What would be the real difference between a piece of equipment that is fed 208V 1Ph as opposesd to 208V 3Ph? I am looking for something a little less obvious than a lower overfall amperage. I am looking for an answer based more on theory and maybe even some actual applications. There's obviously a lot of knowledge and experience on this forum that I don't get to see in the field much. thanks ahead of time, Justin.
208V 1Ph vs. 208V 3Ph?
- Thread starter justin
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Re: 208V 1Ph vs. 208V 3Ph?
The 208 1 ph is a single phase load, a heater for example
The 208 3 ph is a three phase load, a motor for example.
208 is the line to line voltage, just as 240 in your house. It could easily be 120. for small loads 120 may be a bit less expensive as only a single pole circuit breaker is required.
The 208 1 ph is a single phase load, a heater for example
The 208 3 ph is a three phase load, a motor for example.
208 is the line to line voltage, just as 240 in your house. It could easily be 120. for small loads 120 may be a bit less expensive as only a single pole circuit breaker is required.
Re: 208V 1Ph vs. 208V 3Ph?
A designer of electrical systems would never design a 208 volt 3 phase system for a large amount of motors. A motor designed for 208 volts has to be a 200 volt rated motor. A 230 volt motor will smoke on 208 with any prolonged use.
Wye 120/208 volt transformers are for supplying 120 volt single phase loads. 208 volts for power sucks
A designer of electrical systems would never design a 208 volt 3 phase system for a large amount of motors. A motor designed for 208 volts has to be a 200 volt rated motor. A 230 volt motor will smoke on 208 with any prolonged use.
Wye 120/208 volt transformers are for supplying 120 volt single phase loads. 208 volts for power sucks
ryan_618
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- Salt Lake City, Utah
Re: 208V 1Ph vs. 208V 3Ph?
Bennie: I want you to know that I'm not arguing with you, your knowledge of theory far exceeds mine, but what is the best alternitive, besides 480? All I ever see is 3P 120/208 wye
Bennie: I want you to know that I'm not arguing with you, your knowledge of theory far exceeds mine, but what is the best alternitive, besides 480? All I ever see is 3P 120/208 wye
Re: 208V 1Ph vs. 208V 3Ph?
Ryan: When the service is only 120/208 you have no choice but to use motors on the 208, and heaters on single phase 208.
With a large amount of motors and heating equipment, any voltage except 120/208 would be preferred.
PS; Its ok to argue
[ October 06, 2003, 11:44 PM: Message edited by: bennie ]
Ryan: When the service is only 120/208 you have no choice but to use motors on the 208, and heaters on single phase 208.
With a large amount of motors and heating equipment, any voltage except 120/208 would be preferred.
PS; Its ok to argue
[ October 06, 2003, 11:44 PM: Message edited by: bennie ]
Ed MacLaren
Senior Member
Re: 208V 1Ph vs. 208V 3Ph?
In Canada, almost all new (last 20 yrs) buildings of that type have 600/347 volt distribution. 575 volt motors and 347 volt lighting, with transformers supplying 120/208 volts for receptacle circuits.
It is quite common to see 32 fluorescent fixtures on a 15 amp breaker in office schools, etc.
Ed
[ October 07, 2003, 12:03 AM: Message edited by: Ed MacLaren ]
It was the preferred system for office/commercial/institutional buildings for many years.
In Canada, almost all new (last 20 yrs) buildings of that type have 600/347 volt distribution. 575 volt motors and 347 volt lighting, with transformers supplying 120/208 volts for receptacle circuits.
It is quite common to see 32 fluorescent fixtures on a 15 amp breaker in office schools, etc.
Ed
[ October 07, 2003, 12:03 AM: Message edited by: Ed MacLaren ]
Re: 208V 1Ph vs. 208V 3Ph?
Difference between single phase 208V and 3-phase?
1. Motors: 3 phase have inherent starting torque, single phase don't. Larger motors are 3-phase.
2. Installation and operating cost? Single phase: 10A x 208V = 2080VA (1040Va per wire). 10A x 208V x 1.73 =3600VA (1200Va per wire).
3. Single phase is better: Monday night football is not 3-phase!
Difference between single phase 208V and 3-phase?
1. Motors: 3 phase have inherent starting torque, single phase don't. Larger motors are 3-phase.
2. Installation and operating cost? Single phase: 10A x 208V = 2080VA (1040Va per wire). 10A x 208V x 1.73 =3600VA (1200Va per wire).
3. Single phase is better: Monday night football is not 3-phase!
Re: 208V 1Ph vs. 208V 3Ph?
A three phase motor is generally smaller and more efficient than a single phase motor of the same horsepower. Given a choice between 3ph 208 and single, I spec 3 ph 208 over 1 ph. Have to make sure the motor is rated for 208V, 3 ph though. Seems to me to be more and more common especially to have 208/230V ratings.
