240v split phase correction

does split-phase have 2 sine waves in phase or out of phase with each other


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Thread Starter

Mac Rodriguez

Joined Mar 24, 2016
140
" A split-phase power system is one with multiple (in-phase) AC voltage sources connected in series, delivering power to loads at more than one voltage, with more than two wires "

I am having some definition or incorrect labeling problems with this text
My question is, does split-phase have 2 sine waves in phase or out of phase with each other. If they are out-of-phase, is it by 90 degrees or 180.

https://www.allaboutcircuits.com/textbook/alternating-current/chpt-10/single-phase-power-systems/
 

crutschow

Joined Mar 14, 2008
23,353
A split phase residential system in the USA consists of a 240V center-tap output from the mains transformer to the house.
The center-tap becomes the neutral, giving two 120V circuits to neutral, in addition to one 240V circuit between the two hot leads.
The two 120V circuits are thus 180° out-of-phase from each other.
 

Thread Starter

Mac Rodriguez

Joined Mar 24, 2016
140
A split phase residential system in the USA consists of a 240V center-tap output from the mains transformer to the house.
The center-tap becomes the neutral, giving two 120V circuits to neutral, in addition to one 240V circuit between the two hot leads.
The two 120V circuits are thus 180° out-of-phase from each other.

If you are correct (which I believe you are) then Allaboutcircuits.com made a mistake and should correct it.
 

Thread Starter

Mac Rodriguez

Joined Mar 24, 2016
140
That's the mistake? The 240V center-tap output from the mains transformer is the equivalent of two 120 vac transformer outputs in-phase and in-series.




Allaboutcircuits.com clearly states that split-phase is 2 sinewaves " in phase " with each other and they are not.
 

nsaspook

Joined Aug 27, 2009
6,280
If I were to put a oscilloscope on the panel in my North American residential house I would see 2 sine waves 180 degrees OUT OF PHASE from each other.
Yes, you would would if you reference the voltages from the center tap to each end but end to end the two voltages are in phase because of the transformer connections.
 

Thread Starter

Mac Rodriguez

Joined Mar 24, 2016
140
Yes, you would would if you reference the voltages from the center tap to each end but end to end the two voltages are in phase because of the transformer connections.
You can't put reference the voltage like that on a scope, can you.
 
Last edited:

crutschow

Joined Mar 14, 2008
23,353
but end to end the two voltages are in phase because of the transformer connections.
If you are measuring just two points than you are measuring the phase with respect to what?
Two points don't have a phase.

nsaspook said:
Yes, you would would if you reference the voltages from the center tap to each end but end to end the two voltages are in phase because of the transformer connections.

You can't put reference the voltage like that on a scope, can you.
Of course you can.
It is referenced to the neutral of the mains voltage.
 

Thread Starter

Mac Rodriguez

Joined Mar 24, 2016
140
If you are measuring just two points than you are measuring the phase with respect to what?
Two points don't have a phase.

nsaspook said:
Yes, you would would if you reference the voltages from the center tap to each end but end to end the two voltages are in phase because of the transformer connections.

Of course you can.
It is referenced to the neutral of the mains voltage.

You can't measure voltage PHASE TO PHASE on a scope like that.
You can only measure voltage PHASE TO NEUTRAL.
 

nsaspook

Joined Aug 27, 2009
6,280
If you are measuring just two points than you are measuring the phase with respect to what?
Two points don't have a phase.
I was talking about the equivalent of two transformer outputs in-phase and in-series to the center-tapped output like this diagram from the OP link.
Instead of a single 240 volt power supply, we use two 120 volt supplies (in phase with each other!) in series to produce 240 volts, then run a third wire to the connection point between the loads to handle the eventuality of one load opening. This is called a split-phase power system. Three smaller wires are still cheaper than the two wires needed with the simple parallel design, so we’re still ahead on efficiency. The astute observer will note that the neutral wire only has to carry the difference of current between the two loads back to the source. In the above case, with perfectly “balanced” loads consuming equal amounts of power, the neutral wire carries zero current.

The physical/wire construction of the 'upper and lower' secondary output transformer windings from the bottom connection , to center tap connection, to top connection.
 

