Perception of chassis leakage current

The issue of chassis leakage currents flowing through areas on the surfaces of patients' bodies is again being discussed, probably because of increasing acceptance of International Electrotechnical Commission (IEC) Standard 601-1, the use of more instruments with computational capability but with generally higher chassis leakage currents at the bedside, the absence of evidence that the 500-microampere chassis current limitation of IEC 601-1 has been harmful, and the lack of data to substantiate the lower limit currently applied in the United States. Reported relevant experiments have not attempted to duplicate the conditions existing for the situations of concern--an open ground, a person touching the chassis of the device that has an open ground condition, and this person then touching the patient; or a grounded patient touching an ungrounded chassis. In terms of perception of current, the patient touching an ungrounded chassis and being grounded would generally be the more sensitive, since the conductive path of just one person, the patient, is involved. A small test was conducted that simulated a person touching a chassis with an open ground wire and then touching a patient. The results did not confirm previous findings in another study that currents ranging from 261 to 500 microamperes caused pain. They were closer to those of a study of perception of 60-Hz current, in which similar currents elicited only perception.