Re: [CAD_CAM_EDM_DRO] Re[1]: FYI: Home Depot Good buy on conns/cables 20' 3...

In a message dated 10/3/00 2:25:07 PM Pacific Daylight Time,
Ian@... writes:

<< is the realisation from what has been said that you may have two phase
power
to your homes and, even more surprising that both phases may be available at
a wall outlet! Can this be true?? >>

The electrical distribution system I am used to in the US is to generate
three phase current at the power house. Raise the voltage to 4800 volts for
in city distribution fed to primary windings of transformers either on power
poles or underground down to 240 volts. In industrial areas the three phase
is carried to factorys and shops, but residential uses take a single phase
off the transformers at 240 volts. (In some areas I worked you would see two
large transformers and one small one in a vault) The 240 is fed to the house
via a three wire system with 120 volts each side of a neutral. The house is
wired to attempt to share the load on each side of the 240 with some services
on each leg at 120 volts for lamps, radios, TVs (and PCs). If electric
cooking ranges and/or clothes dryers are installed they run on 240 volt
outlets. Each outlet either 120 or 240 is made so plugs will enter only one
way to assure the neutral line is continous (unless some user has clipped off
the ground pin, and filed or cut the "wide" leg of the plug.) The whole
system is grounded to a metal water service pipe or an earth ground. The
ground wire is a third uninsulated wire in the cables used to wire to the
outlets. The convention (I don't have a current copy of the NEC "National
Electrical Code" here to check) is to have a green attachement at each outlet
for ground, some color (black or red) for "hot" and white for neutral.
Maybe someone more familier with house wiring can give you a better answer.
This system came into use during my adult years and you can find old houses
without the grounding "hole" in the receptiple and no provision for the
"wide" leg so things can be plugged in either way, leaving the lamp socket
shell "hot" except for a little cardboard sleeve. SCARY!
John Meacham
(A mechanical engineer, but hung around some electrical EEs)