On Thu, 01 Aug 2019 12:48:32 -0400 Doug McGarrett <[email protected]> wrote:
> On 07/31/2019 09:08 PM, [email protected] wrote: > > An update | correction | recollection ;-) > > > > On Tuesday, July 30, 2019 11:34:43 AM [email protected] wrote: > >> I have seen diagrams in NEC code books for a different arrangement > >> to get 120 volt 3 phase power, but I don't recall ever actually > >> encountering that in real life. > > > > Oh, wow, how quickly I forget -- I did encounter systems like that, > > often for lighting in industrial applications, And, further, iirc, > > we could (and did) buy and install florescent light (and maybe > > HID?) fixtures designed to work on 208 volts, which we connected > > phase to phase in that kind of system. > > > > Of course, I could be misremembering. > > > >> In that case, iirc, 120 volt loads are connected from a hot > >> tap to the neutral wire (the 4th wire of the 3 phase arrangement), > >> and you get (nominally) 208 volts (RMS) connecting phase to > >> phase. I have seen things like motors that were rated like 240 / > >> 208 volts (or something like that). > > > > > Three-phase power comes in two varieties: delta and wye (Y). In > delta, there are only three wires, and you get power across any two > of the three phases. In the wye configuration, you get power from one > phase of the three to the center of the wye. > If I remember right, and I'm not sure I do, you get 208 VAC across two > points of the delta, and I THINK you get 120 VAC from an end point to > the center of the wye. > Yes, because over here it's 240V and 415.7V. Between phases is the phase-to-neutral voltage multiplied by the square root of 3. -- Joe
