Assume the generator at the plant in the same way and you would have 3 pairs or wires feeding from gen to motor. 3 phase power has simply shared two legs or each phase on one wire, in a manner of speaking.

 

It would be helpful if the OP could post a model # of the unit he is trying to install.

 

How are the degrees measured?

Isn't all AC voltage generated as 3 phase at the power plant?



Sent from my iPhone using Tapatalk