Symbol 5156 from IEC 60417 - Title/Meaning: Transformer Function/description: [To identify switches, controls, connectors or terminals which connect electrical equipment to the mains through a transformer. It can also be used on an envelope or a case to indicate that it contains a transformer (e.g. in the case of a plug-in device).]
Additional information: 
The symbol may be used without the vertical bars to indicate ""separating transformer"" defined in IEC 61558-1.
To indicate a fail-safe function, the letter F may be used adjacent of the symbol
Published in: IEC 60417 database
Own work using: iso.org/obp/graphics/grs/3a2c370d-d082-476f-a2ae-b3e47b77a6e1 200.png
Vectorization:  Mrmw