Phases of understanding

I am not an electrical engineer, nor am I an electrician. By all rights, I am far from qualified to comment on polyphase power, but I have to throw in a few words. Based on my limited understanding of three-phase power, I can surmise that you are provided with three hot leads, each of which carries alternating current electrical power at the same frequency, but with shifts, or phases. Typically, for three phase power (or, perhaps always) this means a shift of 120 degrees between each of the three phases. Now, if you have two 110 hot leads which are 180 degrees apart in waveform, then you have a traditional US residential power potential of 110 to 220 volts (depending on the power of the two hots). However, with three phase power, you actually have 120 degrees of separation between the waveforms, not 180, meaning that you have sqrt(3)*(potential of hot), not double, if you're using two hot poles. (image is from Wikipedia)

So, what got me started on this? At one point last week, I had the opportunity to ask if we had 'three phase power feed, and thus 208v of potential' for the power feeds to the bladeframes. The response that I got was to the effect of 'we don't have three phase power, it's 208v.' Since the Liebert unit (and it's monster compressors) run on three phase power invariably, and since that is really the only normal explanation for having 208v of potential, I had to run out and ensure that my limited EE knowledge had not failed me. I can now rest assured that it hasn't.

-AJB.

P.S. More pictures
I've also, as you might have guessed, taken far more pictures then I've posted to this blog (maybe you wouldn't have guessed that). Our upload bandwidth here at trinity is rather limited, and I don't have time (even batch processing time) to reduce the resolution of the images that I've taken, so, what I'm saying, is that they take forever to upload. But, since I have a few minutes now, I'll throw up a few more.

This first image is utterly insignificant except that it's a Halon 1211 fire extinguisher. These relics should not be used without a breathing apparatus, but it sure beats a bunch of wet computer hardware. The next image goes well with the theme of water on electrical equipment: it's our EPO button. Something about seeing them just forces me to remind myself "look with your eyes andrew, not your hands." I have similar thoughts when getting on ski lifts. It's so unfair that those damn lift operators get to hit those huge buttons and we don't! I might have watched a bit too much MacGyver when I was little. The third image is of a note attached to the upper compressor in our Liebert unit. I don't understand really anything about the way these things work, but I am unsettled by a note saying that something was almost stripped off in 1995. This thing needs to work for at least as long as our new cluster is useful.


The first picture here on the left is a reminder that 61A was a telecom closet (in many ways, it may very well still be). This wall clearly had a lot of stuff mounted on it at some point. The blue wire coming down from the ceiling is a 50? conductor cable that is going to be terminated in the 2 post open telco rack to provide our drop. That black wire coming out of the wall is actually a 12 fiber bundle, which at the very least is disused, but at least two of the fibers appear to be totaled (their ends are cut off). The picture on the right is of a bunch of APC units that we removed from the back of the bladeframes. My understanding is that these things are used for redundant power legs, or possibly redundant UPS units (is there a serious effective difference?) We don't have that many circuits, or that much money (how much would a UPS like that cost anyway?) so these are pending removal off to some other location, like the computing center, or ebay. Oh! I almost forgot. You can just barely see the top of a digital vt320 dumb terminal in the left image. Dunno what's going to happen to that yet.

P.P.S. My post seems to have changed to arial without asking me. I must be hitting tab too much.