Why the loads on 2 Phases of a 3 Phase,220v,60Hz system are called Single phase?

[Anwar Pasha]

We find Air conditioning Units, motors, kitchen gadgets, washing machines are rated for 220V/1phase/60Hz but in domestic power supply system where the supply voltage is 220v/3p/60Hz, they are feeded with 2 phases but still they are called single phase instead of two Phase, while the same terminology changes when it becomes three phase!! Therefore my question is: "Why the loads on 2 Phases of a 3 Phase,220v,60Hz system are called Single phase?"

 

[Smart $]

We find Air conditioning Units, motors, kitchen gadgets, washing machines are rated for 220V/1phase/60Hz but in domestic power supply system where the supply voltage is 220v/3p/60Hz, they are feeded with 2 phases but still they are called single phase instead of two Phase, while the same terminology changes when it becomes three phase!! Therefore my question is: "Why the loads on 2 Phases of a 3 Phase,220v,60Hz system are called Single phase?"

Two source terminals, and two wires connected thereto, can only transfer one phase of AC power (i.e. there is only one voltage waveform, two if you count its polarity-inverted complement). What you refer to as two phases are actually two line conductors with their voltage phase determined using a third 3? source terminal.

 

[jumper]

"Why the loads on 2 Phases of a 3 Phase,220v,60Hz system are called Single phase?"

Because we have to call it something and 2 phase is already taken.

If someone follows what I think is conventional forms of writing I can easily figure the what the person is saying, such as:

120/240=single phase

120/208 = single phase from a 3 phase supply

240D/120= high leg delta 3 phase

208Y/120=3 phase

277/480= single phase from a 3 phase supply

480Y/277=3 phase

I do not know how corner grounded and ungrounded deltas are labeled.

 

[jim dungar]

"Why the loads on 2 Phases of a 3 Phase,220v,60Hz system are called Single phase?"

First, because you are calling things by the wrong name.

The conductors themselves are not phases.

Your question should be 'why the loads on 2 phase conductors of a 3-phase.... system are called single phase.

We often use slang terminology so commonly that we forget it is not technically correct. This slang usage often gets in the way of us being able to explain technical issues.

 

[Dennis Alwon]

If you have a few thousands hours to spare you can read this thread. Click Here I think this is what you are basically asking.

 

[Jraef]

If you have a few thousands hours to spare you can read this thread. Click Here I think this is what you are basically asking.

That thread has got to be an all time record...

Simplified answer to OP's question.

In 3 phase power you have 3 potential circuits; A-B, B-C and C-A right?

If you connect your load ONLY to the A-B circuit, how many is that?

 

[Anwar Pasha]

First, because you are calling things by the wrong name.

The conductors themselves are not phases.

Your question should be 'why the loads on 2 phase conductors of a 3-phase.... system are called single phase.

We often use slang terminology so commonly that we forget it is not technically correct. This slang usage often gets in the way of us being able to explain technical issues.

Thanks for rephrasing my question, if its 3 phase, 3 conductors will be rotating in magnetic space to produce emf, if a phase goes out, still there will be two phase in the system separated by 120 degrees, therefore, i would request you to kindly clarify"The conductors themselves are not phases"

 

[jumper]

Thanks for rephrasing my question, if its 3 phase, 3 conductors will be rotating in magnetic space to produce emf, if a phase goes out, still there will be two phase in the system separated by 120 degrees, therefore, i would request you to kindly clarify"The conductors themselves are not phases"

A conductor's voltage can have a phase angle, but a phase is not a physical identity that conducts electricity.

I think I got that right.

Edit: I meant to type entity, not identity.

 

[jim dungar]

"The conductors themselves are not phases"

Kind of like Jumper said.

A voltage is not a physical entity, like a conductor is.
Voltage exists between two points, not on 'a conductor'. If I ask you for the voltage on terminal 1, how do you respond?
Hopefully it is something like 'between terminal 1 and what'?

A 'phase' is also not a physical entity. It is a relationship between voltages.

Most of the large discussions concerning phases do not dispute the above two facts, rather their issue is usually defining the 'from where to where' of the voltages.

 

[Smart $]

Thanks for rephrasing my question, if its 3 phase, 3 conductors will be rotating in magnetic space to produce emf, if a phase goes out, still there will be two phase in the system separated by 120 degrees, therefore, i would request you to kindly clarify"The conductors themselves are not phases"

How many points does it take to measure 120?? Three.

How many degrees can you measure having only two points? Zero.

The load end of two wires can have only a single potential across their ends at any single instance in time, by offering only two points to measure.

You would need a third wire to measure any phasing relationship.

Even if a third wire is present, a load connected to two wires has only two connection points. Measuring voltage to the third wire is a phasing relationship that is not realized by the load.

 

[mivey]

How many points does it take to measure 120?? Three.

How many degrees can you measure having only two points? Zero.

The load end of two wires can have only a single potential across their ends at any single instance in time, by offering only two points to measure.

You would need a third wire to measure any phasing relationship.

Even if a third wire is present, a load connected to two wires has only two connection points. Measuring voltage to the third wire is a phasing relationship that is not realized by the load.

Pretty much sums it up IMO.

 

[charlie b]

That thread has got to be an all time record...

It is. It broke a record that stood for over six years. My one and only post in that thread was to mention the fact that it had taken over the record. That post of mine was at least 100 posts ago.