Abstract: A double insulating protected system for use in coupling an instrumentation system to a remote power source so as to test an experimental system without posing life-threatening hazards. Connection between the instrumentation system and power source is accomplished by a pair of cascaded isolating transformers, with the connections between the two transformers being inaccessable, such as by a separate housing. The instrumentation system equipment ground is coupled to the experimental system equipment ground via a drain conductor so as to reference the former system to the same potential as that of the latter. The system provides a double insulation system such that a primary-to-secondary, primary-to-frame, or secondary-to-frame fault occurring in either of the transformers, or similar faults in the instrumentation system, will not result in a life-threatening situation to the system user.