why is it called 1 phase when its 110/220v. but 3 phase when its 3 "hots"

[mivey]

If there's a neutral.

You guys are relentless. Must ... resist ... too late: :grin:

The historically-labled two phase can have 3, 4, or 5 wires. The three & five wire cases have neutrals.

As for the rest:
In the general definition of a multiphase system, the number of phases for the system is the number of equal magnitude and equal frequency waveforms with different angles. In the canonical definition of a multi-phase system, we get the added constraint that a n-phase system will have n waveforms evenly displaced by 360/n degrees.

The historically-labeled two phase system with a 90 degree separation is really a subset of a canonical four-phase system but also meets the general definition of a two-phase system (as would separations of 91 or 92 or 93 or 94 or ... degrees).

We have adopted conventions for naming the systems we use. The naming conventions are not consistent, but they are what they are. To avoid confusion, we stick with the naming conventions everyone has become accustomed to.

Note that most of the time these naming conventions are based on how the phases were being used instead of using the general or canonical definition.

 

[pfalcon]

The answer is simple if y'all would stop thinking like electricians.

Single phase power is single phase cause it only powers single phase devices.
Three phase power is three phase cause it can power three phase devices.

Sure you can cloud the issue. A dryer is typically two single phase devices built into one. The drying circuits are at the higher voltage and the controls are at the lower voltage. Point being that each of those circuits are still single phase.

And sure you can ignore two phases of a three phase system. Point is those other two phases are present to run three phase devices if you want them.

 

[Smart $]

... The three & five wire cases have neutrals.

...

Afraid not... at least not technically. What you are calling a neutral on the 3-wire version is a common, as in 4-wire version with two wires connected.

 

[TwinCitySparky]

Only 600 more responses to go.

 

[mivey]

Afraid not... at least not technically. What you are calling a neutral on the 3-wire version is a common, as in 4-wire version with two wires connected.

If you are going to be picky, at least get it right. :grin:

You are technically 1/2 right. But I am afraid it is so for the 4-wire system...at least technically.

A neutral point is defined by the ANSI/IEEE Standard 100 as: "the neutral point of a system is that point which has the same potential as the point of junction of a group of equal non-reactive resistances if connected at their free ends to the appropriate main terminals or lines of the system."

So what we call the neutral on a 120/208 3-wire network service is not really a neutral point either. And what we call the neutral on a 120/240 delta service is not the neutral point for the 3-phase portion but only for the single phase portion of the service.

 

[iwire]

Only 600 more responses to go.

:grin::grin::grin::grin:

You guys are relentless. Must ... resist ... too late: :grin:

You are hooked, addicted, the monkey is on your back and you can't shake it off. :grin:

 

[mivey]

:grin::grin::grin::grin:

You are hooked, addicted, the monkey is on your back and you can't shake it off. :grin:

Oh yeah. That's what I like to see. Two posts in a row. Ummmmm. :grin:

 

[iwire]

Oh yeah. That's what I like to see. Two posts in a row. Ummmmm. :grin:

I only see one:grin:

 

[mivey]

I only see one:grin:

I was living vicariously through you. Plus, I was Jonesing to read another thread. :grin:

 

[e57]

The answer is simple if y'all would stop thinking like electricians.

Single phase power is single phase cause it only powers single phase devices.
Three phase power is three phase cause it can power three phase devices.

Sure you can cloud the issue. A dryer is typically two single phase devices built into one. The drying circuits are at the higher voltage and the controls are at the lower voltage. Point being that each of those circuits are still single phase.

And sure you can ignore two phases of a three phase system. Point is those other two phases are present to run three phase devices if you want them.

You can also ignore just 1 of 3 phases and power single phase devices - from two phases of wye or delta...

Blame Tesla....

 

[quogueelectric]

You can also ignore just 1 of 3 phases and power single phase devices - from two phases of wye or delta...

Blame Tesla....

Yes EVERYONE blamed poor Tesla.

 

[pfalcon]

Yes EVERYONE blamed poor Tesla.

Wait until the mandate a Faraday cage over your PPE clothing. Then you can blame Faraday too! :grin:

 

[mivey]

Wait until the mandate a Faraday cage over your PPE clothing. Then you can blame Faraday too! :grin:

Remote controlled bots will be the future. No real skin will have to come close to those mischievous and dangerous little electrons.

 

[LarryFine]

Remote controlled bots will be the future. No real skin will have to come close to those mischievous and dangerous little electrons.

Nanites!

 

[dakotared]

Why is120/240 called single phase

Why is120/240 called single phase

Look a the supplying transformer. Primary is tapped on one leg of three-phase and secondary coil is grounded in the middle of the coil, forming the grounded conductor(neutral). the two end to ground=120 volts, and then across ='s 120 +120='s 240... stillderived from one leg of a three-phase primary....hot's are usually referred to as X1 and X2. The Neutral is referred to as O....

 

[StevenRayWebb]

Single phase, 2 or 3 phase

Single phase, 2 or 3 phase

The simple answer is:
The reference to "phase" is short for "phase angle differrence".
Describing the 60 Cycle/Second waveform timing of the voltage or current between sources. In a single loop with 2 wires the waveform phase angle difference will always be the same. Add more wires to the loop, a phase angle difference is possible.
With 4 wires it is possible to have a 2 phase system.
The RMS Voltage between wires is dependent on the phase angle difference between them and how they are connected.

 

[Don Randall]

Polarities

Polarities

When dealing with US electricity, Single phase for residential and commercial should be considered "Split Phase", where 1 single phase winding in the transformer is tapped [or split] in the middle and grounded - so in reality you still have 1 winding - making it 1 single phase. 2 phase is totally different and should not be considered the same.

Heres a good diagram:

Looking closer at it, the polarity is incorrect, but the single winding and voltages are correct. For this topic, it should suffice.

~Matt

If the polarities are incorrect, (I wouldn't say they are), what do you think they should be?
Don

 

[Besoeker]

If the polarities are incorrect, (I wouldn't say they are), what do you think they should be?
Don

Surely the symbols "+" and "-" are inappropriate for an alternating voltage?

Anyway, back on topic......
Someone on this thread back in the mists of time mentioned zero crossing as a means of differentiating between the number of phases.
If you take a centre*-tapped supply and measure the voltages end to end or either end to the centre, the voltage crosses zero at the same time - maybe going in opposite directions, but at the same time nevertheless.
In a three-phase system there are three different zero crossing points.
QED.

*This is not a typo or a misspelling. It's British English.

 

[Don Randall]

Surely the symbols "+" and "-" are inappropriate for an alternating voltage?

Not at all inapproiate. It is used to indicate circuit conditions at a certain point in time, thus showing the relationship of various parts of the circuit to each other. Although, (in the U.S.A.) , the polarities reverse 120 times per second. Don

 

[Besoeker]

Not at all inapproiate. It is used to indicate circuit conditions at a certain point in time, thus showing the relationship of various parts of the circuit to each other.

The dots do that by indicating winding starts.