A system and method for monitoring the health of a heater connected to a power supply by a power cable that includes a first power lead conducting an inlet current having an inlet current direction, and a second power lead conducting an outlet current having an outlet current direction opposite to the inlet current direction. The power cable passes through a center region of a toroid core one or more times, and a secondary winding on the toroid core is configured to induce a secondary voltage indicative of a difference between the inlet current and the outlet current, which defines the leakage current. The system includes a prognostic processor that is configured to calculate a heater health indication based on the secondary voltage, which is indicative of the heater health.