[Boatanchors] Basic electricity question

[WA5CAB at cs.com]

Not necessarily so.  It depends on how the transformer or generator is 
configured (Delta or Wye/Star) and on the load.  Many three-phase loads like welding 
machines, HV power supplies for KW and above transmitters (required BA 
content), etc. will have single phase auxiliaries like relays, blowers, etc.  Often 
enough these are low voltage rather than high voltage (i.e., if the three 
phase distribution is wired 120/208 Wye they may be cheaper 120 volt units) and 
will require the neutral.  

Delta distribution systems in plants are not common except in special 
circumstances (we once had a pipe coating plant where the compressor pad was wired 
Delta to run six 150 HP compressors).  The more common Wye configured systems 
are five-wire systems (three hot, neutral and ground), even if the majority of 
three-phase loads (motors) don't need the neutral.  Plus it is common in 
industrial buildings that need both single and three-phase power to run 120/208 Wye, 
taking all the single phase 120 loads from line to neutral, single phase 240 
volt loads (with taps appropriately set) line to line, and three phase loads 
from line to line to line.  Same with 288/440 distribution.  3-phase 440 loads 
run line to line to line and building lighting (288 volt) runs line to 
neutral, with the total lighting load in the building being evenly distributed over 
the three phases.

In a message dated 1/13/2005 8:44:11 PM Central Standard Time, 
garyschafer at comcast.net writes: 
> 3 phase power as described by others can be thought of as 3 separate hot 
> lines. No neutral required. 

Robert & Susan Downs - Houston
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