Hi Camille: Now that you've clarified what you want, I can answer your questions. The IEC 60664 clearances are for 2000 meters altitude. The standard includes altitude factors for both lower and higher altitudes. Basically, the electric strength of a clearance is directly proportional to air density (or air pressure). The more dense the air (the lower the altitude), the higher the electric strength (and vice versa). So, according to 60664, for the same electric strength at 3000 meters, the 2000 meter clearance distances must be increased by a factor of 1.14. Since your standard, 60044, has clearances for 1000 meters, then for 3000 meters, the clearance distances must be increased by a factor of 1.35. (See Table 8 and Annex F in 60664-1, ed 2.) For example, if the 60044 requirement is 2 mm (at 1000 meters), then 2 x 1.35 = 2.7 mm for 3000 meters. Since clearance requirements are for minimum distances, increasing the clearances for 3000 meters means the equipment still complies with the 60044 clearance requirements. So, there is no conflict in applying the 60664 altitude correction factors to the requirements of 60044. IEC 60950 clearances are for 2000 meters. >From time to time, there is talk about increasing the requirements to 3000 meters as the equipment is indeed used at 3000 meters. However, the 2000 meter clearances are for worst-case (purely inhomogeneous) fields and are rounded upward, so the resulting margin is more than the 1.14 factor. This explains why there are no clearance failures at 3000 meters in 60950 equipment. Best regards, Rich
From: [email protected] [mailto:[email protected]] On Behalf Of Camille Good Sent: Thursday, March 09, 2006 6:15 PM To: John Woodgate; [email protected] Subject: Re: Basic questions about IEC 60664 series > Please tell us about the 'not clearly defined' issue. It isn't safe to > say 'yes, use IEC 60664' without knowing the circumstances. Well, the question was both specific & generic, if that makes any sense. And I did know that whatever a final product standard calls out will supersede what is in the reference standards. In the specific case, I'm currently looking at a couple of standards in the IEC 60044 series. Both standards specifically say they are assuming a maximum altitude of 1 000 meters, but both also have a clause saying "For installation at an altitude higher than 1 000 m, the arcing distance under the standardized reference atmospheric conditions shall be determined by multiplying the withstand voltages required at the service location by a factor k in accordance with figure 1. NOTE As for the internal insulation, the dielectric stren! gth is not affected by altitude. The method for checking the external insulation shall be agreed between manufacturer and purchaser." The product specs we (my colleagues & I) are looking at call out rated altitudes of 2 000 or 3 000 meters for different products, and the correction factors in the IEC 60044 standards do go that high, so we are covered by the end-product standard, I think. However, while some of us were sitting around discussing this standard, someone else mentioned that 60950 had only specified ratings & test conditions for up to 2 000 m**, and he had always wondered what was going on with power supply manufacturers who claimed their power supplies complied with 60950 & were good up to 3 000 m. So I thought I would ask the question about use of 60664 in a general sense as well. ! **Note: I am not familiar with 60950 myself and do not have a copy readily available where I can check this assertion, so hopefully the list members will not be too strident in their corrections if this statement turns out to be in error. :) Many thanks for the assistance, -Camille Good Portland, Oregon John Woodgate <[email protected]> wrote: In message <[email protected]>, dated Wed, 8 Mar 2006, Camille Good writes >1) My understanding of the interrelation between different IEC >standards is that IEC 60664-1, Insulation coordination for equipment >within low-voltage systems, is considered to be a basic standard for >creepage &! amp; clearance requirements, and while some end-product standards >(like 61010 & 60950) might have insulation requirements specific to the >end-product environment or application, IEC 60664 is the beginning >point for the insulation, creepage & clearance requirements. Is that >understanding correct, or am I missing something? Yes. > >2) If I am looking at an IEC end-product standard, and there is an >insulation issue that is not clearly defined, is it acceptable to look >at the IEC 60664 series for guidance? Please tell us about the 'not clearly defined' issue. It isn't safe to say 'yes, use IEC 60664' without knowing the circumstances. -- OOO - Own Opinions Only. Try www.jmwa.demon.co.uk and www.isce.org.uk 2006 is YMMVI- Your mileage may vary immoderately. John Woodgate - This message is ! from the IEEE Product Safety Engineering Society emc-pstc discussion list. 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