A three phase motor is generally smaller and more efficient than a single phase motor of the same horsepower. Given a choice between 3ph 208 and single, I spec 3 ph 208 over 1 ph. Have to make sure the motor is rated for 208V, 3 ph though. Seems to me to be more and more common especially to have 208/230V ratings.
al hildenbrand
Senior Member
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- Minnesota
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- Electrical Contractor, Electrical Consultant, Electrical Engineer
Re: 208V 1Ph vs. 208V 3Ph?
Justin,
I like Tom's idea. The hypothetical piece of equipment you are considering will be the "load" that will require a certain amount of power. 208 1? and 208 3? will both provide that power. The piece of equipment will use the power to do "work", that is, produce heat, light, motion, etc. The conversion of the electric energy into the energy of heat, light, motion, etc. will most efficiently be done, based on our modern technology by specific equipment designed for the purpose.
The difference between 1? and 3? comes into play with what makes the specific equipment efficient and economical.
An electric heater doesn't benefit from 3? in the production of heat. . .other factors such as the cost of the equipment, the availability of 3?, installation cost, etc. will drive the decision as to whether to go 1? or 3?.
An electric motor will benefit from 3?, three separate voltages that are identical except for their phase (timing) relationship. The 3? motor is a simpler design because the magnetic fields, that allow the motor to convert the electricity into motion, are made to "move" by simple physical arrangement of the motor windings. The 1? motor, by comparison, must have additional hardware added to it to create the moving magnetic field, thus adding a complexity to the motor design.
Justin,
I like Tom's idea. The hypothetical piece of equipment you are considering will be the "load" that will require a certain amount of power. 208 1? and 208 3? will both provide that power. The piece of equipment will use the power to do "work", that is, produce heat, light, motion, etc. The conversion of the electric energy into the energy of heat, light, motion, etc. will most efficiently be done, based on our modern technology by specific equipment designed for the purpose.
The difference between 1? and 3? comes into play with what makes the specific equipment efficient and economical.
An electric heater doesn't benefit from 3? in the production of heat. . .other factors such as the cost of the equipment, the availability of 3?, installation cost, etc. will drive the decision as to whether to go 1? or 3?.
An electric motor will benefit from 3?, three separate voltages that are identical except for their phase (timing) relationship. The 3? motor is a simpler design because the magnetic fields, that allow the motor to convert the electricity into motion, are made to "move" by simple physical arrangement of the motor windings. The 1? motor, by comparison, must have additional hardware added to it to create the moving magnetic field, thus adding a complexity to the motor design.
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- Lockport, IL
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- Retired Electrical Engineer
Re: 208V 1Ph vs. 208V 3Ph?
It?s hard to get into theory, without having a blackboard and the freedom to get deeply into math. But here?s a sniblet of theory.
Start with two things. (1) Three coils of wire so oriented that they have a common axis (i.e., the axis of the motor?s rotor) and are separated in space by 120 degrees of arc. (2) Three power connections so scheduled that their respective peak values are separated in time by 120 degrees of phase. You will get two extraordinary results. The first is that the magnetic field created in the three coils will rotate about the axis at a constant rate. Note that with no moving parts, we have a rotating magnetic field. That is what causes the rotor to move - it follows the motion of the rotating magnetic field. The second is that the power drawn by the motor is constant. I mean it does not vary from millisecond to millisecond; I am not discussing changes in mechanical load. By contrast, the power drawn by a single phase motor follows the ups and downs of a sine wave, with power being positive most of the time and negative a small part of the time (i.e., the motor is giving power back to the utility). (See the detailed discussion below).
I agree with spsnyder, in that motors above 1 hp should be three phase, rather than single phase, regardless of what voltage is available within the building.
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NOTE: WHAT FOLLOWS LOOKS LIKE MATH. IF YOU DON?T CARE FOR MATH, PLEASE FEEL FREE TO MOVE TO ANOTHER TOPIC.
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I believe that the biggest single advantage of three phase motors relates to power. By this, I specifically mean power in the sense of the rate of use of energy. We have all seen the formulas for single phase power (P=V x I) and three phase power (P = sqrt(3) x V x I) (NOTE: I?m talking about KVA, and not KW, so that we don?t have to consider that bizarre ?power factor thingy?).
I?ll not show the math here, but only talk about the math. It uses trigonometry, which I always enjoyed ? but it may prove distasteful to others. I can send it or post it, if there is an interest. I can also describe how to construct a spreadsheet that shows a clear picture of the results.
First look at single phase: The voltage and current will be out of synch with each other by some amount that has to do with inductive and capacitive loads. But both are sine waves. If you (using trigonometry) multiply the voltage sine wave by the current sine wave (which is generally around 30 degrees behind the voltage), the result will still look something like a sine wave. But it will not have half of the cycle as positive power and half as negative power. It will look like it was lifted up above the zero axis, so that most of the power is positive and only a small part of the bottom of the curve will be negative. What this means is that a single-phase generator is putting out a different amount of power at every moment in time, that the power varies as a smooth curve, and that it is mostly positive (i.e., power is used by the motor).
