An apparatus includes power circuitry and hazard detection circuitry connectable to a multi-conductor cable. The power circuitry transfers electrical power from a power-sourcing equipment (PSE) to a powered device (PD) over the multi-conductor cable. The hazard detection circuitry senses an electrical characteristic of the multi-conductor cable and generates a detection signal indicating whether a potentially hazardous abnormal operating condition exists in the multi-conductor cable based on the sensed electrical characteristic. Examples include short-circuit detection circuitry which detects a hazard-producing short-circuit connection between sets of conductors that can cause a “stacking” or additive combining of PSE output voltages, and hot-cable detection circuitry detecting the presence of full operating voltage on the cable under abnormal conditions.