An isolation transformer is a transformer used to transfer electrical power from a source of alternating current (AC) power to some equipment or device while isolating the powered device from the power source. For safety, isolation transformers provide galvanic isolation and are used to protect against electric shock, to suppress electrical noise in sensitive devices, or to transfer power between two circuits which must not be connected (ie test equipment like a oscilloscope). Isolation transformers block transmission of the DC component in signals from one circuit to the other, but allow AC components in signals to pass.
Isolation transformers block interference caused by ground loops. Isolation transformers with electrostatic shields are used for power supplies for sensitive equipment such as computer or laboratory instruments. I have four isolation transformers in my radio room. Without the isolation exposed live metal in a device (such as a radio chassis) under test is at a hazardous voltage relative to grounded objects such as a oscilloscope ground lead. A particular hazard with some old vacuum tube radios is with a live chassis. Any true transformer is isolating, as the primary and secondary are not connected by conductors but only by induction. A transformer sold for isolation is often built with special insulation between the input and output. A simple 1:1 isolation transformer will have a 115 VAC primary (input) and 115 VAC Secondary (output). Look at the YouTube video from Todd Fun on isolation transformers: http://www.youtube.com/watch?v=11Yve2ijWyk.
