The Hazard Compensator: A New Technique of Leakage Hazard Reduction in Ungrounded Systems

Abstract

Shock hazards of capacitive leakage in isolated electrical systems are only recently being well recognized. Dangers are increasing through growth of heart surgery and use of intracardial probes and electrodes.

Hazard reduction by better system design now produces diminishing returns, and does nothing for connected equipment leakage. Typical total system leakages are still 100 microamps or more on latest designs, vs fibrillation levels of about 20 microamps for direct myocardial contact.

The Hazard Compensator uses a new approach, accepting leakage existing in the system, but reducing its shock hazard on accidental body contact. It drives current from ground to line equal to leakage current flowing from line to ground. This forms a closed current loop, with system leakage supplied by the compensator, thus excluding accidental body paths from the leakage loop.

Already in service, the device is applied one per system, single-circuit type where system changes are small, or multi-circuit to accomodate to changes in system leakage. It can compensate for connected equipment leakage, and be module-mounted on equipment to remove its individual hazard. Typical 20:1 hazard reduction now makes 20 microamp total system hazard index attainable.