SM seires RCCBs apply to in AC circuit of frequency of 50/60Hz, rated voltage up to 415V, rated current up to 80A. It is mainly used as an indirect contact protection for human. It also can be used to prevent against the fire danger caused by earth fault current owing to equipment insulation damage. When the protective measures of the electric shock are out of work, the RCCB whose rated residual operating current less than 30mA can serve as the supplementary protection for an direct contact, but it can誸 be used as the sole direct contact protection. They conform to IEC61008.