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, Date sent: Thu, 10 Dec 1998 20:05:09 +0800 From: Robin Chan <ro...@alumni.cuhk.edu.hk> Organization: The Chinese University of Hong Kong To: emc-p...@ieee.org Subject: UL system for Microwave oven transformers Send reply to: Robin Chan <ro...@alumni.cuhk.edu.hk> > 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: ro...@alumni.cuhk.edu.hk > > --------- > This message is coming from the emc-pstc discussion list. > To cancel your subscription, send mail to majord...@ieee.org > with the single line: "unsubscribe emc-pstc" (without the > quotes). For help, send mail to ed.pr...@cubic.com, > j...@gwmail.monarch.com, ri...@sdd.hp.com, or > roger.volgst...@compaq.com (the list administrators). > PETER S. MERGUERIAN MANAGING DIRECTOR PRODUCT TESTING DIVISION I.T.L. (PRODUCT TESTING) LTD. HACHAROSHET 26, P.O.B. 211 OR YEHUDA 60251, ISRAEL TEL: 972-3-5339022 FAX: 972-3-5339019 E-MAIL: pe...@itl.co.il Visit our Website: http://www.itl.co.il --------- This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to majord...@ieee.org with the single line: "unsubscribe emc-pstc" (without the quotes). For help, send mail to ed.pr...@cubic.com, j...@gwmail.monarch.com, ri...@sdd.hp.com, or roger.volgst...@compaq.com (the list administrators).
