Hi Rich:
Another type of uninsulated power supply that I have seen is what I think may be called an "off-line switcher" (I may be mistaken about the name). In any event, there is a class of power supply that does not uses a transformer at all, and does not have safety insulation between the primary and secondary. Most of the ones I have seen are for comparatively low-power applications. Joe Randolph Telecom Design Consultant Randolph Telecom, Inc. 781-721-2848 (USA) <mailto:[email protected]> [email protected] <http://www.randolph-telecom.com> http://www.randolph-telecom.com From: Richard Nute [mailto:[email protected]] Sent: Wednesday, February 16, 2022 5:36 PM To: [email protected] Subject: Re: [PSES] Numbers of insulation layers in transformer (IEC62368) Hi Joe: Isn't it also true that if the secondary has no accessible conductive parts, and the entire enclosure meets the requirements for reinforced insulation, then no safety insulation at all is required in the transformer? In this case, wouldn't the entire contents of the enclosure would be treated as though they are 230 Vrms AC mains. Yes! Thanks for describing this alternative. In this case, the transformer has one layer of tape which is functional insulation. Or none, in which case the transformer is an auto-transformer. Best regards, Rich From: Joe Randolph <[email protected] <mailto:[email protected]> > Sent: Wednesday, February 16, 2022 2:22 PM To: [email protected] <mailto:[email protected]> ; [email protected] <mailto:[email protected]> Subject: RE: [PSES] Numbers of insulation layers in transformer (IEC62368) Hi Rich: You said the following: If the secondary has no accessible conductive parts, then the insulation between the secondary and accessible surfaces (whether or not conductive) is "supplementary insulation": transformer can have one insulation layer, basic. (This is uncommon construction and will likely be not acceptable to many certification houses.) Isn't it also true that if the secondary has no accessible conductive parts, and the entire enclosure meets the requirements for reinforced insulation, then no safety insulation at all is required in the transformer? In this case, wouldn't the entire contents of the enclosure would be treated as though they are 230 Vrms AC mains. I realize that this might seem like an unlikely type of product, but I have seen such configurations used in the past, it seemed okay to me. Joe Randolph Telecom Design Consultant Randolph Telecom, Inc. 781-721-2848 (USA) [email protected] <mailto:[email protected]> http://www.randolph-telecom.com From: Richard Nute [mailto:[email protected]] Sent: Wednesday, February 16, 2022 5:09 PM To: [email protected] <mailto:[email protected]> Subject: Re: [PSES] Numbers of insulation layers in transformer (IEC62368) Hi Amund: Since the unit does not have grounding/earthing, it is therefore double-insulated with respect to the input 230 volts (and must bear the double-insulated symbol). This requires all accessible conductive parts and accessible surfaces to be double-insulated from the 230 volts. If the secondary circuit has any accessible conductive parts (e.g., metal antenna), then the secondary must be double-insulated from the 230 volts: transformer must have two insulation layers, basic and supplementary. (This is the most common construction.) If the secondary has no accessible conductive parts, then the insulation between the secondary and accessible surfaces (whether or not conductive) is "supplementary insulation": transformer can have one insulation layer, basic. (This is uncommon construction and will likely be not acceptable to many certification houses.) Good luck, and best regards, Rich From: Amund Westin <[email protected] <mailto:[email protected]> > Sent: Wednesday, February 16, 2022 1:02 PM To: [email protected] <mailto:[email protected]> Subject: [PSES] Numbers of insulation layers in transformer (IEC62368) Do I need one or two insulation layers (tape) between the primary and secondary windings? Can find an absolute answer in the standard IEC62368. Product: Input 230VAC Secondary 24VDC for other Low volt circuits No grounding /earthing No cable outputs Plastic enclosure Radio HUB product Thanks. Best regards Amund - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. 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