1PH vs 3PH
- Thread starter TBoomz
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The typical home shop doesn't have access to 3phase without adding some specialized equipment. That's the main reason you'll see people steer clear of 3phase equipment.
You asked a fairly complex question. .......... hmmm ........... Well, 3 phase provides more efficient power.
There are several factors to a power and power transfer, without going down the rabbit hole of electrical theory and application I'll just keep to a simple graph that shows the phase power curves.
All electrical in USA is 60 cycles per second alternating current . All alternating current has a positive side (when power is applied) and a negative side (when there is no power). With 120 volt single phase 1/2 of a sec there is power-1/2 sec there is no power.
Using 220-240 power single phase, in effect it is 2 phase power because there are 2 different power sources operating 180 deg out of phase (It is not called that for theoretical reasons another discussion another time). That means the power source with 220 would only have power go to zero but only for a .0167 of a sec versus 120 volt where there is .5 of a second of no power being applied.
3 phase there is never an interruption of power because there is never a moment when there is no power being applied.
Basic benefits for using 220-240 volt or 3 phase besides more efficient use of the electricity, the less stress on the motor, is smaller wire needed to run the motor. Think about it, you want to use a 5hp motor 120 volt, you would need 40 amp wire #8 is 37 cents/ft. versus 220-240 you would have #12 is 16 cents/ft and 3 phase 230 would be #14... 9 cents/ft, If you are running a shop each run is x 2 or 3. Running alot of single phase 5 hp would get expensive and the energy inefficiency would be 25-30% versus with 3 phase is is 10-13%.
Hope that helps, it is not an easy bumper sticker answer, with electricity never really is. I would recommend everyone with a shop buy an Uglys electrical reference book. You can buy one at Lowe's or Home depot I think they are 14 bucks now, when I got mine it was 3.95.... not much has changed. But, this book explains alot and is essential for anyone who ever needs to wire something up.
There are several factors to a power and power transfer, without going down the rabbit hole of electrical theory and application I'll just keep to a simple graph that shows the phase power curves.
All electrical in USA is 60 cycles per second alternating current . All alternating current has a positive side (when power is applied) and a negative side (when there is no power). With 120 volt single phase 1/2 of a sec there is power-1/2 sec there is no power.
Using 220-240 power single phase, in effect it is 2 phase power because there are 2 different power sources operating 180 deg out of phase (It is not called that for theoretical reasons another discussion another time). That means the power source with 220 would only have power go to zero but only for a .0167 of a sec versus 120 volt where there is .5 of a second of no power being applied.
3 phase there is never an interruption of power because there is never a moment when there is no power being applied.
Basic benefits for using 220-240 volt or 3 phase besides more efficient use of the electricity, the less stress on the motor, is smaller wire needed to run the motor. Think about it, you want to use a 5hp motor 120 volt, you would need 40 amp wire #8 is 37 cents/ft. versus 220-240 you would have #12 is 16 cents/ft and 3 phase 230 would be #14... 9 cents/ft, If you are running a shop each run is x 2 or 3. Running alot of single phase 5 hp would get expensive and the energy inefficiency would be 25-30% versus with 3 phase is is 10-13%.
Hope that helps, it is not an easy bumper sticker answer, with electricity never really is. I would recommend everyone with a shop buy an Uglys electrical reference book. You can buy one at Lowe's or Home depot I think they are 14 bucks now, when I got mine it was 3.95.... not much has changed. But, this book explains alot and is essential for anyone who ever needs to wire something up.
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If you have a chance to get a nice tool and its got 3ph motor, you can get a VFD (variable frequency drive) or a phase converter. The VFD can give you variable speed on your tool, like a lathe or drill press. Also 3ph motors can reverse almost instantly. But like Oka says read up on electricity before you get bit. All the 3ph I have seen are 220v or higher so you can get into some seriously deep water without too much warning.
Roy G
Roy G
My big carp about single phase power is that the motors are actually two motors in one. There's a starting motor (windings) and there's a running motor (windings). There's also gadgetry to disconnect the starting motor once the rotor is turning at an acceptable speed. Another gadget is a capacitor that forces a big charge of electricity to get the rotor to start turning.
I would use #10 wire on a 5hp because of the start load (the 5hp 220-240v = 19 amps) just because of the start demand is roughly 1.25 or 23.75 amps. You could use (into to weeds now) #12 provided everything you use on that line is 90deg Celsius rated THHN wire etc. The problem with electrical and mechanical in general is ... changing one variable changes others within the design or assembly. That is why nothing is a simple 2-3 word answer. Resistance in wire is expressed as heat, therefore, you can up the size of everything to handle the heat just oversize the wire, which usually is cheaper.
