I think I see where some of the confusion is, looking at the batteries in the drawing they are facing the same way, but compared to ground they are reversed. If the same polarity was connected to ground then there would not be any voltage out.

First, I hope I'm not stepping on any toes here; I respect your input and I think you could wire a house. I used to wire them for a living and I know what to connect to where, believe me. As I said, I think the whole problem we're having is a difference in definitions of two phase rather than refering to this situation as single phase with two legs of the secondary of a single phase transformer.

As you know, the power company sends our localities 3 phase voltage over three wires. These voltages are 120 degrees apart. Industrial areas get all phases stepped down through a bank of three xformers so they can run 3 phase motors. But any particular area will get only one phase. Look at the xformer that feeds your house. Above it you will see one small diameter wire.

This feeds one lead of the primary of your xformer, the other is connected to a grounded wire. At the secondary we have a center-tapped coil. It is all wound in the same direction and between its outer legs is 240 volts. The center tap is connected to earth ground.

Now, with respect to this transformer it is polarized as per your battery drawing. Notice the batteries are in series, not in parallel. Also, the xformer diagram should be marked with the same polarizations as per your battery drawing. Your phase drawing is incorrect. From top to bottom it should be + - + -. These are in series and in phase with each other and therefore 120 volts adds to 240 when you connect them to an appliance. The grounded center tap -- neutral -- is not a part of the circuit, except short circuit protection for the appliance casing.

This whole discussion came about because I objected to Sgt W's calling this two phase (180 degrees apart) which it is not. It is single phase and the correction on your drawing so that the voltages are in phase, not 180 degrees apart is needed.

But you're looking at the case inside the house where the center tap is indeed grounded and you get two legs of 120 volts each. From the transformer's point of view you're mearly making a connection between its legs, not its centertap, and therefore getting the whole 240 volts across the entire secondary winding. This means it is still single phase, not 2-phase. To get two phase the power company would have to deliver two, not one, of its feeders.

 

I don't think so. I used the centertap for reference, but the fact remain that two signals in phase on two wires will have 0 volts between them. The out of phase is where the 240VAC is coming from. This isn't definition, it is fact, as spoken by 5 or more experience types on this thread.

Two identical 120VAC signals will work just fine to neutral, but have 0 volts between them, as if they were the same wire, even though they aren't directly connected. We are talking potentials here.

As far as I am concerned this is off topic to the OP, so I will not be responding any more in this thread. I would be glad to continue the conversation in another thread.

 

Good Evening, Paul

 

This whole discussion came about because I objected to Sgt W's calling this two phase (180 degrees apart) which it is not. It is single phase and the correction on your drawing so that the voltages are in phase, not 180 degrees apart is needed.

The appropriate term is "split phase," as it does not invoke these "poTAYto vs pohTAHto" misunderstandings. Phase angle requires a reference. Depending on which reference is chosen one can have one phase or two in a North American home. The electrons don't care what we choose as a reference.

 

Paul;

I can tell you know your stuff but you have got your mind mixed up on this standard US home AC wiring standard, and it's not as complex as it may seem. Forget about the primary wiring to a home service transformer and just consider the center tapped secondary winding.

The total secondary winding is a single phase 240vac winding with a center tapped connection called neutral that is also wired to ground at the service panel. There is indeed two phases, L1 & L2 of 120vac that are distributed in alternate rows on a standard breaker box so that each adjacent 120vac breaker gets it's input voltage from the opposite phase and the neutral buss.

Any 240vac breaker will be double thick and thus gets both input phases but no connection to neutral. These two 120v 'buses', L1 and L2 do indeed have a 180 degrees phase shift between them. One obtains 240 volt service by wiring the load directly between L1 and L2 (after the circuit breaker of course) with no need for a neutral wire and is used for the high current device in a home like dryers, ovens, etc. A safety ground wire is also ran for 240v devices but again no neutral wire is used on 240volt. The two 120volt buses use neutral for their return current path and thus see half the voltage as the total secondary voltage. If the two phases of 120vac (L1 & L2) had 0 phase difference then there would be no way that 240vac would be seen. The key is this 180 degree phase difference is it's + & - 90 degrees relative to the center tap.

