Well, the thing works in any case so I’m willing to leave it at that. If you are a user all you need to do is hook up the ground fault interrupter in accordance with the directions in the box and stand back.
The OP’s not dismantling this thing and bringing wires out to wall outlets, is he?
You’re not, are you, bardos
No. Of course not.
Yes, he has wires running all over the house.
No, they are in phase.
If I hook Channel A of an oscilloscope to one conductor, and Channel B of the same oscilloscope to the other conductor, the CRT will show two currents that are in phase.
Think for a moment, Crafter_Man.
Just hooking “Channel A of an oscilloscope to one conductor, and Channel B of the same oscilloscope to the other conductor” isn’t going to show you currents at all, is it. It’ll show you voltages.
You need to do something else to determine currents. Like measure voltage drop across a resistance, or voltage induced in a current transformer.
And whenever you do something like that, you need to define a reference direction.
Whichever way you define the reference direction, you end up with “same phase but in the opposite direction”, or “opposite phase, same direction”.
Desmostylus:
I am very well aware that a shunt resistor or current sensing device would be needed to measure current. (I’m an EE for Christ’s sake.) Those are low-level details that have absolutely nothing to do with the point I was trying to make. The point I was trying to make is that the two currents should be perfectly in phase at all times. (Besides, if shunt resistors were used, differential & isolated measurement techniques would have to be used. And I really don’t want to get into that…)
When us EE’s talk about “phase” of voltage or current, it is always assumed that we are talking about phase relative to time. Current is not a vector quantity; it is charge per unit time. That’s it. Note that no spatial quantities show up in the definition.
Yes, current density does have a spatial direction, and I hope we’re all aware that electric and magnetic fields are vector quantities. But Q.E.D. and others said the currents were out of phase. And, well, being the purist I am…
Yoiks! :eek:
You know what most people think when they keep blowing fuses?
“Damn fuse must be too small.”
Believe me. I worked as a maintenance electrician, around lab people, for many years.
Lab tech “Hey, you got a fuse this size, only 15 amps?”
Me “This one’s only 10 amps.”
LT “Yeah, it’s too small.”
Me “How do you know that?”
LT “Cause it keeps blowing.”
Me “Let’s go have a look.”
Me, in his lab “You’re trying to run a 2000w heater with a 10a controller.”
LT “Yeah. The fuse is too small though.”
You got me worried, bardos.
Wait a minnit, we haven’t heard from the OP for awhile. Oh oh.
Baaardooos.
Dang.
You’d be aware, then, that there are these frequency domain quantities called phasors? And that phasors are represented by vectors? And that analysis of steady state power system behaviour is almost exclusively performed in the frequency domain, and using said phasors? And that there’s absolutely no difference between saying that a current has “the same phase but opposite direction” and saying that it has “opposite phase but the same direction”?
Substitute the term “sense” or “polarity” for “direction” if it makes you feel more comfortable.
Um, yes. Do I have to perform some Fourier Analysis or calculate some Laplace Transforms for you? I have neither the time nor energy.
I think the point has been lost in the noise. And the point is this: If my coworker yells across the room, “Hey Crafter_Man! I just measured two currents on this circuit board, and they’re in phase!” the physical direction of the current is not the first thing that will pop into my mind. (Unless, of course, we’re talking about a distributive parameter system.) What I will assume – what any EE will assume – is that they’re in phase in the time domain. Of course, saying that “they’re in phase but traveling in the opposite direction” is perfectly fine, but it would be incorrect (or at the very least, extremely confusing and unconventional) to say that the currents are “out of phase.”
The point isn’t being lost in the noise. I don’t think you have a point at all.
What would you say if you coworker yelled across the room, “Hey, Crafter_Man! I just measured two currents on this circuit board, and they’re 180[sup]o[/sup] out of phase!” Would you simply respond “No they aren’t”? Would you be completely unable to comprehend such a situation at all?
And BTW, it doesn’t help you to insist on a time domain representation - the time and frequency domain representations are simply alternate representations of the same thing. If you use time domain, you still get the same result.