Now look at balanced three phase: Lets call Va, Vb, Vc, Ia, Ib, and Ic the three voltages and the three currents. The trigonometry would have you multiplying and adding sine waves as follows:
Va TIMES Ia (which is 30 degrees behind Va),
ADDED TO
Vb (which is 120 degrees behind Va) TIMES Ib (which is 30 degrees behind Vb),
ADDED TO
Vc (which is 120 degrees behind Vb) TIMES Ic (which is 30 degrees behind Vc).
This extraordinarily messy set of terms gives a result that is extraordinarily simple: the power is constant! At every moment in time, the power used by a three-phase motor is the same.
It?s hard to get into theory, without having a blackboard and the freedom to get deeply into math. But here?s a sniblet of theory.
Start with two things. (1) Three coils of wire so oriented that they have a common axis (i.e., the axis of the motor?s rotor) and are separated in space by 120 degrees of arc. (2) Three power connections so scheduled that their respective peak values are separated in time by 120 degrees of phase. You will get two extraordinary results. The first is that the magnetic field created in the three coils will rotate about the axis at a constant rate. Note that with no moving parts, we have a rotating magnetic field. That is what causes the rotor to move - it follows the motion of the rotating magnetic field. The second is that the power drawn by the motor is constant. I mean it does not vary from millisecond to millisecond; I am not discussing changes in mechanical load. By contrast, the power drawn by a single phase motor follows the ups and downs of a sine wave, with power being positive most of the time and negative a small part of the time (i.e., the motor is giving power back to the utility). (See the detailed discussion below).
I agree with spsnyder, in that motors above 1 hp should be three phase, rather than single phase, regardless of what voltage is available within the building.
- - - - - - - - - - - - - - - - - - - - - - - - -
NOTE: WHAT FOLLOWS LOOKS LIKE MATH. IF YOU DON?T CARE FOR MATH, PLEASE FEEL FREE TO MOVE TO ANOTHER TOPIC.
- - - - - - - - - - - - - - - - - - - - - - - - -
I believe that the biggest single advantage of three phase motors relates to power. By this, I specifically mean power in the sense of the rate of use of energy. We have all seen the formulas for single phase power (P=V x I) and three phase power (P = sqrt(3) x V x I) (NOTE: I?m talking about KVA, and not KW, so that we don?t have to consider that bizarre ?power factor thingy?).
I?ll not show the math here, but only talk about the math. It uses trigonometry, which I always enjoyed ? but it may prove distasteful to others. I can send it or post it, if there is an interest. I can also describe how to construct a spreadsheet that shows a clear picture of the results.
First look at single phase: The voltage and current will be out of synch with each other by some amount that has to do with inductive and capacitive loads. But both are sine waves. If you (using trigonometry) multiply the voltage sine wave by the current sine wave (which is generally around 30 degrees behind the voltage), the result will still look something like a sine wave. But it will not have half of the cycle as positive power and half as negative power. It will look like it was lifted up above the zero axis, so that most of the power is positive and only a small part of the bottom of the curve will be negative. What this means is that a single-phase generator is putting out a different amount of power at every moment in time, that the power varies as a smooth curve, and that it is mostly positive (i.e., power is used by the motor).
Now look at balanced three phase: Lets call Va, Vb, Vc, Ia, Ib, and Ic the three voltages and the three currents. The trigonometry would have you multiplying and adding sine waves as follows:
Va TIMES Ia (which is 30 degrees behind Va),
ADDED TO
Vb (which is 120 degrees behind Va) TIMES Ib (which is 30 degrees behind Vb),
ADDED TO
Vc (which is 120 degrees behind Vb) TIMES Ic (which is 30 degrees behind Vc).
This extraordinarily messy set of terms gives a result that is extraordinarily simple: the power is constant! At every moment in time, the power used by a three-phase motor is the same.
G
Guest
Guest
Re: 208V 1Ph vs. 208V 3Ph?
For a PoCo it is cheaper to deliver three-phase as it's more constant and balanced (when under load). 3-phase also reduces the size of the transmission lines and feeders.
Re: 208V 1Ph vs. 208V 3Ph?
There is 208 delta to 240/133 wye transformers available, when there is a lot of 240 volt motors.
The derived neutral (star point) is electrically connected to the supply neutral (star point)
[ October 07, 2003, 01:38 PM: Message edited by: bennie ]
There is 208 delta to 240/133 wye transformers available, when there is a lot of 240 volt motors.
The derived neutral (star point) is electrically connected to the supply neutral (star point)
[ October 07, 2003, 01:38 PM: Message edited by: bennie ]
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