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

Well, I'm not an EE, but where I went to engineering school, sqrt(-1) = i. I also can't find a reference for it via Google. Do you have a reference for it? I'm not saying you're wrong, just that I've never heard of it, and I've been exposed to enough EE back in my school daze to know what reactance is and power factor and some of that cool polyphase stuff.

todd

Hello all, First i want to say Merry Christmas all. For the curious the point of three phase was to provide a better power feed for motors. the concept of the rotating magnetic field works better when instead of a single coil; you have three . It gives you much more power available at any one spot on the armature. The three phases are 120 degrees out of phase with each other. A.C. starts at 0volts and goes to +120v then return to 0v then goes to -120 then completing the cycle returns to 0v. When you have 3 phases they(the power company) stagger them so the first phase starts to rise then the second then the third and they follow each other thru the cycle so they reach 120v slightly after each other. Instead of only getting 120v 60 times a second we now get three separate phases providing 120vac. So 3* 60 times a second = 180 times a second we now get power, 3 phase motors run much smoother because of this.

Todd Fatheree wrote: ...

j for sqrt(-1) is quite common in EE, probably more so than i which is more prevalent in mathematics or physics. One reason is that "i" is so often used for current in EE.

As for reference, let's see...

Ok, here

T(jw) = G(jw)/(1 + G(jw)) --> ~1, |G(jw)| >> 1 Eq (8-60)

Closed-loop transfer function frequency response.

Feedback Control Systems, Phillips & Harbor, Prentice-Hall. ISBN

We called that "j". Always lower-case, and never with a "-factor" on the end.

It is interesting that you mention that. It certainly is possible to build a 4-phase generator. I've never seen or heard of one, but it would be no big deal to build one. You would really have 4 windings, not four brushes, but that's a detail.

Now, let's try an experiment. Label the 4 phases A, B, C, and D, in order. Assume the windings are star-connected, so there's a common neutral, which we'll label N. Let's further assume that the leg-neutral voltage of each phase is 120 VAC.

I'm going to give you two panels, each having three terminals on it. One both panels, the terminals are labeled X, Y, and N. One one panel, X and Y are connected to phases A and C from our 4-phase generator, and N is connected to the neutral. On the other, X and Y are connected to L1 and L2 from a typical center-tapped 240V residential pole drop, and N is connected to the center tap. On both panels, N is tied to earth at the panel.

Can you describe a measurement that you can make, which will tell you which panel is connected to the 4-phase generator and which is connected to the pole drop? You can use voltmeters, ammeters, power meters, phase meters, oscilloscopes, or any other tool or instrument you desire. Assume, however, that both are ideal voltage sources, i.e. you can't draw enough current from them to significantly load them down.

My claim is that you can't tell the difference.

If you had been an EE, you would have learned that sqrt(-1) = j. In electrical engineering, the symbol i was already taken (it means current). So, electrical engineers just break with tradition and use j for sqrt(-1) instead of i. It looks a little weird at first, but you get used to it.

When I was in school, the EE courses used j and the math and physics courses used i. You just learn to shift mental gears depending on which class you're in.

The only other place I've seen j used for sqrt(-1) is in the Python programming language

...and the reason it's "i" in mathematics is that it stands for the "imaginary" number = sqrt(-1).

- Doug

...

Very sound advice. Newsgroups, while full of very good advice are also full of wive's tales and anecdotal experiences which get stretched to become trueisms.

The insurance company part of this statement is one of those truisms. Insurance companies pay off every single day on house fires that the Cause and Origin Team has determined started with faulty wiring. Bad wiring, not simply wiring that mice worked on, etc. In most, if not all states, insurance companies have to pay against acts of stupidity. Check with an adjuster.

leg-neutral

connected

Ok this is a bit dirty but you didn't mention bonding the 4 phase generator to ground anywhere but at the panel. So I would take both panels and remove the ground wire from the ground bus in the panel ( watch for all the heavy arcing! ) then i would take my voltage meter and read voltages from any leg to the ground wire coming from the ground. Since you did not bond your generator anywhere but at the panel if you ever lose ground ( screw loosens ,cooper loss, thermal stretching) at that panel voltage will float and be different ;) M.E.Farmer

ROTFLMAO!! It's a "standoff" only because you won't [cant'?] answer the question.

