SmartlockPro® Extra-heavy duty industrial grade self-test GFCI isolated ground receptacle. NEMA 5-20R without wallplate. Patented bridge contact design provides individual sets of contacts for GFCI receptacle face and downstream receptacles; no power will be delivered to receptacle face if improperly wired (line-load reversed). Improved immunity to high frequency noise reduces nuisance tripping. Advanced electronics provides superior resistance to electrical surges and over-voltages. Low-profile design is easy to install in all electrical boxes.