One speaks about galvanic insulation between two directly close electronic circuits when the current cannot circulate directly between these two circuits.

• a Transformateur allows a galvanic insulation between the primary education and the secondary because it does not have there connection between them.
• a Optocoupleur allows a galvanic insulation between the transmitter and the receiver because the transmission of information is done thanks to a luminous flow.

• a auto-transformer ensures no galvanic insulation between the primary education and the secondary.

• If two electronic circuits have a joint mass, they, by definition, are not galvanically insulated. The mass is not directly connected has a functional point of the circuit but it can be connected to one moment there or another (handling error, defective material,…). For this reason, the transformers of insulation do not provide a ground/mass.