3 phase residential with one leg 'out' - Page 3

 
daestrom wrote:

Yes and all the voltages are very "nominal".

 
Thanks Pete – I think you are spot on. Apologies I erred in the
original post – I have 4 wires coming from pole – I didn’t realize
until closer examination that the support/anchor cable for the 3 hot
wires was also the ‘neutral’ 4th wire (and I so figured  the ground
connections I asked about in original post are fine)
Wish I could attach diagram at end of this website - see:
http://www.eng-tips.com/viewthread.cfm?qid=157326
It must be my exact 3-phase setup.  From that diagram - measuring
between (house inputs) ‘a’, ‘b’, and ‘c’ I measure 240, 238, an=
d 235
volts ( I can not easily measure ‘c’ (wild leg) to neutral to see if
209 volts exist there). BTW – the ‘ranch panel’ DOES have 110
circuits.
Something bothering me is that I get 240V between ‘a’ and ‘b’, but
only 108 and 105 volts from those points to neutral (measured at
breaker box bus bar and bar input cable roof anchor) – I was expecting
120 volts (not 105 volts).
Thank you Pete, and Norman, for the input – I learned much…

 
Pete C. wrote in message

I'll have to have a think about this but what about the phase of each leg?
 A centre tapped transformer will be in phase or 180 degrees out of phase.

A three phase induction motor works with the 3 phases 120 degrees out of
phase.

In the mean time I'll google "open Delta"

Regards
Norm

 
Norman Webb wrote:

The three hot legs are indeed 120 degrees out of phase since the
transformers are fed from three phase lines. The exact details on the
center tapped transformer vary depending on whether the high side is fed
Wye or Delta, but it doesn't matter much from your perspective since you
still get the expected voltages.

 


Nope.  He has 120/240 single phase service and 240 3 phase compliments of the
wild leg that also happens to be nominally 208 volts to neutral, NOT to be
confused with 208/120 delta service.  This is called "split open delta" and
not just open delta.  It could also be "split closed delta" which is what I
had since I had many more 3 phase loads than the average house.  The 3rd
transformer gave me better three phase voltage regulation.


Please use the modern notation of 120/240.  110/220 has been gone for half a
century.  quoting it the old way screws up newbies trying to make the math
work.


That is true per the math ( (120+240)/sqrt(3)) ) but the voltages usually
aren't exactly 120 and 240.  Mine was a bit high so that my wild leg ran 214
to ground on average.

That was handy for a number of things including operating some British-market
appliances that I had a Brit friend send me.  Their system expects 230 on one
leg and neutral on the other.  I liked running the wild leg to outlets for
those devices better than I did conventional 240 with each leg 120 to ground.
Just in case the Brit manufacturer took the same shortcuts as US mfrs used to
and tied the neutral to the case.

Since a 240 volt appliance can draw twice the power as a 120 volt appliance
from the same ampacity circuit, Brit stuff is much nicer to use.  A tea pot
boils water MUCH faster then even a gas stove heated American one.

John
--
John De Armond
See my website for my current email address
http://www.neon-john.com
http://www.johndearmond.com  <-- best little blog on the net!
Tellico Plains, Occupied TN
The profligate use of energy is the sign of a healthy, expanding civilization.
Conservation is a leap backward toward the caves.