7.15.2 - Transformers

Transformers are used more widely in the supply system than in the installation itself. The link between the primary and secondary windings of a double wound transformer is magnetic, not electric, so there is no electrical connection with the supply system, or with its earthing system, from a circuit fed by the secondary winding of a transformer. This loss of earthing may be an advantage where electrical separation is required, for example, where an electric shaver in a bathroom is fed from the secondary winding of a transformer (see {5.8.4}).

Step-up transformers must not be used in IT systems. In systems where they are permitted, linked multipole switches must be provided so that the supply is simultaneously disconnected from all live conductors, including the neutral.