One hopes that the 4C difference would be accounted for in the temperature limits imposed by most standards. If I found a spot within 4C of a limit, I'd take a harder look at things anyway.
If it's 35C at MSL, what's the air temperature at 2000m? Perhaps it's down by more than 4C. Ralph McDiarmid, AScT Compliance Engineering Group Xantrex Technology Inc From: [email protected] [mailto:[email protected]] On Behalf Of Paul Lovell Sent: Friday, September 07, 2007 2:51 AM To: [email protected] Subject: RE: Max. ambient temperature On a slightly different track, what about the thermal effects of altitude? 60950-1 and 60601-1 are deemed to 'work' up to 2000m elevation, but most of the labs (I would assume) are at, or close to, sea level. However, it's well known (in the NEBS world at least) that the thinning of the air will lead to increased internal temperatures at a rate of approx 1C per 500m elevation, so a device running in a 25C ambient will be about 4C hotter inside (ie windings etc) at 2000m than at sea level. I've wondered for some time why the safety standards don't take this into account although they make allowances for minimum clearance distances at higher altitude. Is this just an error of omission or is the effect too small to be significant? I remember in my BSI Testing days that we would occasionally have products which only just passed the heating test without considering the effect this might have at 2000m: it just wasn't 'on the radar'. I'd be interested in any thoughts you might have on this. Best regards, Paul Lovell Group Compliance Manager Huntleigh Technology Tel: +44 (0)1582 745891 Mob: +44 (0)791 956 5599 From: [email protected] [mailto:[email protected]] On Behalf Of John Woodgate Sent: 07 September 2007 10:08 To: [email protected] Subject: Re: Max. ambient temperature In message <1f5308c5923f3b4daa51d189bf25500602978...@edgmsmail01.eu.thmulti.com>, dated Fri, 7 Sep 2007, Carpentier Kristiaan <[email protected]> writes: >Which IEC standard gives this classification? For example, IEC 60065. However, the information is not obvious and there is an error, which I will take up with the relevant committee. 4.1.3 gives the upper ambient temperature limit as 35 C 'unless otherwise specified'. In the 'conditions applicable' of Table 3, the explanation of '35 C for temperate climates and 45 C for tropical climates' is given, but attributed in error only to reference 'a' in the table, which is 'metallic enclosures'. This was corrected in Corrigendum 1, where metallic enclosures were given reference 'b', but now there is no reference 'a' in the table at all! It should be added to the headings of the columns 'Normal operating conditions' and 'Fault conditions'. -- OOO - Own Opinions Only. Try www.jmwa.demon.co.uk and www.isce.org.uk There are benefits from being irrational - just ask the square root of 2. John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. 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