rhkra...@gmail.com writes:
> An update | correction | recollection ;-)
>
> On Tuesday, July 30, 2019 11:34:43 AM rhkra...@gmail.com 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).
>
That's the way I understand it too. One of the buildings
we worked in at Oklahoma State University had low-voltage wiring
to the light switches. Pressing the On button turned on the
overhead light, accompanied by the click of a latching relay.
Pressing Off released the relay with another audible click from
above.
I asked one of the electricians as to why the fancy light
switches.
The building had 3-phase wiring for the air handlers and
the lights were powered phase-to-phase at 208 volts. This would
have been dangerous if someone took the plate off of a switch for
any reason because every wire would be hot between it and
anything else.
Martin
