[rescue] Power Strip

Ron Wickersham rjw at alembic.com
Fri Oct 20 13:22:08 CDT 2006

On Fri, 20 Oct 2006, Ethan O'Toole wrote:

> > Hi people.  I'm looking for a 1U rackmount power strip that does 220v
> > (split) in and 110v out.  Anyone know who makes one?  Thanks.
> > Peace...  Sridhar
> I think your neutral will need to be twice as big all the way back to the
> box. Can anyone verify?

no the neutral current decreases when there are loads on both legs of
a split 220 feed to the limit of zero current in the neutral when there
are equal resistive loads on both legs.

so neutral conductor size equal on one leg is always sufficient and current
is equal to (in the case of loads on one side only) or less (in the case
of loads on both sides) than the current in the leg that is drawing the
maximum load.

for 220/110 feeds, the neutral is the center tap of a single-phase
transformer.   so the opposing hot leg is of the opposite polarity
(sometimes called 180 degrees out of phase).

in commercial and some industrial areas, there is poly-phase distribution
but in this case it's called 208/120 and the two phases are at 120 degrees.
there is no issue with splitting the feed to two 120 volt loads, but in
this case the neutral current won't be zero with equal resistive loads, but
even in this case the current will be less than if only one leg is loaded.

the power distribution units in older sun racks are often split like you
want but all are 2 or 3 rack units tall, so far as a rescue.


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