Hi Amund:
In 60950-1 (and I believe similarly in 62368-1), there is no specific requirement to have two layers of insulation. A single layer is okay to use if it meets the performance requirements of so-called "double insulation." The term "reinforced insulation" is used in 60950-1 to refer to this distinction. I'm short on time today, but I'll try to elaborate further later. 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: Amund Westin [mailto:[email protected]] Sent: Thursday, February 24, 2022 1:27 PM To: [email protected] Subject: [PSES] SV: [PSES] SV: [PSES] Numbers of insulation layers in transformer (IEC62368) A Class II or double insulated electrical appliance (bear the double insulation symbol), is it required to have a transformer with 2 insulating layers? Or is one layer in transformer ok, if the plastic enclosure is giving enough insulation, thus in total you will have 2 layers of insulation? Ref. 62368-1 product (AC powered WiFi HUB). No cabling/wiring on secondary side. Cheers! BR Amund Fra: Joe Randolph Sendt: 18. februar 2022 05:09 Til: [email protected] <mailto:[email protected]> Emne: Re: [PSES] SV: [PSES] Numbers of insulation layers in transformer (IEC62368) Hi Amund: In general, a safety lab does not spend time thinking about hypothetical scenarios. They usually focus on simply complying with the requirements of the applicable safety standard, which in this case is 62368-1. I'm still relatively new at using 62368-1, but I have lots of experience using 60950-1. While there are differences in how the two standards approach the issue of safety for 230 Vac mains, I think the underlying philosophy is the same: 1) 230 Vac mains should not be "accessible" to ordinary users 2) 230 Vac mains should not become "accessible" without a double-fault condition There are lots of ways to meet these criteria. Key to both of the above criteria is the definition of "accessible." The method for making sure that a 230 Vac circuit is not accessible is to carefully apply the definition of "accessible" in the standard. Safety standards typically define "accessible" with various criteria including various specialized probes that simulate a human finger, along with various criteria regarding anticipated use. I'm not sure how 62368-1 defines accessibility, but in 60950-1, a 230 Vac circuit is considered to be accessible if it can be touched by the specified probes without the use of a "tool" (such as a screwdriver). Further, even if a "tool" is required to be able to touch a 230 Vac circuit, that circuit is considered to be accessible if the user is instructed to use a tool to access the area, such as a battery compartment. I don't know the details of the removable part on the product in question, but perhaps the above considerations will help you evaluate the available options. Joe Randolph Telecom Design Consultant Randolph Telecom, Inc. 781-721-2848 (USA) [email protected] <mailto:[email protected]> http://www.randolph-telecom.com <http://www.randolph-telecom.com/> From: Amund Westin [mailto:[email protected]] Sent: Thursday, February 17, 2022 2:57 AM To: [email protected] <mailto:[email protected]> Subject: [PSES] SV: [PSES] Numbers of insulation layers in transformer (IEC62368) Thanks, guys! I have not received a fully explanation from the safety lab, but I assume they are concerned about this: - With only one insulation layer between Prim/Sec winding in the transformer, a fault in the insulation tape will result in 230VAC in the secondary circuits. OK, but there are no cable interfaces on the secondary side and no conductive parts. The entire enclosure is flame category V-1 or V-0. But one part of the enclosure is a little piece that is pressed onto the main part of the enclosure. This little part can be demounted, and since the product is plugged into a 230VAC socket that is located 20 cm above the floor, a child could manage to remove this little part and access the secondary circuit (now 230VAC) by its fingers. I guess this is the reason for requiring two layers in the transformer. Or make it impossible to remove this part which can give access to secondary circuits. Best regards Amund Fra: Richard Nute Sendt: 16. februar 2022 23:09 Til: 'Amund Westin' <[email protected] <mailto:[email protected]> >; [email protected] <mailto:[email protected]> Emne: 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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