If
I[sub]1[/sub] = e[sup]j[symbol]w[/symbol]t[/sup], and
I[sub]2[/sub] = e[sup]j([symbol]w[/symbol]t+[symbol]p[/symbol])[/sup],
then it’s quite obvious that
I[sub]1[/sub] and I[sub]2[/sub] differ in phase by [symbol]p[/symbol] radians, or equivalently they’re 180[sup]o[/sup] “out of phase”.
It’s also quite obvious using the trig identity
sin([symbol]q[/symbol]) = - sin([symbol]q[/symbol]+[symbol]p[/symbol])
that
I[sub]1[/sub] = - I[sub]2[/sub].
Should read:
It’s also quite obvious using the trig identities
sin([symbol]q[/symbol]) = - sin([symbol]q[/symbol]+[symbol]p[/symbol])**, and
cos([symbol]q[/symbol]) = - cos([symbol]q[/symbol]+[symbol]p[/symbol])**
Desmostylus: I don’t know how many ways to tell you this; Believe it or not, I understand frequency domain representation. I understand time domain representation. I understand that there are different ways of describing the same signal.
But you are completely missing the point. If Joe Blow says that two currents are 180 degrees out of phase, then it is assume one is time-shifted by pi radians. This is extremely basic stuff.
All I can say is, thank God I graduated from a U.S. engineering school… :rolleyes:
What the fuck are you talking about?
I just posted the time domain representation, remember:
What did you think the “t” stood for? Would it have made any difference if I’d said “[symbol]p[/symbol] radians out of phase”? Or “differ in phase by 180[sup]o[/sup]”? Yes, it is very basic stuff, and I don’t think you understand it as well as you might think you do.
I repeat: I don’t think you have a point.
Vulgar language aside, the original point was that it’s incorrect to say the two conductors are 180 degrees out of phase, as was originally stated by Q.E.D. Other than that, I give up. :rolleyes:
Let’s not forget how this started:
That was how you began your attack on billy, whose posts in this thread have not been inaccurate in any way at all.
Then, you made an assertion contradicting one of Q.E.D.'s posts. Q.E.D. isn’t an EE, and as far as I can tell, was perfectly willing to listen to David Simmons, who is.
Then you started arguing with me. I have no idea why. You don’t have any factual basis for doing so.
Here’s what Q.E.D. actually said:
How you could possibly read that as “the two conductors are 180 degrees out of phase” is beyond me.
You are making a complete and utter fool of yourself here, Crafter_Man.
A fool? Save it for the Pit.
Anyway, Q.E.D. said the currents were “opposite in phase.” This doesn’t sound like “in phase” to me. In fact, a conventional and reasonable person (or any EE here in the States) would interpret the word “opposite” to mean 180 degrees out of phase. When I told him they were in fact in phase, he said “I don’t think so.”
The only problem here is when Q.E.D. said, “"Under normal operation the current flow in both conductors is equal and opposite in phase and cancels each other.” This is not correct, and 99.99% of EE’s here in the States would agree with me. Other than that, I think we’re all in agreement (at least I hope).
To be fair to Crafter_Man, I did mean “180 degrees out of phase”. And I still think it’s semantic quibbling to say it’s wrong to view it like that, though I’ll admit it’s generally useful to have one standard frame of reference that everyone agrees to use. So, I’ll use it too from now on.
Q.E.D.: I’m not blaming you. You’re quite sharp when it comes to these things, and it’s obvious you understand the phenomenon that’s taking place, but the wording was simply in error. An innocent mistake, which I have done countless times. But in the spirit of the Straight Dope I corrected it anyway, and now I’m being raked over the coals for no apparent reason.
I know it, C_M. But FWIW, I’m with Desmostylus on this one, potshots aside. I found it more instructive to use the frequency domain in this case, since saying the currents are 180[sup]o[/sup] leads to a more intuitive understanding of why the magnetic fields cancel. Your explanation, based in the time domain, is perfectly correct but less intuitive, IMO.
There is a similar circumstance in physics, where you can have either an inertial frame of reference, or an acceleration one. Both are perfectly correct and interchangeable, but often it is more instructive to use one over the other.
Desmostylus, play nice, man. I took no offense whatseover to Crafter_Man’s posts.
Grrrr…make that: “…180[sup]o[/sup] **out of phase…”