It would also depend on how many starts and stops you have, if you turn something on 1-2 times a day, not a big issue, but if you are an elevator where the start and stop is 3-5 a min then, yeah ...BIG issue. It all depends.
Feel free to pm me if you ever have a wire sizing issue.
It would also depend on how many starts and stops you have, if you turn something on 1-2 times a day, not a big issue, but if you are an elevator where the start and stop is 3-5 a min then, yeah ...BIG issue. It all depends.
Feel free to pm me if you ever have a wire sizing issue.
I beg to differ. 240V household power is ONE phase. It most certainly does not use "multiuple power sources." The power source is a single leg of what was almost assuredly a three phase supply. The transformer near your house drops it down to 240V (single phase) with a center tap that provides the 120V that most of your household stuff use.
When you come to discuss motors, you have to talk about what sort of motor you are talking about. Smaller motors (universal or the like) are usually single phase devices that could't use three phase even if it were available. Larger motors are typically induction motors which ,can be three phase for practical purposes or single phase (though the latter requires special provisions to get them started). Most of the commercial stuff comes three phase. If you have three phase available to you, then it would be handy to have it in the shop. Otherwise, you have to deal with single phase motors or deal with a couple of ways of getting a three phase motor to work with a single phase feed.
Wire size doesn't have much to do with phases. The higher the current, the larger the wire size needs to be (and the more loss there is). Since power is voltage times current, you can get by with less current at higher voltages. This is why your motor will run on 9A at 240 but needs 20A at 120.
The other neat feature is that a lot of variable speed stuff these days (like some lathes, etc...) are essentially three phase motors but the phase (and the frequency) is electronically generated from a single phase source (essentially DC).
I've been meaning to write a more concise description of all this. You may see this as an article soon.
When you come to discuss motors, you have to talk about what sort of motor you are talking about. Smaller motors (universal or the like) are usually single phase devices that could't use three phase even if it were available. Larger motors are typically induction motors which ,can be three phase for practical purposes or single phase (though the latter requires special provisions to get them started). Most of the commercial stuff comes three phase. If you have three phase available to you, then it would be handy to have it in the shop. Otherwise, you have to deal with single phase motors or deal with a couple of ways of getting a three phase motor to work with a single phase feed.
Wire size doesn't have much to do with phases. The higher the current, the larger the wire size needs to be (and the more loss there is). Since power is voltage times current, you can get by with less current at higher voltages. This is why your motor will run on 9A at 240 but needs 20A at 120.
The other neat feature is that a lot of variable speed stuff these days (like some lathes, etc...) are essentially three phase motors but the phase (and the frequency) is electronically generated from a single phase source (essentially DC).
I've been meaning to write a more concise description of all this. You may see this as an article soon.
I'm curious as to why you asked this question. Are you in a position to have three phase current coming into your shop if you wanted it?
I knew that comment would get someone sparked up. My electrical engineering instructor and many of us had a spirited about this. That said, Sine A and Sine B are 180 deg out from each other. On the scope it reads as a single phase, but, it is 2 sources of power not one. Either way, the comment is for those who are not understanding of the sine relationships. The comment presents a better visual for those who are not inclined to electrical theory. Still, it is a single phase system albeit 2 sources of power.
Back in my youth, FWW magazine had an article about 3ph power. They described how to make a rotary phase converter and I got the various necessities and made one. At first I would wind a rope around the shaft of the 3ph motor I was going to use as the converter and pull on it to spin the motor as I turned on the 220v single phase to feed it. That got onerous so I wired a capacitor into one of the legs so I sort of jerked it into motion. Surprisingly enough, it worked and I ran several 3ph machines for several years before I got rid of them and no longer needed the big 3ph motor. It was 7.5 hp so I think it was putting out 5 usable hp but I only ran maybe 1 hp 3ph motors off it, one at a time. Over on OWWM.org there is quite a bit of info about phase converters and VFDs for your entertainment.
Roy G
Roy G
There are not "two sources" of power. That statement is nonsensical. Anyhow, you don't have two phases, you're just measuring a single phase with regard to a center point. No sane electrical engineer calls it two phase nor is that term EVER used with regard to the electrical code, etc...
As I recall, certain areas of Philadelphia had two phase power at one time. They may still have it. Probably don't have sane electrical engineers there, though.
Two Phase PECO Utility Service - Philadelphia 610-853-8311.
Ron still hasn't replied as to why he wanted to know about the three phase motors.
Two Phase PECO Utility Service - Philadelphia 610-853-8311.
Ron still hasn't replied as to why he wanted to know about the three phase motors.
