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Help running this 220v machine in my house

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mjkuwp:

--- Quote from: administr4tor on January 09, 2023, 07:57:55 pm ---how will it work? the AC in those NEMA are two single phase 120v right? and the AC the device would work on single 230v AC.

....

--- End quote ---

no, there are not really two phases in a USA house, it is split phase.  I am not 100% certain of what the nominal voltage is but in my house (USA) I often measure 125VAC.   We have two sides to our electrical box and various circuits are taken from one side of the box or the other at random (or maybe somebody plans it).  if I were to measure voltage between the two Hot wires of circuits taken from opposite sides of the main box, then I will get 240VAC or maybe even 250VAC. 

https://en.wikipedia.org/wiki/Split-phase_electric_power

james_s:

--- Quote from: mjkuwp on January 10, 2023, 08:07:59 pm ---no, there are not really two phases in a USA house, it is split phase.  I am not 100% certain of what the nominal voltage is but in my house (USA) I often measure 125VAC.   We have two sides to our electrical box and various circuits are taken from one side of the box or the other at random (or maybe somebody plans it).  if I were to measure voltage between the two Hot wires of circuits taken from opposite sides of the main box, then I will get 240VAC or maybe even 250VAC. 

https://en.wikipedia.org/wiki/Split-phase_electric_power

--- End quote ---

The nominal voltage in the USA has varied over the years but for at least the past several decades it has been 120/240V. I forget what the allowable tolerance percentage is, but 125V is near the upper end IIRC and back in the incandescent era that would result in a significant lifespan reduction but increased efficiency of the bulbs.

To sum up split phase power in a nutshell, houses are fed by a 240V transformer with a center tapped secondary and this center tap is connected to ground and neutral. This gives you 120V from either side to ground and 240V between them.

J-R:
IMHO, whether you call 240V or even 208V single phase or two/dual phase really should come down to whether the neutral is part of the load's circuit or not.

Three phase grid/commercial is "blatantly" three phase because there are three separate AC waveforms on three separate wires, 120 degrees out of "phase".  We can easily view this because we can pick an independent reference point when making our voltage over time graphs.  This definition hasn't changed since the 1800s.

For residential, we center-tap the secondary of the grid's step-down transformer to split 240V into two 120V outputs, each 180 degrees from each other.  If we graph our voltage over time for this using neutral (& ground to some extent) as our reference point, we see the SAME sine waves as the three phase, with the ONLY difference being that there are only two phases 180 degrees from each other, instead of three phases at 120 degrees from each other.

So while it's true that for N.A. residential there is only a single grid phase feeding your house transformer, we are essentially creating another "phase" by splitting the transformer.

Older electrical codes allowed 240V outlets with NO neutral.  In this case, there can be only one phase as far as the load is concerned, because it can't use ground as part of the circuit.  When graphing voltage over time, there is only a single sine waveform visible.
However, if I come along and reference ground with my two test equipment probes, I will see two waveforms, one on each wire, 180 degrees from each other, AKA two phase.
Newer electrical codes add a neutral back in to the 240V outlets, so again in this case you have two phases/waveforms.  There is just no getting around it.

james_s:

--- Quote from: J-R on January 11, 2023, 02:38:21 am ---IMHO, whether you call 240V or even 208V single phase or two/dual phase really should come down to whether the neutral is part of the load's circuit or not.

Three phase grid/commercial is "blatantly" three phase because there are three separate AC waveforms on three separate wires, 120 degrees out of "phase".  We can easily view this because we can pick an independent reference point when making our voltage over time graphs.  This definition hasn't changed since the 1800s.

For residential, we center-tap the secondary of the grid's step-down transformer to split 240V into two 120V outputs, each 180 degrees from each other.  If we graph our voltage over time for this using neutral (& ground to some extent) as our reference point, we see the SAME sine waves as the three phase, with the ONLY difference being that there are only two phases 180 degrees from each other, instead of three phases at 120 degrees from each other.

So while it's true that for N.A. residential there is only a single grid phase feeding your house transformer, we are essentially creating another "phase" by splitting the transformer.

Older electrical codes allowed 240V outlets with NO neutral.  In this case, there can be only one phase as far as the load is concerned, because it can't use ground as part of the circuit.  When graphing voltage over time, there is only a single sine waveform visible.
However, if I come along and reference ground with my two test equipment probes, I will see two waveforms, one on each wire, 180 degrees from each other, AKA two phase.
Newer electrical codes add a neutral back in to the 240V outlets, so again in this case you have two phases/waveforms.  There is just no getting around it.

--- End quote ---


It's still called single phase power, a single split phase, not 2 phase. It's derived from one of the three phases that are present outside on the utility pole, though often a residential neighborhood will only have one phase run to it off of the arterial.

As far as I know you're still allowed to have 240V outlets without neutral. The change to the code mandates a neutral if you have any 120V loads on it. For example electric ranges used to typically use ground as neutral for the oven light and the clock and such, clothes dryers did the same with the interior light and timer. Modern dryers and ranges need a 4 prong plug and ground is used ONLY as a safety feature.

J-R:
You can call it what you want, but it's still two phases.

208V created from two grid phases is called single phase, for the reason I stated, which is because there is no neutral.

So it has nothing to do with whether the grid is providing you one, two or three phases.

Ultimately, Sparky can't have it both ways, either 208V is two phase, and residential is single phase because of the grid connection, or 208V is single phase and residential is two phase because of the output waveforms present.

I don't see the logic in referencing some invisible upstream supply when talking about what is sitting in front of you.  You have what you have...

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