You breaker box bus bars are designed so that every other slot going
down each side are on alternate busses. Go to your local Home Depot or
whatever and look at one of the circuit breaker panel boxes on display.
Once you see one opened up and empty, it'll all make sense.
Typically a house is supplied with a single 240volt phase center tapped.
Neutral is connected to this center tap and thus pole to pole voltage is
240 and pole to centertap is 120.
208 volt service is derived from 120 volt three phase "wye" power where
one pole from each phase is tied together. Neutral is connected to this
junction which yields 120 volts pole to neutral and 208 volts pole to
pole. The difference is that the 208 is derived from two phases that are
120 degrees apart. 120 volts * sin(pi/3) * 2 = 207.6 volts.
Some utility companies just tap into two phases to give the 208 to a
residential unit, though this is rare. Usually they step a single 7200
volt or so single phase line into center tapped 240.
My bad, the stated voltage is the maximum pole to pole voltage
For those interested, the diagram at the bottom of the page details this.
I'm an electrician living in Canada. Pay attention to that.
120V5V0V. These are the same voltage. Single phase. Used in a
220V-240V are the same. Single phase also. Used only for bake oven and
208V is the voltage of a 3 phase circuit. I suggest you go outside and
check out the wire(s) that connect your house.
If the wire has 3 wires, 2 black cover wires and an uncovered aluminum
ground wired, it is the single phase one 120/240. Every house has this
If the wire has 4 wires, 3 black cover wires and an uncovered aluminum
ground wired, it is the 3 phase voltage 208V.
You can have both of them connected to your house. It is rare but it
can happen. Pay attention to that.
Also, you can't replace 208V by 220V. It's not the same thing at all.
I suggest you call someone who knows well electricity (an electrician)
before attempting to do something with it, if you don't want to burn
any electric things.
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