Abstract: A system for use in tracing and identifying each one of a group of AC circuits in a power distribution network without necessitating removal of power from live circuits and without adverse effect on normal circuit operation. A simulated load is adapted to be coupled to any specific one of the live circuits being traced within the power network, and is operative to provide a DC current in the particular circuit in addition to the normal AC current component. A test device is adapted to be coupled sequentially to each circuit breaker or other circuit protective device normally included in each branch circuit and uniquely identifies the circuit being traced by sensing a DC voltage drop solely across the small but finite resistance of the protective device within that circuit. Means are provided to protect the sensitive DC test apparatus from damage due to inadvertant contact with the high AC voltages present in the network.