a few weekends ago i had to rewire a 220v welder from a 3 prong dryer plug, to a 4 prong. at lowe's i kept asking if the 4 prong plug is 3 phase wiring, the answer every time was 'whats 3 phase wiring?". i found a diagram for rewiring a dryer for a 4 prong and it worked fine for the welder, so i didnt worry about it. but now im curious to know if the 4 prong plug was connected to 3 phase wiring. is 3 phase a common thing in residential areas? if not, i dont see the purpose for an extra contact in the plug.

(p.s. anyone have an oscilloscope they dont need? ill pay shipping!!) haha!

 

No, residential wiring is never three phase. You should have had four wire colors - black & red, the hot wires - while for the neutral, and green or bare for ground.

Ain't no such thing as an unneeded o'scope.

 

You are correct, but in some location you will find Black, Blue for the Hot conductors instead of Black and red.

 

so im assuming the black and red wires are basically the same wire.... ie same phase, voltage etc?

 

No, they are 180 out of phase. The alternator that makes the AC has two coils, joined at one point to make the common line. The voltage out of either coil is 120 VAC individually, but 240 VAC across both.

 

ahhh. ic, thank you!

 

well generally residential supplies are single phase with few homes as exception
at least in my country , the three pins are for earthing 9the larger and bit longer one, one for a neutral and other for live wire.
for a better answer try reading star and delta connections in transmission
as far as i know we get power supply from star connection in our house
which has one neutral and three diff phases 120 degrees out of phase.
out of which one phase reaches ur house with a neutral. this system has its own advantages. i am not sure of the colour coding right now , what if someone has colour blindness???.

i will send u a useless osc if u send me a useful one

 

For a run-down on the American "split phase" single phase system, see:
http://www.allaboutcircuits.com/vol_2/chpt_10/1.html