The encapsulated isolation transformer has its windings covered in heat-cured epoxy resin to reduce noise and prevent ingress of moisture and dust. Where for the non-encapsulated model has visible bare windings which are subject to dust and moisture.
Encapsulated - E14/36/2 & E14/48/2
Non Encapsulated - E14/36/3 & E14/48/3
For further information see link https://www.clipsal.com/search?q=E14