A monitoring system has a polyphase distribution transformer monitoring (PDTM) device that interfaces with electrical conductors electrically connected to a transformer. The PDTM device measures a current and a voltage in each of the electrical conductors simultaneously. Further, the PDTM device has a plurality of free-moving satellite current sensors coupled to flexible cables, and each current sensor is undetached from the other current sensors. Additionally, each satellite current sensor is electrically coupled via a current cable to at least one connector on a control box for which to deliver data indicative of current sensed by the current sensors and each current cable is paired with one of a plurality of voltage cables, and each current cable and voltage cable pair is coupled to the at least one connector. In addition, the system has a processor that calculates values indicative of power corresponding to the transformer based upon the currents and the voltages measured and transmit data indicative of the calculated values.