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Subject - 220v, 208v and other wonderful issues.
lesfalconer Coming from a country that uses 220v (1 phase wire and 1 neutral wire), it is confusing how we arrive at 220 volt in the US. Can someone explain the way that 2 phases are used and where the neutral comes into play. For example, if a 220v single phase piece of equipment is to be powered, are there 3 wires to it with 2 phases and a neutral??

Also, what does 208v get used for??? That throws me for a loop!!

Thanks,
Les
Scott Vickrey Have a look at this diagram. For simplicity concider 220 volts the same as 240 volts and 110 volts the same as 120 volts. 240/120 are called nominal voltages and this is what we use in calculations in the United States.

This is a diagram of the secondary windings at the transformer. The 120 volts from the black to white and from red to white are called phase voltages. We can obtain 120 volts potential from these wires(after a disconnecting means and overcurrent protection device). The 240 volts from the red to black is known as the line voltage. We can obtain 240 volts potential from these wires(after a disconnecting means and overcurrent protection device). The green wire will serve as a safety sytem by keeping all the metal parts of the sytem at zero volts.
If a 220v single phase piece of equipment is to be powered, are there 3 wires to it with 2 phases and a neutral??
No neutral is required for the circuit you described.
208 is a line voltage you get from a three phase 208/120 volt wye connected secondary. Sorry I have no diagram for that. Maybe I'll make one tommorrow.
lesfalconer OK, I now understand the line voltage. One more question. Is the green (ground??) simply connected to the cabinet or metal part of the transformer and then grounded? Or is it a part of the secondary winding??
Thanks Scott,
Les
ps The 208/120 diagram would be interesting when you get a chance. Thanks for your help.
Scott Vickrey The ground wire connects to the neutral, transformer winding center, grounding electrode and the all the metal equipment.
Mitch Nice diagram Scott.
trek2001 So, do the neutral currents cancel out like three phase ?