It may seem strange that not all transformers are classed as safety transformers but there are reasons for this. The U.K. mains power supply is of course referenced to earth, but many others are not and the use of unearthed equipment on a U.K. mains supply poses basic dangers. Safety transformers, or isolation transformers, remove this risk by producing output power that is completely independent from the U.K. mains norm, eliminating any potential current path between live and earth, i.e. electric shock. This means, in theory at least, that it would be possible to touch a live wire while standing on the ground with no adverse effects, but don't try this at home, folks! The primary and secondary circuits of a safety transformer are galvanically isolated and the transformer will feature class II double insulation. It may also incorporate a circuit breaker. The choice of a safety transformer involves the usual considerations of input supply and the required output voltage and current requirements. Some offer double outputs or a range of different output voltages. Step-down and step-up models are available. Some are suitable for chassis mounting and others are made to fit a standard DIN rail.