Regards, Doug Miller (alphageek-at-milmac-dot-com)

Get a copy of my NEW AND IMPROVED TrollFilter for NewsProxy/Nfilter by sending email to autoresponder at filterinfo-at-milmac-dot-com You must use your REAL email address to get a response.

Actually, you haven't the first clue what you're talking about. I hope that your time in the tech school wasn't spent teaching how residential electrical service works.

You wrote that adding a 120V load to a 240V three-wire ["Edison"] circuit doubles the current in the neutral wire, and creates a dangerous overload.

It does nothing of the kind.

And I'd love to see your explanation of how it could.

Apparently, neither do you.

-- Regards, Doug Miller (alphageek-at-milmac-dot-com)

Get a copy of my NEW AND IMPROVED TrollFilter for NewsProxy/Nfilter by sending email to autoresponder at filterinfo-at-milmac-dot-com You must use your REAL email address to get a response.

On Sat, 25 Dec 2004 07:34:46 -0700, Duane Bozarth wrote (in article ):

Hey, I have that book!

-Bruce (EE control systems engineer)

Bruce wrote: ...

It's one of many I've picked up over the years -- not too bad although I've not used it too much...I was NE at the time I was doing most control stuff so most of my early exposure was to reactor controls...I picked up the EE controls stuff much, much later... :)

I have to confess that I never understood what the square root of -1 was. The product of what times itself will equal -1? I guess I have a brain molded around neutonian physics, now a little too old to understand....

Dave

"i" or "j" depending on whose notation you want... :)

"i" or "j" ... think of it simply as "by definition" that j*j = -1 and anywhere you need it you make the substitution and carry on...leads to the expansion of the "real" numbers to include the "complex" numbers of the form "a +/- jb", for 2 + 3j. Rules for things like addition/subtraction are add real and imaginary parts separatel, multiplication is like algebraic...

(2+3j)*(1+2j) = 2*1 + (2*2j+3j*1) + 2j*3j = 2 + 7j + 6j**2 = 2 + 7j + 6*(-1) = 2-6 + 7j = -4 + 7j

Clear as mud? :) Notice all that was done in last simplification was to associate terms and substitute -1 for the j-squared term.

If you're talking about 120 volt RMS,and I think you are, the voltage will peak at ~ +170 volts and -170 volts.

R, Tom Q. Remove bogusinfo to reply.

The breakers you have may have a **very** short time current curve (you can always get different breakers with longer curves) or the motor may pull excessive startup currrent (tho this isn't my area of expertise). Once the motor is up to speed, the current will stablize -- so you can judge by ear how long the surge will last.

Matthew

There is a common misconception about watts and volt-amperes. People misunderstands both

the same. But there is a whole different way of calculating the both. W and VA are both units of measurement for power, but that's where the similarity ends.

Watts do work or generate heat, while volt-amperes simply provide you with information you

need to size wires, fuses, or circuit breakers. Watts add linearly, while volt-amperes doe

not. And to measure W, you need a special wattmeter. You can calculate VA by using a

standard multimeter to measure VRMS and IRMS and finding the product The idea for determining the Real power VS apparent power for ac is uncomplicated, We care less of apparent power, its the utilitys problem! it is true true,or CONSIDERED

true for all practical purposes for circuits having motors,etc. Electronic products list ac line voltage,frequency, and Amp ratings.

1 watt Watts (W) is calculated by multiplying Volts (V) times Amps (A), so 1W = 1VA true true,or CONSIDERED true for all practical purposes In reality A pf OF .9 WILL MAKE 1 AMP ABOUT .93 AMPS.