# 3-wire electrical circuit serving both 110 and 220V loads?

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• posted on April 14, 2014, 10:43 pm
Sorta...
I have a degree in Physics and retired as an EE after 20+ years.
Watts is the value in power if it were a resistive load. VA is the voltage times the current (and ignoring the phase angle between them) Which gives a completely different wattage for a reactive load like a motor.
ELI the ICE man. Voltage leads current (in time) in inductive (coil) circuits. Current (I) leads Voltage in a capacitive circuit - starting coil with cap. Cap larger than coil in reactive values. XL == ac resistance XC == ac resistance.
Martin
On 4/13/2014 10:53 PM, snipped-for-privacy@gmail.com wrote:

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• posted on April 18, 2014, 2:20 pm
On 4/13/14 9:53 PM, snipped-for-privacy@gmail.com wrote:

One problem I see is you are wiring a 110V outlet on a 30A circuit. That is fine, but you need to get an outlet rated for 30A. The typical 110V duplex is 20A max (NEMA 5-20), Your outlets will need to be NEMA 5-30 (which may have issues with your 110V plugs on your tools).
-Bruce

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• posted on April 14, 2014, 3:54 am
On Thursday, December 23, 2004 10:59:07 AM UTC-8, Keith Carlson wrote:

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• posted on April 14, 2014, 4:25 am
In the U.S. I don't believe there is any such thing. Household supply is obtained from a single phase of a three phase system. For all intents and purposes, when the power grid appears in your neighborhood, forget about two of those phases. You will never be involved with them. Only single phase is getting into your house.
The single phase current is transformed from a fairly high voltage off the feeders to 240V from the output of a center tapped transformer up on the pole. With regard to that 240V, there is no neutral. The 240V comes from the two secondaries of the transformer. And there is no + or -. This is AC, not DC. It is 240V across the two poles.
Our well known 120V supply comes, as you know, from one hot leg and the center tap of the transformer. Either hot leg will work.
Here is the most important thing: ALL of this; the 240V, and each 120V is developed from the same single phase of the three phase system. It is single phase power. There is no "two phase" power.

There is no "two phase" power. The two legs or poles are 180° out of phase, as you say, because they come off the opposite legs of the secondary of the transformer. They are NOT two phases of the three phase system. It is single phase. All of the current in your house comes from the same, SINGLE phase of the three phase system.

Yes and no, but I will leave that discussion to those with experience with it. I have none.

1

It IS single phase. There's no "thinking" about it.

Sigh. Yes, you have stated a tautology.
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• posted on April 14, 2014, 4:25 am
In the U.S. I don't believe there is any such thing. Household supply is obtained from a single phase of a three phase system. For all intents and purposes, when the power grid appears in your neighborhood, forget about two of those phases. You will never be involved with them. Only single phase is getting into your house.
The single phase current is transformed from a fairly high voltage off the feeders to 240V from the output of a center tapped transformer up on the pole. With regard to that 240V, there is no neutral. The 240V comes from the two secondaries of the transformer. And there is no + or -. This is AC, not DC. It is 240V across the two poles.
Our well known 120V supply comes, as you know, from one hot leg and the center tap of the transformer. Either hot leg will work.
Here is the most important thing: ALL of this; the 240V, and each 120V is developed from the same single phase of the three phase system. It is single phase power. There is no "two phase" power.

There is no "two phase" power. The two legs or poles are 180° out of phase, as you say, because they come off the opposite legs of the secondary of the transformer. They are NOT two phases of the three phase system. It is single phase. All of the current in your house comes from the same, SINGLE phase of the three phase system.

Yes and no, but I will leave that discussion to those with experience with it. I have none.

1

It IS single phase. There's no "thinking" about it.

Sigh. Yes, you have stated a tautology.
- -
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• posted on April 14, 2014, 4:26 am
On Thursday, December 23, 2004 10:59:07 AM UTC-8, Keith Carlson wrote:

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• posted on April 14, 2014, 4:34 am
On 4/13/14, 11:00 PM, Leon wrote:

He wanted to reply then, but it took him this long to get his PhD in electrical engineering. :-)
--

-MIKE-

"Playing is not something I do at night, it's my function in life"
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• posted on April 14, 2014, 12:55 pm
On 4/13/2014 11:34 PM, -MIKE- wrote:

LOL!
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• posted on April 15, 2014, 12:19 am
On Mon, 14 Apr 2014 17:43:21 -0500, Martin Eastburn
Sorta (as long as we're being pedantic ;-)

Sorta, kinda, perhaps poorly worded. Power is measured in watts. W=VA if the load is resistive.

Assuming there are no harmonics, which is a good approximation for an induction motor but may not be a good assumption for other situations. Electronic loads are often particularly bad. Fluorescent lighting is another example where the power factor (W/VA) is often particularly bad.