A simple experiment would prove my case if one built a long extension cord with male connectors on the both ends (yea, I know not a safe thing to have laying around!) and say plug one end at a receptacle in one room and start plugging the other end to random plugs around the house. You should find that you would be tripping breakers on around 50% of the outlets and not tripping breakers on the other 50%. Why, because have the 120vac outlets are wired to L1 and the other half L2 and wiring two hot L1 together causes no current to flow and hooking a L1 and L2 hot together is just like applying a short across the 240volt secondary winding.

Maybe it's just simpler to use a dual channel scope at the breaker box and put channel one on L1 and channel 2 on L2 and the scopes ground reference to AC neutral, you will see the 180 phase difference on the scope.

This is not unlike how a bi-polar DC rectifier is wired to a center tapped secondary winding. The center tap becomes the circuit common and the diode DC terminals output a positive and negative voltage referenced to the center tapped common. However if you measure from the + to the - output of the rectifier you read double the DC voltage on either the + or - value. Same principal same method.

So the correct name of this AC service is split phase not two phase, but that doesn't change the fact that the L1 and L2 120 volt buses have a phase difference relative to the neutral connection.

Lefty

 

Sorry, studiot, I confused you with a poster tagged awediot. CARM is another forum -- Christian Apologetics Research Ministry. You might want to try it. You'll find great discussions not matter whether you are a Christian or of another religion. One group of threads is called Secular. Mostly atheists. Very educational.

 

PRS, ... The addition you refer to happens when the voltages are at a single point.

Addition happens when inductors are in series and your measuring the voltage across both. This is the case at the secondary of the xformer serving your house. Actually it is but one winding with a center tap. 240 volts shows up across the entire winding. But when it is center-tapped and grounded we get 120 volts from the high leg L1 and the low leg L2 with respect to the center tap.

What Bill is saying is that if two points (not one ) are at the same voltage there is no voltage difference between them.

I realize this. But you need to remember that the xformer has 240 volts between its legs L1 and L2. When you connect an induction motor between L1 and L2 it is 240 volts single phase. Also when you connect 120 volt moters or appliances between one leg and ground it is 120 volts single phase. My argument is that residential wiring is single phase, not two phase. I understand the term split phase, but it's not the same as two phase. The electrical supply to your town is 3 phase -- three wires with 120 degrees of phase shift between each. You get only one of the phases for your home, thus residential wiring is single phase.

 

The appropriate term is "split phase," as it does not invoke these "poTAYto vs pohTAHto" misunderstandings.

Excellent analogy. I am (we are?) nit picking the definition of two phase.

Phase angle requires a reference. Depending on which reference is chosen one can have one phase or two in a North American home. The electrons don't care what we choose as a reference.

Agreed.

 

Paul; I can tell you know your stuff but you have got your mind mixed up on this standard US home AC wiring standard, and it's not as complex as it may seem. Forget about the primary wiring to a home service transformer and just consider the center tapped secondary winding.

Ah, but that is where you force your own definition on me!

The total secondary winding is a single phase 240vac winding with a center tapped connection called neutral that is also wired to ground at the service panel. There is indeed two phases, L1 & L2 of 120vac that are distributed in alternate rows on a standard breaker box so that each adjacent 120vac breaker gets it's input voltage from the opposite phase and the neutral buss.

Yes.

Any 240vac breaker will be double thick and thus gets both input phases but no connection to neutral. These two 120v 'buses', L1 and L2 do indeed have a 180 degrees phase shift between them.

With respect to the center tap and ground.

One obtains 240 volt service by wiring the load directly between L1 and L2 (after the circuit breaker of course) with no need for a neutral wire and is used for the high current device in a home like dryers, ovens, etc. A safety ground wire is also ran for 240v devices but again no neutral wire is used on 240volt.

Yes.

The two 120volt buses use neutral for their return current path and thus see half the voltage as the total secondary voltage. If the two phases of 120vac (L1 & L2) had 0 phase difference then there would be no way that 240vac would be seen. The key is this 180 degree phase difference is it's + & - 90 degrees relative to the center tap.

The return path for L1 is L2 and the return path for L2 is L1. Remember that when you are connected between L1 and L2 (and the neutral is not used) you are connected directly across the whole xformer secondary winding.

