On Monday 03 May 2004 22:14, Tony Duell wrote: Tony is right here. At least in Indiana, Illinois, and the Code Book, 208 three-phase is a "Y" setup with 120V from each phase to neutral, and 208V from phase to phase. 240V three-phase is a delta setup, with the neutral half-tapped between two phases, giving 240V phase-to-phase, 120V phase-to-neutral on two of the phases, and 208V phase-to-neutral on the third one. It's important to realize when wiring a system like this that the third phase is NOT 120V to neutral like the other two, I've heard of some people (idiots) ignoring that, and having issues when they tried to turn on their 120V lamps they just wired. : ) Agreed. Pat -- Purdue University ITAP/RCS --- http://www.itap.purdue.edu/rcs/ The Computer Refuge --- http://computer-refuge.org

On Monday 03 May 2004 23:14, Don Maslin wrote: When a neutral is put on a delta, it's wired like: A / \ / \ B--N--C At least, that's what I've learned from reading NEC code books. By contrast, a wye aka Y/star is wired like: A B \ / \ / N | | C I guess you could also call that a "flux capacitor" arrangement. :) You can also put the ground one of the three delta phases, and end up with this: A / \ / \ B/N----C I've only heard of that arrangement before, I haven't actually seen it. In general, though, it seems intuitive to me that you'd want to connect some part of the secondary to ground, and avoid a floating secondary, as you might run into "problems" if your 12kV(ish) primary becomes coupled to the secondary, and there isn't a ground path to trip a circuit breaker. There's few things more dangerous than having your 208V line at 12kV+-208V (AC RMS) to ground when you're not expecting it. -- Purdue University ITAP/RCS --- http://www.itap.purdue.edu/rcs/ The Computer Refuge --- http://computer-refuge.org

On Tuesday 04 May 2004 00:19, der Mouse wrote: No, it is a neutral, because it is grounded. On a three-phase delta, you ground the center tap of one (only one!) of the phases. In all of my examples, the neutrals were "grounded neutrals". Maybe I should have been more clear about that. Pat -- Purdue University ITAP/RCS --- http://www.itap.purdue.edu/rcs/ The Computer Refuge --- http://computer-refuge.org

Clash of assumptions - I had been assuming that the three phases of three-phase were symmetric with respect to ground. I see that's not always so.... /~\ The ASCII der Mouse \ / Ribbon Campaign X Against HTML mouse(a)rodents.montreal.qc.ca / \ Email! 7D C8 61 52 5D E7 2D 39 4E F1 31 3E E8 B3 27 4B

On Tuesday 04 May 2004 17:54, Tony Duell wrote: Sure, there is. It's the voltage potential present on a long electrode inserted into the earth. :) Exactly. Pat -- Purdue University ITAP/RCS --- http://www.itap.purdue.edu/rcs/ The Computer Refuge --- http://computer-refuge.org

And just what do I connect the other lead of my voltmeter to? :-) Incidentally, 'There is no such thing as groud' is one of Voanda's laws and has 2 meanings. The first is the one I am using there, that voltmeters have 2 leads, and it's arbitrary where you connect the 'refernce' lead to. The second is that any real connection has impedance, and that the 'ground' in a high-speed digital circuit may not be quite the same voltage everywhere. In fact 'ground bounce' -- mostly due to the inductance of the ground connection -- is a problem in laying out high speed circuitry. -tony

On Tue, 2004-05-04 at 21:50, Patrick Finnegan wrote: Apocryphal tales to terrorize know-nothings: To someone you see coil up a long extention cord and plug the ends together for convenient storage: "STOP! Don't do that! The electricity will build up in the loop and later shock you when you unplug it!", proceed to show them how to discharge (sic) the cord by wailing the coiled cord on the ground a dozen times. Point out (non-existent) stains on the floor under electrical outlets, and the real reason behind those "baby-proofing" snap-in plastic plugs that push into unused outlets -- they keep the electricity from leaking out and staining the floor. Point out that ordinary electrical tape over the unused holes will do in a pinch. Then there's always the "AC battery" which you send neophytes out to look for, but that tale is older than my now-deceased grandfather, though I suppose it happened at least once. (Wait, we had all those power cube arguments...)

<pedant> Actually, there is: any sufficiently large object containing equal amounts of positive and negative charge will do. (The size matters because in most respects the object in question must be at least potentially able to accept a substantial amount of electric charge.) For the voltages and currents involved in this discussion, the only available object that even approximates that is the earth, but that doesn't invalidate the basic point. When working with very high voltages and low currents (which in my experience has been almost entirely gedanken), I have to keep reminding myself of that: there is potential current flow whenever there is a difference in overall charge, regardless of how that difference got there. For most electronic and electrical purposes, the capacitances involved are small enough compared to the voltages and currents involved that we can pretend that an isolated circuit is unreferenced to ground, but that's merely a handy approximation, not a Truth. Of course, this doesn't invalidate the point that given decent transformer insulation, you can ground any single point you please of a three-phase (whether delta or wye, actually - but grounding other than the central point of a wye would be Weird). My initial objection was based on unstated (and incorrect) assumptions.... /~\ The ASCII der Mouse \ / Ribbon Campaign X Against HTML mouse(a)rodents.montreal.qc.ca / \ Email! 7D C8 61 52 5D E7 2D 39 4E F1 31 3E E8 B3 27 4B

On Tue, 4 May 2004 04:14:44 +0100 (BST) ard(a)p850ug1.demon.co.uk (Tony Duell) wrote: The VAX6000 has a controled (?) six pulse rectifier that generates 400V DC from three phase mains. This DC current is distributed to the individual PSUs. -- tsch??, Jochen Homepage: http://www.unixag-kl.fh-kl.de/~jkunz/