Why choose 120 volts?

Seth Mattinen sethm at rollernet.us
Tue May 26 20:24:20 CDT 2009


Joe Greco wrote:
>> Once upon a time, Joe Greco <jgreco at ns.sol.net> said:
>>> And I don't like not having anywhere to plug in my power screwdriver's
>>> recharger...  I suppose I should see if I can find someplace that has
>>> a transformer of an appropriate size, or does anyone already have the
>>> part number for something that can provide a few hunderd milliamps of
>>> 120V from 208?  :-)
>> Isn't 208V usually provided as a connection across two phases of a 3
>> phase circuit?  In that case, you get 120V by going between one phase
>> and neutral (no transformer required).
> 
> Yes, but this doesn't imply that you have access to those other phases.
> It is easy enough to be delivered 208V single phase service in a data
> center environment.
> 
> ... JG

Correct. I have a Smart-UPS RT connected across two legs of 3 phase for
208. The unit does not have a neutral, only ground, so it's 3 wires in
and 3 out. The output is only 208 L-L with odd voltages on L-G. Since
there's no neutral, it can only be used to drive 208 loads or a
transformer for 120.

~Seth




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