The important thing is that wiring and circuit elements (switches, breakers, connections, generation) must be sized for volt-amperes, where the power consumed (heat load, electric bill, etc.) is quantified by watts. VA is always equal (only for purely resistive loads) to or greater (all other cases) than watts. Reactive (either inductive or capacitive) loads cause additional problems not quantified by either.
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• posted on April 16, 2014, 4:01 am
You got it wrong. it is this : Power (measured in the watt) - Voltage (measured in the Volt) Times Current(measured in Amps) Times Cos(phase angle) (1 to 0 in value).
P = V*I*Cos(theta). When in DC Cos(0)=1. V is DC voltage in that case.
When in DC - it becomes : P = E*I where E is the DC voltage. I is the DC current and there isn't a phase angle or Theta is Zero and COS(0) = 1.
A Watt is the unit of power. Not the plural form.
When V is used it is AC. When V is used I is AC. They are in R.M.S. scaling. Root of the Mean Square. (A.C. volt meters and current transforms 'translate to these'.) Some times special voltages are used as design needs.
Harmonics from inductive and capacitive circuits are very small compared to the main current / voltage waveform. They are ignored if anything normal.
One should always use the phase angle in the AC model. Meters do. So the task for the technician is just measure it using a quality meter.
Even a reasonable multi-meter from Radio-Shack can measure Correctly (enough). I like three or four major makers and for the lab I use two.
V means AC voltage. E means DC voltage. I is the current that matches. Cosine(phase-angle) is Always used in AC.
One should design for several times that of V*A*Cos(0).
Martin - Senior Scientist and former Technologist serving between and working for both Intel and the Schlumberger. I'm working on my computer I built in the late 50's and early 60's. It has just under a thousand gates. All hand wired.
On 4/14/2014 7:19 PM, snipped-for-privacy@attt.bizz wrote:

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• posted on April 17, 2014, 12:06 am
On Tue, 15 Apr 2014 23:01:32 -0500, Martin Eastburn

No, I certainly don't. That formula only for SINE WAVES (i.e. no harmonics on either current or voltage waveforms). OTOH, PF=W/VA *always* works.

So? Again, sine waves are the trivial case. That formula doesn't work for nonlinear situations. The DC case is more than trivial. PF is meaningless.

Trivial cases are irrelevant. Not sure why you insist on lecturing on the trivial.

Plural is plural. Two times a watt is two watts. ...and if you really want to get pedantic about the language, "watt" is not capitalized. Proper names, when used as names of units are *not* capitalized. Abbreviations for proper names are.
Correct Incorrect W, V, A w, v, a watt Watt volt Volt ampere Ampere meter Meter m M

Whatever that means.

May be. That's the point, though. Your assumptions only work for sine waves and the conversion between Peak, RMS, whatever, is trivial, in that case. RMS is the voltage (or current) of a waveform that will give the equivalent power of a DC value. It's one of many meaningful numbers. The root of the mean square (for voltage or current) can be calculated, as can the average of the voltage X current (power).
No periods in RMS.

Again, "translate to" means "only valid for sine waves". If you aren't dealing with sine waves, these "translations" are meaningless. Worse, actually. They're wrong. A "true RMS" meter is always right (within it's physical capabilities).

Was that supposed to mean something?

Oh, good grief! Stop with the word salad, already. Harmonics from inductors and capacitors are ZERO. They're linear devices. Switching elements (semiconductors) are a whole different kettle, as is the real world.

Wrong. Meters certainly do not. They integrate V, A, V*A, or measure heat.

No, one should always use reality. It may be impossible to measure phase angle. It's always possible to measure V, I, and P. PF can then be derived from that, if necessary.

If they're "true RMS" meters, they're integrating type. If they're peak or average (rectified) meters, then they're calibrated assuming a sine wave. If you have something else (harmonics) then they're wrong.

Now you making stuff up. Wrong.

Whatever that means.

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• posted on April 18, 2014, 9:14 pm

Really simple to get around the 30 amp problem. Install a fused outlet. In the UK they are common devices, but not here, so you would install a fused (or breaker protected) disconnect on the 30 amp circuit, and connect the 115 volt outlets to that "sub panel"
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• posted on April 19, 2014, 7:16 pm
On Thursday, December 23, 2004 10:59:07 AM UTC-8, Keith Carlson wrote:

It used to be common, and my stove and clothesdryer both have 120V as well as 240V loads, and a three wire plug. This is now not recommended, and there's good reasons for a four-wire connection instead. In stoves, a convenience outlet is sometimes supplied, and this would have a separate fuse (or circuit breaker) so that the 30A fused stove doesn't cause a fire hazard on the 15A wiring plugged into that convenience outlet.
The clean solution (ask an electrician to be safe) is to run a four-wire line from your main breaker to a subpanel; then put any combination of 240V and 120V breakers into the subpanel, and wire your sockets from that subpanel. There's lots of rules on subpanel size and wiring, but it's what an inspector would want to see.
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• posted on April 19, 2014, 11:26 pm
wrote:

I think most were asuming 3 wire+ground (nmd3) cable. I know I was. The 3 terminal drier plug is history.