Used mainly in residential service loads and where the power utilities require a load control. Starting at the design stage, self-protected transformers include protection elements against overvoltages, overloads, and elements to isolate it from the network in the event of internal or external failures. The following elements provide the self-protection: • Surge Protection Device SPD (lighting arrestor) • Protection fuse: Expulsion fuse or isolation link • Circuit breakers: Breaker or Magnex interruptor