I also agree that the headphones are a patient connection.
Hi, Its been a while since I looked at UL 544, but a few comments. 1. Headphones are an applied part (UL2601-1) or patient connection (UL544). They come into direct contact with the patient. You can argue that they are an ordinary patient connection (Clause 2.18 of UL544). But, it is still a patient connection. The limit is 50 uA for ordinary patient connection. 2. How long is this product going to be in the market? UL 544 goes away on 1/1/2003 for new products and 1/1/2005 for all products. You might be better off going to UL2601-1 now. In UL2601-1 this type of patient connect is Type BF. The patient leakage current limit is 100 uA in normal condition and 500 uA in single fault condition. 3. Call UL. Maybe I missed some "out" in UL544. Ned Devine Entela, Inc. Program Manager III Phone 616 248 9671 Fax 616 574 9752 e-mail ndev...@entela.com -----Original Message----- From: me...@aol.com [mailto:me...@aol.com] Sent: Friday, March 24, 2000 3:36 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 ______________________________________________________ Get Your Private, Free Email at http://www.hotmail.com ------------------------------------------- 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