Thread Starter

Mac Rodriguez

Joined Mar 24, 2016
140
I was talking about the equivalent of two transformer outputs in-phase and in-series to the center-tapped output like this diagram from the OP link.



The physical/wire construction of the 'upper and lower' secondary output transformer windings from the bottom connection , to center tap connection, to top connection.
So you are saying that if you took a transformer enclosure and had 1 primary winding @ 480v in it and shoved 2 secondary transformers in it each of which are for 120v and took 1 of the 2 wires coming of each transformer which was it's own neutral and tied them together and "tapped" off that connection to use at the connection point in the diagram between the 2 120v loads and somehow put my scope on each phase with no reference to the tied together neutral, I would see only 1 sinewave, is that right.
 

nsaspook

Joined Aug 27, 2009
6,280
You can't measure voltage PHASE TO PHASE on a scope like that.
You can only measure voltage PHASE TO NEUTRAL.
Sure you (carefully) can if the scope is isolated from neutral/ground with internal battery power or by using a isolation transformer. You need to separate the circuit (split-phase voltage from the center-tap) from the transformer voltage source physical component. If you were tasked with repairing (in an emergency like Harvey) a utility circuit using two bad utility step-down transformers transformers, each transformer had one end from the center tap to output secondary open but the opposite side from center-tap to output was good. How would you phase the output connections to make it deliver a correct 240VAC output to a split-phase circuit in a home?
 
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dendad

Joined Feb 20, 2016
3,009
Here in Oz, Ve have 240V mains power and you can get 3 phase power on if you need more power, like to run a big aircon or heating...
Just to confuse issues a bit, measuring from one phase to another gives 415V while phase to neutral is 240V.
Some bigger welders run on this "single phase" 415V to keep the mains current down.
I remember trying to explain this to an electrician in America on one of my visits and he just could not get it. I too did not then know about the 220V split phase you have there, so it was confusing both ways.
 

MaxHeadRoom

Joined Jul 18, 2013
19,042
Here in Oz, Ve have 240V mains power and you can get 3 phase power on if you need more power, like to run a big aircon or heating...
Just to confuse issues a bit, measuring from one phase to another gives 415V while phase to neutral is 240V.
.
Same as UK, whether using a phase to a phase, or a phase to the star neutral, they are each Single Phase.
Max.
 

dendad

Joined Feb 20, 2016
3,009
The two windings in the original question are in phase, like 2 batteries in series. But like in the battery example, if you measure from the centre tap you will get + and - voltages, or 2 phases 180 degrees different. But the windings ARE in phase. The confusion stems from the reference point being the centre, not one end.
For example, it is a common trick to add a low voltage secondary winding of a transformer either in phase or out of phase in series with the mains to increase or decrease the mains volts a bit.
 

nsaspook

Joined Aug 27, 2009
6,280
So you are saying that if you took a transformer enclosure and had 1 primary winding @ 480v in it and shoved 2 secondary transformers in it each of which are for 120v and took 1 of the 2 wires coming of each transformer which was it's own neutral and tied them together and "tapped" off that connection to use at the connection point in the diagram between the 2 120v loads and somehow put my scope on each phase with no reference to the tied together neutral, I would see only 1 sinewave, is that right.
If you used a Fluke 87 multimeter, what voltage would you get? It's the same as measuring voltage with a isolated Fluke 124 scope(meter).
 

dendad

Joined Feb 20, 2016
3,009
So you are saying that if you took a transformer enclosure and had 1 primary winding @ 480v in it and shoved 2 secondary transformers in it each of which are for 120v and took 1 of the 2 wires coming of each transformer which was it's own neutral and tied them together and "tapped" off that connection to use at the connection point in the diagram between the 2 120v loads and somehow put my scope on each phase with no reference to the tied together neutral, I would see only 1 sinewave, is that right.
It is a bit confusing, but if you had 2 transformers connected identically, with the "neutrals" together and measured across the "actives" you would have zero volts. Refer it back to batteries. Connect a couple of batteries together on the -Ve ends and measure across the +vs and you have zero. This is why parallel betteries work. Forget about AC for a bit and just look at dc as the phase relationship is the same in these examples. It gets a bit funny when you have 3 phase power, like the 240/415 example above.

I really should go to sleep. It is 1:30AM here. Good night all.
 
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