0. An 'appliance' (white goods) and ITE have similar, but not same, requirements for Class II and Class III equipment.
1. Unknown, and your definition is incomplete. Dependent on rating of the power source to the Class III device. SELV output rating does not imply Class III equipment. By definition, for non-medical equipment, SELV is considered safe to touch, but is not necessarily Class III. Leakage through body not necessarily considered for Class III device, but for touch-current, reference the human-body models and test methods for leakage in IEC60950-1 and IEC60335-1. 2. Non sequitur. Both provide galvanic isolation. Step up/down is simple matter of turns ratio of other than 1:1. A mains isolation transformer, depending on the ground reference, can be used for - float the equipment connected to the secondary to prevent a neutral connection to ground - noise mitigation - leakage current mitigation - controlling mains output impedance - door stop 3. Unknown, as Class III products do not necessarily have the built-in protective construction required of Class I and II equipment. By definition, Class III equipment has no earthing; mostly because the intent is that power is provided by a Class II source, which implements DI, thus no protective earth requirement. For a transformer winding intended to source a Class III construction, the unit would have to meet inherently limited and inherently short-circuit proof requirements per IEC61558-1 and -2-6 and/or -2-16, and the outputs would have to be floated and insulated from ground, and the capacitance of the windings would have to be low enough to limit the touch current to any exposed metal surface. In North America, the transformer should be assessed per UL5085-3/CSA No.66.3. Brian From: Vincent Lee [mailto:000008e6c8d35910-dmarc-requ...@ieee.org] Sent: Wednesday, March 07, 2018 7:17 PM To: EMC-PSTC@LISTSERV.IEEE.ORG Subject: [PSES] Isolation Transformer & Class III electrical protection Hi all, Good day, (1) If Class III electrical protection is defined as appliance with voltage output less than SELV (30Vrms based on IEC 60950 IT equipment), so can a laptop AC - DC power adaptor with output rating 19Vrms, 2.37A be considered as Class III, given that output current, 2.37A is much more than 10mA Threshold "Let-Go" current ? (2) How does Isolation Transformer different from the usual Step-Down Voltage Transformer? (3) And how does Isolation Transformer helps to achieve Class III electrical protection as stated in page 3 of https://www.excelsys.com/wp-content/uploads/2011/09/ApplicationNoteAN1102-ClassIvsClassII.pdf Hope to hear from you soon. Thank you & have a nice day ahead. Vincent Regards, Vincent - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <emc-p...@ieee.org> All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://www.ieee-pses.org/list.html (including how to unsubscribe) List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <sdoug...@ieee.org> Mike Cantwell <mcantw...@ieee.org> For policy questions, send mail to: Jim Bacher: <j.bac...@ieee.org> David Heald: <dhe...@gmail.com>
