Ground mounted 11 kV/433 V distribution transformers have a high level of reliability; approximately 100 fail in the UK per year out of a total of 160 000. The provision of protection by the traditional means of fuses or circuit-breakers at the transformer appears to be an unnecessary expense. Consequently consideration has been given to the solid connection of transformers to the network. The major disadvantage of this approach is that the protection on the outgoing cable circuits from primary 33/11 kV substations may not detect certain transformer or busbar faults on the low-voltage fuse gear. The solution under consideration is the provision of current transformers on the 11 kV side of the transformer to energise a simple time-delay fuse protection circuit. This circuit, on operation, will trip a fault throwing circuit connected to one phase of the 11 kV supply of the transformer. The closed switch will permit earth fault current to flow of sufficient magnitude to operate the protection on the circuit-breaker controlling the circuit concerned at the primary substation. Designs of fault thrower using vacuum or SF6 switches are described with the protective circuitry and details of proving tests carried out. Consideration has also been given to the mounting of the fault thrower on the transformer and the means of isolation.