Galvanic isolation

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 electric 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.

Galvanic isolation is used in situations where two or more electric circuits must communicate, but their grounds may be at different potentials. It is an effective method of breaking ground loops by preventing unwanted current from travelling between two units sharing a ground conductor. Galvanic isolation is also used for safety considerations, preventing accidental current from reaching the ground (the building floor) through a person's body.

Overview

• Transformers couple by magnetic flux. Primary and secondary side have no electrical connection. The isolation voltage (industry standard) is measured in kilovolt. The same applies to transductors.
• Optocouplers transmit information by light waves. The sender (light source) and receiver (photosensitive device) are electrically isolated.
• Capacitors transmit information and energy by an electric field. As it is possible for some capacitors to fail short circuit, there are special ratings for capacitors used for isolation, such as "Class Y" .
• Autotransformers do not provide galvanic isolation.
• If two electronic 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.

Applications

• 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.
• Transformers to allow the output of a device to "float" relative to ground to avoid potential ground loops.
• Transformers to increase the safety of a device, so that a person touching a live portion of the circuit will not have current flow through them to earth.
• 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).
• Yachts connected to improper grounded shore supply systems should employ a galvanic isolator to isolate from any stray currents in the marina (either from the shore mains or neighbouring yachts). Without the isolator, a galvanic corrosion path may be created damaging metal equipment below the waterline. Zinc anodes may help to prevent this, but often prove insufficient when the yacht stays in the marina for extended periods.