A simple experiment would prove my case if one built a long extension cord with male connectors on the both ends (yea, I know not a safe thing to have laying around!) and say plug one end at a receptacle in one room and start plugging the other end to random plugs around the house.

I actually did made a two plug extention cord and used it in my own home one winter when a whole circuit went dead. Crazy? It worked!

You should find that you would be tripping breakers on around 50% of the outlets and not tripping breakers on the other 50%. Why, because have the 120vac outlets are wired to L1 and the other half L2 and wiring two hot L1 together causes no current to flow and hooking a L1 and L2 hot together is just like applying a short across the 240volt secondary winding.

I understand perfectly. I used a meter before I did it.

Maybe it's just simpler to use a dual channel scope at the breaker box and put channel one on L1 and channel 2 on L2 and the scopes ground reference to AC neutral, you will see the 180 phase difference on the scope.

Yes, I know this. I am not argueing that L1 is not 180 degrees out of phase with L2 with respect to ground. My argument is in the definition of two phase. Residential wiring is single phase.

This is not unlike how a bi-polar DC rectifier is wired to a center tapped secondary winding. The center tap becomes the circuit common and the diode DC terminals output a positive and negative voltage referenced to the center tapped common. However if you measure from the + to the - output of the rectifier you read double the DC voltage on either the + or - value. Same principal same method.

I understand. I'm into electronics, too.

So the correct name of this AC service is split phase not two phase, but that doesn't change the fact that the L1 and L2 120 volt buses have a phase difference relative to the neutral connection. Lefty

Nor does it change the fact that residential is single phase. The 120 volt system is single phase and drives induction motors which require single phase. The 240 volt system is also single phase and drives single phase induction motors.

 

Bill, I think it's just a nit pickin argument of mine over definitions. Sorry if I offended you.

 

Good evening, studiot.

 

Happy New Year, Paul

Perhaps you will address my point in post#17 in 2009?

 

Happy New Year to all.
And yes, your house is wired single phase 240V. 120V from L1 to neutral (or ground) 240v L1to L2.
Split-phase, 2-phase, three-phase, million-phase makes no difference. The phase wiring is in the device, or appliance, not in the delivered electricity to the home.
Dan

 

Happy New Year to everyone, and may your phases, whether single, split, two, three, or more, be complete and regulated.

 

Happy New Year, Paul

Perhaps you will address my point in post#17 in 2009?

I thought I answered you. I confused your name, studiot, with a poster at another forum named awediot. I have to add here that I don't understand these names.

At any rate I am an avid poster at a forum called CARM -- Christian Apologetics Research Ministries. It is a very lively place with plenty of atheists and folks of different denominations, different religions, to offer lots of counterpoint. I mainly post to the secular types on the topic of science, but I am a YEC -- Young Earth Creationist.

 

Happy New Year, SgtWookie. May the phases be with you!

 

I thought I answered you. I confused your name, studiot, with a poster at another forum named awediot. I have to add here that I don't understand these names.

At any rate I am an avid poster at a forum called CARM -- Christian Apologetics Research Ministries. It is a very lively place with plenty of atheists and folks of different denominations, different religions, to offer lots of counterpoint. I mainly post to the secular types on the topic of science, but I am a YEC -- Young Earth Creationist.

Now you have me totally confused.

I pointed out that Bill Marsden( and others) were describing a different physical situation from your own description.

You were both correct about your own particular setup.

My comment was meant to be helpful.

 

amasing how a simple question can creat such a discushion

 

out of phase the power doubles get some paper and draw these sinewave and then you will see. In the usa 240v ac is brought to the house but only one phase is used so 120 v ac. the ground wire is for safety it is just a way to insure that if excessive current flow the house does not rise to a killing potential. GFI plugs sense this current and trip themselves off. also if hit by lightning the house does not rise to a killing potential. All power sub-station are actually grounded with heavy wire to prevent the actually to rise.

 

Sorry, I must have miscounted the posts and picked the wrong one. If I remember right you made a point about residential supplies being split phase. If that doesn't mean 2 phase I agree. Two phase is specific. The only motor that I know of that is 2 phase is a servo. It is fed by two lines 90 degrees apart and usually the frequency is about 15 kHz. A signal varies this frequency causing an actuator to rotate with respect to frequency.