- Location
- Connecticut
- Occupation
- Engineer
A 2 phase motor will have 4 leads.
Contractor Exam Prep - Unit 8 Challange question 2
- Thread starter S-117
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A 2 phase motor will have 4 leads.
- Location
- Massachusetts
My suggestion is never use the term '2 phase' again.
As has been mentioned a true 2 phase system or 2 phase motor is rare.
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
Think af a 208 single phase motor as a motor that uses 2 hot legs. Unfortunately the nomenclature makes things confusing because we call it 3 phases-- A Phase, B Phase, and C phase yet when you connect from A to B, or B to C or A to C you are not using 2 phases--- I know it's a mess for many to understand.
I am not sure the NEC requires balancing the loads but in many areas the power company's requires it. Imagine what would happen to their system if everyone installed all 120V loads on "A" Phase
If an engineer calculates the loads then he/she would designate the phases where the loads should be connected
K8MHZ
Senior Member
- Occupation
- Electrician
A '1 phase' motor is NOT wired to two phases.
- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
:thumbsup:
Using the terminology of post #23 it may be wired either to two legs or to one leg and the neutral.
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
Do you not see the issue. We call the service 3 phase and the panel has 3 Hot legs referred to as phases and we hook to 2 of them. Personally I say it is wired to 2 of the 3 phases. Technically wrong but it is spoken like that in the field all day long so why try and change it
K8MHZ
Senior Member
- Occupation
- Electrician
Think of a phase as a line on an oscilloscope, not as a wire.
When you see a single phase on a scope, you will see one sine wave that represents the voltage difference between two conductors.
When you see three phase, you will see three sine waves. One will be the voltage difference between conductor A and B, a second, B and C, and a third, A and C. In three phase, each phase shares a conductor with another phase.
In two phase, there will be two sine waves, One will be the voltage between conductors A and B, and the second phase will be the voltage between conductors C and D. In two phase, conductors are not shared.
In the early days of AC, two phase was present in many areas, as it has advantages over single phase in a factory type setting, especially when it comes to motors. Multi-phase motors are simpler and more reliable than single phase motors.
Then, a few guys decided to try Tesla's 3 phase concept for factory motors. 3 phase has an advantage over 2 phase in that only three wires are needed. 3 phase took off, and the rest is history, except the part about the guy that was the most responsible for the popularity of 3 phase had a falling out with his partners, and never got the credit he deserved. Ironically, factory workers for decades knew his name.....it was on their Thermos bottles. Stanley Thermos bottles.
K8MHZ
Senior Member
- Occupation
- Electrician
Not in my world. Anyone I hear refer to a single conductor as a phase comes off as a noob. Conductors are referred to as legs in my neck of the woods.
And you 'hook' to them?
Nothing personal, I don't think I would last long in your world.
- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
There are a few practical consequences to going along with that common language.
1. For a balanced three phase four wire wye it is correct (or at least acceptable) to say that the VA on one phase is in fact identical to the VA on one leg but
2. It is not correct and is actively misleading to say that the current in one phase is equal to the current on one leg.
The practical problem is in recognizing just where it is necessary to make the distinction between the two.
IMO that makes it a good idea to make an effort to use the clearest possible terminology for all answers in this forum, even where the problem at hand is one where it does not make a practical difference. But without "busting someones chops" for imprecise language.
JoeStillman
Senior Member
- Location
- West Chester, PA
A phase is not a wire; it's a voltage. All voltages are relative, so for a 1Ø voltage you need two wires. It can be two hots or a hot and a neutral but there's always two.
This is what you mean when you say two-phase.
So unless you memorize this diagram, it's a good idea to forget two-phase. (If you live in Philly, like I did, you need to memorize it.)
This is what you mean when you say two-phase.
So unless you memorize this diagram, it's a good idea to forget two-phase. (If you live in Philly, like I did, you need to memorize it.)
K8MHZ
Senior Member
- Occupation
- Electrician
Technically, the voltages are not identical. They show 'identical' RMS readings on the meters we use, but in multi-phase AC, at any given moment the voltages are different, never the same, from phase to phase. Each phase goes from a max pos. value to a max neg. value, through the 0 crossing line, but not all at the same time.
Contrarily, the current CAN be identical on all three phases at any given time, and can be zero and still be three phase. If the voltage goes to 0 and stays there, we have no phases.
jumper
Senior Member
- Location
- 3 Hr 2 Min from Winged Horses
:thumbsup:
First code class I ever took the teacher(our local inspector) had us use a pencil and X out Table 430.249 so we would never screw up and use it on accident in class or on a test.
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