Hey all,
The electrical input from the electric company is single phase. No matter if it is 110V, 240V, 440V, or ten billion Volts. The wiring of a device is what utilizes phasing.
Please explain this to your constituents.
Dan

 

If it is 240AC with a neutral, it's not.

You are also talking US code, different parts of the world do things differently, different frequencies, amplitudes.

But I would be interested in finding out how L1 to Neutral is 120VAC, L2 to Neutral is 120VAC, and L1 and L2 have 240V.

 

Hey Bill,
Nope. Delivery is always single phase.
Dan

 

OK, answer my question. Merely stating something is so doesn't make it so. The power company actually uses 3 phase, but I know this isn't residential.

 

Bill,
Good enough is the enemy of the best, your saying.
You are not only incorrect, but perpetuating a misnomer. This is what I am trying to correct. The input is single phase, the output is dual to multi- phase.
Dan

 

The input to my power transformer (which far away from my house), is single phase. What comes into my home is split phase. The power transformer is in front of my meter.

Widipedia also referes to it as 3-wire, single-phase, mid-point neutral. Refering to it as two phase is incorrect, but we still have two hot lines 180° as I described in post #2.

 

Not really sure what you are saying.

The company's electricity cables, buried in my road are three phase and neutral (i.e.four core) with a metal armour sheath which is used as earth. Other earthing arrangements are sometimes used.

I can choose to buy a single phase or a three phase supply from the company. It then provides a connection to one of the phase conductors and neutral or all three and neutral.

Only heavy power users will choose a three phase supply, eg Studio T is on a single phase but the Hospital just up the road receives three phase.

So the power company balances the distribution of the users on each phase, along with the street lights.

 

I don't know how power is transmitted in US but in Cyprus it is transmitted with the same way as Studiot described briefly.
If they use single phase transmittion in US and then split it to two phases with 180 degrees phase shift (for houses) how one gets three phase power? I think they still carry the power with 3 phase systems because it is more efficient and at the end they split one phase of it into two.

 

I don't know how power is transmitted in US but in Cyprus it is transmitted with the same way as Studiot described briefly.
If they use single phase transmittion in US and then split it to two phases with 180 degrees phase shift (for houses) how one gets three phase power? I think they still carry the power with 3 phase systems because it is more efficient and at the end they split one phase of it into two.

3 Phase in the USA is industrial. I suppose if you wanted it in your home they would cable it (for a cost). Basically the line tap, be it a pole transformer or ground unit like mine (which is great!) takes a single phase signal and splits it, similar to what I showed in an earlier post (and was dismissed by another user). The picture I drew of the transformer and Wikipedia's are pretty similar though.

http://forum.allaboutcircuits.com/showthread.php?t=17469

The reason is we do have appliances in the USA that require 240VAC, this allows for both 120VAC and 240VAC.

I suspect that they balance the loads on the 3 phases between neighborhoods. In the factory I used to work at we just tapped into one of the 3 phases for a 120VAC leg.

 

Hey Mik,
Didn't know you are in Cyprus. I do not know how single phase is turned into three phase. The transformer is how the electricians tell it. What I am saying is, if only two wires come in, where does the three phase come from? I have three phase motors in my home, yet, only two wires coming in.
The devices, say a dryer, its' motor is wired for three phase. My radial arm saw is three phase, but I plug it into a three pronged plug. I do not see here at AAC answers about AC line input, and some ask those questions. Since I deal with AC on a regular basis, the input phasing is important. I am hoping someone here will explain how it works.
As always thanks for the response, you are one or the best.
Dan

 

It may say 3 phase, but it's not. You can't convert between eacy other, though you can use a leg for 120VAC. 3 Phase 207VAC can make 3 separate legs of 120VAC, or 2 legs can substitute for 220VAC (it is a pretty common alternative).

If it were easy the power company wouldn't use 3 wires on their high tension lines, but convert at the substation. A general rule is you can always use one phase of a multiple phase line.

 

Bill,
Then please explain how three phase comes out of 2, 3, 4, or fifty wires.
I have three phase wiring in my home, yet only two wires coming in. Explain so we all can teach.
Dan

 

If you have 2 wires (L1 and L2) then it isn't 3 phase. 3 phase requires 3 wires, and in addition a neutral (4 wires). 3 Phase is just what it sounds like, 3 legs out of phase 120° with each other, hence 3 wires. I'm willing to bet you have split phase, which is the standard in the USA. There are motors and whatnot that actually require all 3 phases, but not for home use. I've wired industrial equipment to 2 phases on a 3 phase system, from the equipments point of view it was single phase (except both wires were hot, but to a transformer that doesn't matter).

As to your home, I'm not psychic. Have you read the Wikipedia article (out of curiousity), or the AAC book?

To tell if you have phasing other than 180° the voltages do not add linearly. The difference between 2 phases is 207VAC, while the individual legs are 120VAC. With the split phase system they are linear, the two legs at 120VAC add to 240VAC.

 

I agree with Bill. At your house you have a two phase system (in US which is actually a single phase separated into two phases for practical reasons). You have 3 wires coming in your house, two hot wires for the phases and one neutral wire. However this is not 3 phase power. The voltage between the two hot wires is 240V rms and between the neutral and one of the two hot wires is 120V rms. Also, you will see a 4th wire which is the ground wire. If you had 3 phase power you would see 3 hot wires (phases), one neutral wire and one ground wire. If you need 3 phase power at home you have to ask the electric supplier company to install it in your house (if they decide that you need it).

 

Dan,

Read this: http://www.allaboutcircuits.com/vol_2/chpt_10/2.html

It might help clear up your confusion.

If you have a three phase outlet in your garage or shop, but only split phase at your main panel, then you have a gizmo called a "phase converter" somewhere in the mix.

 

Note in particular the following extract, which couldn't be more true.

One question remains to be answered: how in the world do we get three AC voltage sources whose phase angles are exactly 120o apart? Obviously we can't center-tap a transformer or alternator winding like we did in the split-phase system, since that can only give us voltage waveforms that are either in phase or 180o out of phase.........

........The best way to get the phase shifts we're looking for is to generate it at the source:

which of these connectors does your '3phase' equipment have?

http://en.wikipedia.org/wiki/NEMA_connector

 

A phase converter is a 3 phase inverter, it generates the power signals completely independently of the power company.

 

Okay guys,
One more time. Why do I have three phase motors from a single phase input? The transformer to my house, or business has two wires coming in. Three out. Plus ground. And I have three phase motors in my A/C, etc...
Why? Because the motors are wired for three phase. 120 degrees. Not 180 degrees.
Dan

 

Okay guys,
One more time.

Not that anyone is keeping count...

Why do I have three phase motors from a single phase input?

We have not established that such is the case. Why do you assume your motors are three phase?

The transformer to my house, or business has two wires coming in. Three out. Plus ground.

You describe a standard split-phase arrangement. 240 single phase in. 120/120 split phase with neutral out. Plus ground.

And I have three phase motors in my A/C, etc...

Please provide evidence of this.

 

Thingmaker,
With all due respect, read the second paragraph again. Not only do new guys post here on this forum for electronic circuits, but also for electrical circuits. And this idea that there are homes, or businesses "wired" in three phase is just nonsense. The motors, or devices are wired for three phase. As I have been stating from the beginning. I'm not good at pictures, but I will draw you one in paint, if necessary.
Dan
P.S. I am not a licensed electrician. But I can look up in the sky and say which is a star, and which is a planet.