Peter, We are checking with Dupont's expert to see if what we are concerned now for the 600V or 300V system refers to the input voltage (primary winding voltage) only. Perhaps you are right, thanks. But if you can cite any good source to support this, that would be much helpful to us.
For the construction guidlines, please let me know which UL standard we should follow. I just contacted UL Hong Kong that they have no idea on it. Initially, they suggested UL-1585 for the design standard for microwave oven transformers. But they informed me that they have made a mistake and even they would need time to check. Perhaps you have some idea, right? Robin Chan. > >Dear Robin, > >If I'm not mistaken the 300 V or 600 V rating for Insulation Systems >per UL1446 is for primary supply voltage and not for the maximum >voltage in any winding. > >You state that the transformer is being designed for a 200 C rating. >Remember that you need only comply with UL1446 if your >transformer winding temperatures exceed the Class A insulation >system permitted temperature rises in the Microwave and/or >applicable transformer standards under normal and abnormal >conditions. > >Once you have determined that you need a higher than Class A >insulation system, best and cheapest way to obtain a UL1446 >compliant system is to have UL conduct Sealed Tube Testing on >your system and an adopted system from Nomex manufacturer (I >believe it is EI Dupont) using identical major insulation system >parts (ground insulation is a major part). Nomex manufacturer will >be very happy to give you a letter authorising UL the use of the >information in their file to grant your company Recognition for your >system employing their major insulation materials. > >Best Regards, > > >> Dear everybody, >> >> We are now designing a transformer for microwave oven. Here is the >> basic spec, >> >> input voltage: 120V rms >> output voltage: 2300V rms >> Thermal class: 200C >> >> We are facing the problem that we need to be compliace with UL1446 >> and UL 1585. They specify that all ground insulation need to be at >> least 5 mil Nomex for a 600V system. Then for 2300V system, by >> scaling the thickness of Nomex, do we need to increase the thickness >> to 18-20mil Nomex. Well, we can use Nomex at that thick but the cost >> of the whole unit becomes very high, any comments? >> >> Robin Chan. >> >> ---------------- >> email: [email protected] >> >> --------- >> This message is coming from the emc-pstc discussion list. >> To cancel your subscription, send mail to [email protected] >> with the single line: "unsubscribe emc-pstc" (without the >> quotes). For help, send mail to [email protected], >> [email protected], [email protected], or >> [email protected] (the list administrators). >> > > ______________________________________________________ Get Your Private, Free Email at http://www.hotmail.com --------- This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to [email protected] with the single line: "unsubscribe emc-pstc" (without the quotes). For help, send mail to [email protected], [email protected], [email protected], or [email protected] (the list administrators).
