Threshold of sensation for 60-Hz leakage current: results of a survey

Canadian regulations have set a limit of 100 microA on leakage currents permitted to flow from patient-applied parts of an electromedical device under single-fault conditions, while international standards, such as International Electrotechnical Commission (IEC) 601-1, have set the limit of 500 microA under the same conditions. Canadian agencies have suggested that national standards for electromedical devices should harmonize with widely used international standards by increasing the leakage current limit to 500 microA. The authors investigated the question of whether 500 microA would compromise safety, or would be unpleasant or painful for the patient. A survey was conducted on the reactions of 95 adult volunteers to 60-Hz alternating currents ranging from 10 to 500 microA applied through typical ECG electrodes to determine the level at which these volunteers felt a distinctly uncomfortable or painful sensation. Results of this survey confirm that 500 microA currents are more than sufficient to induce pain in healthy adult volunteers, and that currents greater than 100 microA can evoke a definite sensation. Based on these findings, the authors recommend that the maximum allowable leakage current for patient-applied parts under single-fault conditions should not exceed 100 microA.