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Re: 220v/50hz power rig
From: "Steven M. Bellovin" <smb () research att com>
Date: Thu, 06 Sep 2001 08:01:25 -0400


In message <9n7a89$mkc$1 () ncc1701 cistron net>, Miquel van Smoorenburg writes:


Find a no-break UPS that can handle both 115/230 in and outputs 230


Note that Randy's requirements were for 10A at 220V, or 20A at 110V.  
Also note that 110V suffers greater voltage drops, so you want a really 
short line from the panel box, independent of any inefficiencies in the 
UPS.  (Power -- watts -- is I^2*R, so if you double the current the 
loss in a given piece of wire is 4x greater.  This is why power lines 
run at massively high voltages.)

Since the discussion is ongoing, I'll post the comments I sent Randy 
privately, wearing my hat as the co-author of the Wiring FAQ:

--------

You probably can't do precisely what you want.  10A at 220V is 20A at
110V, which you can find; however, unless the outlet is very close to 
the panel box, you may get enough voltage drop (at 110V it's more than 
at 220V) to matter.  And those specs look like the device is really 
intended for a 15A or 20A 220V circuit -- possible, but not common, in 
American houses.

OTOH -- as was pointed out by several folks on NANOG, every American 
house (and some American businesses) have 220V in the panel box, and 
many have 220V outlets in a few places.  The gadget is designed for 50/60 
hz, which means that that shouldn't matter.  The real issue in the U.S. 
is the power switch and assumptions about one line being neutral; for 
safety's sake, you should use a 220-to-220 isolation transformer, I 
believe.

Many businesses have 3-phase power instead, which provides 208V across 
two legs, rather than 220-240V.  I know that I don't know enough about 
3-phase to offer any advice.


                --Steve Bellovin, http://www.research.att.com/~smb



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