Ok We can disagree...... In talking with out Electrical P.E.'s in our office today, They define it as 2 sources of power coming into a building is really 2 distinct sources. They like those in here also disagree on this, Regardless it is more an academic point. The comment was not to incite discontent, but rather demonstrating the point 120v in our elec system in the USA has 1 positive leg, 220-240 has 2 and 3phase has 3, with each starting at a different point. But, to get into the actual theory of this, I think this actually answers it best:
240V has two 120 voltages 180 degrees apart with neutral and ground halfway in the middle between the two voltages. Because The voltages are ½ of the whole, this is why it is called 240 single phase. The voltage measured between the two power legs is 240V, and since neutral is halfway between, the voltage from either leg to neutral would be 120V.
I hope I haven't confused this more, and made it clear as mud. To me, it seems more accurate to consider 120v half wave, and 240 full wave single phase. So, it really is not 2 distinct phases. But, to the layman, the fact still remains it is 2 different power wires each, just like 3 phase has 3 power wires each. Only, 3 phase is 3 separate power sources whereas the 240 system as mentioned above is only 1 power source cut in half.
240V has two 120 voltages 180 degrees apart with neutral and ground halfway in the middle between the two voltages. Because The voltages are ½ of the whole, this is why it is called 240 single phase. The voltage measured between the two power legs is 240V, and since neutral is halfway between, the voltage from either leg to neutral would be 120V.
I hope I haven't confused this more, and made it clear as mud. To me, it seems more accurate to consider 120v half wave, and 240 full wave single phase. So, it really is not 2 distinct phases. But, to the layman, the fact still remains it is 2 different power wires each, just like 3 phase has 3 power wires each. Only, 3 phase is 3 separate power sources whereas the 240 system as mentioned above is only 1 power source cut in half.
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The two hot legs that come into our homes are 2 of the three phases the power was generated in. We do not get all three phases. 220v is line to line. 120V is line to neutral. If you have a 220V feed and want to tap a 120V load into it, you can but your total current load cannot exceed the safe load for the wire. I would not call two phases of one source of power different power sources but I guess you could. If you define power as line to neutral, then it would be two different sources of power. I think back to the generator and all three phases were generated at once.
But 220V motors are normally one phase motors. They have one spinning magnet, three phase motors have three, one per phase.
But the post talking about a phase converter is correct, since we do not get all three phases in our homes we cannot hook them to a motor. We have to create them. I doubt there is a net efficiency gain for a three phase motor driven by a phase converter but I didn't look it up.
The only reason I see to use a three phase motor is that is what a tool you want comes with. Any gain in wire size won't pay for much in the way of a three phase converter or more costly motor.
But 220V motors are normally one phase motors. They have one spinning magnet, three phase motors have three, one per phase.
But the post talking about a phase converter is correct, since we do not get all three phases in our homes we cannot hook them to a motor. We have to create them. I doubt there is a net efficiency gain for a three phase motor driven by a phase converter but I didn't look it up.
The only reason I see to use a three phase motor is that is what a tool you want comes with. Any gain in wire size won't pay for much in the way of a three phase converter or more costly motor.
Look at the distribution wires on the pole outside. There are generally two. Lower, neutral/ground, and upper hot. No matter what kind of transformer is hooked to them, output is still single phase. If overhad is three wires, two hots and neutral/ground, you have two phase available, which require two transformers. Add a third leg, run thru a capacitor, and you can get a "false phase, which will run certain 3 phase motors. Think of remote farms where adding third hot is cost prohibitive, so you just pull a false phase.
I'm a retired EE.
Through all of these responses, only FlyingRon knows what he is talking about. Pay attention to him.
Charley
Through all of these responses, only FlyingRon knows what he is talking about. Pay attention to him.
Charley
hmm,...ask a simple question, and...I'm probably more confused
reading all your comments. But at least others got something out of it.
My shop is wired for 3PH. All the big machines are hardwired in. I have two machines not currently hooked up. Saw this plug and wondered what it was, and if I could use it, but didn't want to risk burning out my 3ph motors.
From the comments, I'm guessing it is 240V single phase. But if theoretically 2PH [as someone mentioned], can I run a 3ph motor off the two legs?
And can i do it straight or would there still be a need for something, inline, between?
reading all your comments. But at least others got something out of it.
My shop is wired for 3PH. All the big machines are hardwired in. I have two machines not currently hooked up. Saw this plug and wondered what it was, and if I could use it, but didn't want to risk burning out my 3ph motors.
From the comments, I'm guessing it is 240V single phase. But if theoretically 2PH [as someone mentioned], can I run a 3ph motor off the two legs?
And can i do it straight or would there still be a need for something, inline, between?
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