Good Day - First, why are you using UL544? Why not use UL2601, based on IEC601-1 with US deviations? Beware, UL544 & UL187 may be used until Jan 1 2003, after that use of UL2601 will be mandatory. Also, As of Jan 1 2005, all Listed, Classified and Recognized medical and dental products, where UL544 or UL187 was used to evaluate the product, must comply with UL2601-1 (direct quote from UL2601).
This may shed some light - definitions from UL2601 Applied Part: Entirety of all parts of equipment including the patient leads which come intentionally into contact with the patient to be examined or treated. For some equipment, particular standards may consider parts in contact with the operator as an applied part. Enclosure: Exterior surface of equipment including: - all accessible metal parts, knobs, grips and the like - accessible shafts - for the purpose of tests, metal foil, with specified dimensions, applied in contact with parts of the exterior surface made of material with low conductivity or made of insulating material (i.e. insulated / double insulated enclosures) Patient Circuit: Electrical circuit of which the patient forms a part. F-Type applied part: Applied part isolated from all other parts of the equipment to such a degree that the patient leakage current allowable in single fault condition is not exceeded when a voltage equal to 1.1 times the highest rated mains voltage is applied between the applied part and earth. Type B equipment: equipment providing a particular degree of protection against electric shock, particularly regarding: allowable leakage current, reliability of the protective earth connection (if present) Type BF equipment: Type B equipment with an F-Type applied part. Allowable leakage currents: Enclosure Leakage: N.C. (normal condition) .1 milliamps, S.F.C. (single fault condition) .5 milliamps Same limits for Type B or BF equipment Patient Leakage: Same as Enclosure Leakage for both Type B or BF equip. (Taken from Table IV of UL2601, other leakage currents of concern are Earth Leakage, Patient Aux Current, Patient Leakage Current with Mains Voltage Applied) With regards to your equipment, depending on your design, I would say it is either a Type B or Type BF. I would lean towards the Type B. It would be VERY wise to confer with the engineer at your chosen NRTL (domestic National Recognized Testing Lab). These are the people you need to convince on the classification of your product and your chosen route to compliance. I hope this didn't confuse you any more, I know it can be and that's why I do not hesitate to contact the engineers at UL from time to time. I have found the ones I deal with helpful and very understanding and easy to work with (this is not intended to promote UL, only my opinion of them). -----Original Message----- From: me...@aol.com [mailto:me...@aol.com] Sent: Friday, March 24, 2000 2:36 PM To: jjuh...@fiberoptions.com; m.r...@ieee.org; emc-p...@majordomo.ieee.org Subject: UL544 Leakage Limits Patient Equipment* Most esteemed colleagues, we are looking for your professional opinion on a UL 544 leakage limit (I think you will find this interesting): 1. This particular product uses a UL 544 evaluated direct plug in power supply with outputs to the patient care equipment. In this case it is a diagnostic unit that sends an audible tone to headphones (audiometer). The plug in power supply Conditions of Acceptability indicate the outputs are "not evaluated for patient leads" (i.e. applied parts"). 2. Table 42.1 of UL 544 specifies leakage limits. "patient connection" footnote "a" references testing of "patient leads (applied parts)" connections. There is no written definition for "patient leads" or "applied parts" in UL544. As such NFPA 99 supplements UL 544 as it draws from the NEC and NFPA 99 (referenced in UL 544): NFPA 99 defines the US definition of "Patient Lead" = "A deliberate electrical connection that can carry current between an appliance and patient. It is not intended to include adventitious or casual contacts such as a push button, bed surface, lamp, hand held appliance, etc." 3. As the headphones of this audiometer are clearly not "deliberate electrical connections" we conclude these are not "patient leads (applied parts)" which would not fall under the limits for "patient connection" limits per 544. The applicable limits would be as defined under "enclosure or chassis" "grounded " or" double insulated".... Now be careful not to jump to a conclusion yet..... You might say "enclosure or chassis?", but if you examine this, you will find the footnotes reference UL 544's Enclosure definition: "Enclosure = That external portion of an appliance that serves to house or support component parts, or both. Enclosure of patient care equipment likely to be contacted by a patient include, for example, bedside monitors, bed frames, dental chairs, and examination stands." Our conclusion: Due to the US definition of "patient leads (applied parts)", the earphones of an audiometer (patient care equipment) are subjected to the leakage current limits for "enclosure or chassis", and not the limits of "patient connection". For this particular application, we conclude that based on the C of As, the output of the power supply has already been evaluated for "enclosure or chassis" leakage limits. Your Thoughts??? Drew PS: If you care to look, CSA supports this position in that 50uA is related to "cardiac tissue" limits only. See Appendix A of CSA 22.2 125 (500uA). ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Jim Bacher: jim_bac...@mail.monarch.com Michael Garretson: pstc_ad...@garretson.org For policy questions, send mail to: Richard Nute: ri...@ieee.org ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Jim Bacher: jim_bac...@mail.monarch.com Michael Garretson: pstc_ad...@garretson.org For policy questions, send mail to: Richard Nute: ri...@ieee.org
