single vs. 3 phase

[grantcool]

why is 2 phase - 240 volt - called single phase???

 

[iwire]

Your best bet is to just accept it.

This question is bound to generate a ton of responses. :grin:

There is another type of uncommon electrical system called "Two Phase" but that is almost nonexistent as far as I know.

 

[76nemo]

I too have gone round and round on that with some others. Before this takes off again like deadly broken records, do a search for "Battle of the Phases". Start from there,.............................

 

[mdshunk]

why is 2 phase - 240 volt - called single phase???

I guess because single-phase is not 2-phase, for one. Two-phase is an old system that bears little resemblance to single phase.

 

[EBFD6]

Why do we call them 3-way switches when there are only two of them?

Some things just are what they are.

Like Iwire said, this is just one of those things we have to accept and move on:smile:

 

[raider1]

Why do we call them 3-way switches when there are only two of them?

That question can be answered HERE

Chris

 

[grantcool]

can of worms

can of worms

my God, i just looked up the hundreds of old (and still going) threads on this subject and now realize that it would be better to just accept things the way they are and go on my merry way........

 

[Psychojohn]

why is 2 phase - 240 volt - called single phase???

Because the zero crossing point is at the same point in time.
And each leg is in phase with the other, just equal and oposite voltage.

 

[electricman2]

my God, i just looked up the hundreds of old (and still going) threads on this subject and now realize that it would be better to just accept things the way they are and go on my merry way........

Yes, get the worms back in the can.

 

[big john]

The way I always looked at it:

A single phase 240 volt service only actually has one phase feeding the transformer primary. Hence, single phase.

But the real trick: Why is 120/208 single phase, which is actually two phases of a three phase system, called single phase? :grin: :roll:

-John

 

[chris kennedy]

Because the zero crossing point is at the same point in time.
And each leg is in phase with the other, just equal and oposite voltage.

I like this.

Are they named as per the primary?

A single primary will give the end user 120/240 with a grounded conductor. Yet you need 3 primarys to give the end user a 120/208 wye. Hence the label?

 

[djohns6]

Because the zero crossing point is at the same point in time.
And each leg is in phase with the other, just equal and oposite voltage.

Hmmm... I like that answer . My brother in law asked me that same question the other day . I tried to answer him but he got lost when I started talking about transformers , phase shift ,etc . He's a retired Chemical Engineer .
When HE starts talking about HIS work , I'm the one that get's lost . We usually stick to football and cars . :smile:

 

[hardworkingstiff]

Your best bet is to just accept it.

:grin: I laughed so hard I almost fell out of my chair!:grin:

 

[dbuckley]

But the real trick: Why is 120/208 single phase, which is actually two phases of a three phase system, called single phase? :grin: :roll:

Because it is.

I could explain why, but as its a secret, then I'd have to shoot you

 

[johnny watt]

Here?s my take on the reason why.
Lets say you were an experimenter during the infancy of electrical power generation.
You build an alternator with a single magnet and a single coil
You run that coil to a load using two wires.
You decide you need more power
You see that there is plenty of room for another coil so you add one at 180 degrees.
You realize that the two coils can be tied together to either double the voltage or current.
That way they can share the same wires going to the load.
You realize that the original two coil voltages can be reproduced with a transformer if necessary.
You also find that they cannot readily start a motor and are therefore not very usfull.
Since the voltages on these original two coils can be hooked up in phase you consider them to be in phase and don?t count them as separate phases.
Then you keep adding coils in different configurations and discover the rest of modern power generation.
Unaware that for the rest of time you have caused this confusion.
From this point forward all even phased systems will derive their angles by dividing into 180 but odd phased systems will get their angles by dividing into 360.

 

[coulter]

johnny
I don't know how much truth there is to it, but I certainly like it. Good job:smile:

carl

 

[glene77is]

dJohn6,

Agreed. I've tracked this Battle of the Phases through several threads.
It's interesting, but the (obviously) talented contributors are not speaking the same language.

When a Physicist and an Engineer and an Electrician get together
there will be three different Perspectives.
The truth is lost in a Semantic Battle.

In syllogistic logic, we call it a "Fallacy of Four Terms"
wherein the same word means something different,
depending on the perspective.

Glene77is

 

[mivey]

...In syllogistic logic, we call it a "Fallacy of Four Terms"
wherein the same word means something different...

Yeah, but how many meanings does "syllogistic" have? I had to go look that one up. :grin:

 

[dereckbc]

Because it is a single phase transformer with a center tap.

 

[Lxnxjxhx]

I think these worms are not easily going back into any can. . .