An electronic instrument designed to measure and assess the electrical characteristics of a power line receptacle (e.g., an electrical wall receptacle or electrical wall socket). It is typically a plug-in device that can detect open (e.g., ground, live, neutral) lines and inverted connections (e.g., live on neutral); it usually includes a display and/or visual and audible alarms to indicate correct/faulty wiring and open connections. The device is used to assess the electrical characteristics of the most common healthcare facility electrical wall receptacles; some can also determine the tripping current of ground fault circuit interrupters by injecting a variable leakage current.