Does anyone know what is meant by electrical isolation? From this schematic: url=http://upload.wikimedia.org/wikipedia/en/1/12/Swer.gif I don't see the significance of calling the transformer an "isolation transformer". What is the difference between a transformer and an isolation transformer? What is the isolation transformer doing in the circuit? Why is the step-down a measly 3 kV? Also, just to make sure I understand the definition of electrical isolation, is this correct: If you have two separate circuits A and B, and take one (and only one) wire and connect them together, then that has no effect on the voltages and currents in each individual circuit. It establishes a common ground, but does not effect the circuits' behavior. So do two circuits that have a common ground but are not connected to each other at any other point, isolated circuits? Or does electrical isolation mean floating, in which case A and B are not floating with respect to each other when you connect a wire between them?