Altitude

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drcampbell said:
It's certainly better than not derating at all, but I wouldn't say it's "conservative", just adequate. At 3000 m altitude, there are 26% fewer air molecules in a given volume of air than at sea level.
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While it's true that the air is thinner (less dense) than compared to sea level. Most electronics are designed to operate to at least 1000 m without de-rating, therefore you only need to consider the difference from the reference altitude to your actual altitude. So, a piece of equipment with 1000 m service ceiling is only 2000 m above that.

It looks like you used density for you calculation to get 26% difference form 0 to 3000 m, but at 1000 m the difference in density is already over 9%. So, the difference from the normal operating condition (1000 m or less) is only 17%.

Also, not all heat is lost as a result of convection, some is lost through radiation and conduction. As I mentioned before lower ambient temperatures (typically 2C for each 1000 m) can also be used to your advantage.
 
Additional considerations

Additional considerations

Timbert said:
While it's true that the air is thinner (less dense) than compared to sea level. Most electronics are designed to operate to at least 1000 m without de-rating, therefore you only need to consider the difference from the reference altitude to your actual altitude. So, a piece of equipment with 1000 m service ceiling is only 2000 m above that.

It looks like you used density for you calculation to get 26% difference form 0 to 3000 m, but at 1000 m the difference in density is already over 9%. So, the difference from the normal operating condition (1000 m or less) is only 17%.

Also, not all heat is lost as a result of convection, some is lost through radiation and conduction. As I mentioned before lower ambient temperatures (typically 2C for each 1000 m) can also be used to your advantage.
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There are yet other factors that have not existed in the past. The Earth is being exposed to more UV frequencies such as UV " C." This has a very different impact on rapid heating of metals and anything organic for that matter. There is a lot more going on than what is presumed and its not straightforward or necessarily obvious as to what is underlying.
 
GeorgeB said:
I asked "highest elevation in UK", but (lacking research skills to check work) took first hit, https://en.wikipedia.org/wiki/Scafell_Pike without digging further. It says England.

The next hit was https://en.wikipedia.org/wiki/List_of_highest_points_in_the_United_Kingdom which gives Ben Nevis at 1344 metres (4409 ft.).

I'm just one of those dum sutherners from the Carolinas with the poorest school systems (and a wife who has a masters in information science who would flog me for my accepting Google and wikipedia alone ...)

Sweep me under the rug and let's get back to electrical issues ...
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Thanks for making me laugh. :happyyes:
 
StarCat said:
There are yet other factors that have not existed in the past. The Earth is being exposed to more UV frequencies such as UV " C." This has a very different impact on rapid heating of metals and anything organic for that matter. There is a lot more going on than what is presumed and its not straightforward or necessarily obvious as to what is underlying.
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If your PLC is exposed to sunlight the majority of the time you're not meeting Code. UV at best is a surface effect since by definition it is radiation. In panel heating we would be talking about bulk effects (Boltzmann/Planck aggregate model) so specific wavelengths are meaningless compared to the entire spectrum.


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GeorgeB said:
With (per Wikipedia) the highest point in UK being 978 metres, not a problem for your local jobs, was it ... ?
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BTW, UK isn't just England.

Oops! I see point has been addressed.
It's quite a common matter of confusion, even among Brits.
Oh well, VSDs can on 50Hz whichever part of UK in which they are located.
Your 60Hz transformers and motors may be less comfortable.
 
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Timbert said:
While it's true that the air is thinner (less dense) than compared to sea level. Most electronics are designed to operate to at least 1000 m without de-rating, therefore you only need to consider the difference from the reference altitude to your actual altitude. So, a piece of equipment with 1000 m service ceiling is only 2000 m above that.

It looks like you used density for you calculation to get 26% difference form 0 to 3000 m, but at 1000 m the difference in density is already over 9%. So, the difference from the normal operating condition (1000 m or less) is only 17%.

Also, not all heat is lost as a result of convection, some is lost through radiation and conduction. As I mentioned before lower ambient temperatures (typically 2C for each 1000 m) can also be used to your advantage.
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Two different issues. Within a PLC chassis they are kind of like computers. They rely on natural convection to get heat from the components out into the panel air space. They are designed to be packed densely so very little radiation off the front (frontal surface area is small, packed in on the sides). Little you can do about this. That leaves panel cooling itself. There are generally three panel killers. The first is not if but when the MCC environmental controls fail, if it ever had any, which is outside the panel. The second is using NEMA 4X-SS in direct sunlight. The third is using large heat sources like large VFDs, all CVTs of any size, and larger 10 kva+ transformers in the same enclosure without fans. Hoffmann has some excellent design guidelines that keep you out of trouble in terms of panel temperatures. It seems like overkill but it is conservative and works consistently.

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https://www.slideshare.net/Nawaraji...ude-consideration-for-electrical-power-system


2004_HighAltitude_Hillman-Blattau-Read-Only


Electronic components are affected by altitude. Some electronics are more prone than others to suffer failures as a result of low air density.

Power supply transformers, chokes and several wire-wound components use the dielectric attribute of air. . . it has its insulating effect.

The above link does explain how air affects electronic/electrical components.

The second white paper (the bottom one) explains how other solid state component failures are attributed to low air density at high altitude.

Note:

If the second link from the University of Maryland doesn't work, try copying the URL and typing it in your search engine. It is a copyrighted presentation that may not work in all platforms.

I'm still learning how to navigate through my new Linux machine.
 
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