Galvanic isolation

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Galvanic isolation is the principle of isolating functional sections of electric systems so that charge-carrying particles cannot move from one section to another, i.e. there is no electrical current flowing directly from one section to the next. Energy and/or information can still be exchanged between the sections by other means, however, such as by capacitance, induction, electromagnetic waves, optical, acoustic, or mechanical means.

[edit] Overview

• Transformers couple by magnetic flux. Primary and secondary side have no electrical connection. The isolation voltage (industry standard) is measured in kilovolt.
• Optocouplers transmit information by light waves. The sender (light source) and receiver (photosensitive device) are electrically isolated.
• Autotransformers do not provide galvanic isolation.
• If two electric systems have a common ground, they are not galvanically isolated (by definition). The common ground might not have connection to functional poles, but might become connected at an undefined point of time. For this reason Isolation transformers do not supply a GND/earth pole (Ground (electricity)).

[edit] Appliances

• Optocouplers to decouple a secondary function block from a primary function block, connected to the power grid (or high voltage).
• Optocouplers to decouple one signal potential from another signal potential.
• Power sockets intended for electric razor supply must employ a residual-current device or an isolation transformer (to prevent an electric shock if the razor should be dropped into water).