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At first I thought it was a bad translation from Chinese to English, but it turns out that many data-sheets of kWh power meters mention a maximum altitude, usually below 2 or 3 km.

For example:

What exactly is the reason for the height (altitude) restriction?

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  • $\begingroup$ Are any components affected by pressure? $\endgroup$
    – Solar Mike
    Jun 30, 2023 at 4:57
  • $\begingroup$ @SolarMike Maybe, that's what I am wondering. As far as I knew they work by measuring the current via induction in small (single) coils around the main conductor. As for the voltage I have no clue (it should be more or less stable), but it's all electronics as far as I know, but obviously I must be missing something. $\endgroup$ Jun 30, 2023 at 12:15
  • $\begingroup$ maybe they were not tested at higher altitudes ... try asking the manufacturer $\endgroup$
    – jsotola
    Jun 30, 2023 at 15:21

4 Answers 4

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Electronic components are rated for altitude because:

  1. Air density affects convective cooling, both forced and natural, meaning the cooling is reduced at altitude.
  2. Air density affects air's dielectric properties and susceptibility to arcing (Paschen's Law). This means that air gaps and surface paths need to be designed differently for high-altitude use.

I'm guessing the EE SE would crush this one out of the park with real-world examples.

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  • $\begingroup$ Air pressure affects airs insulation properties. The effect on dielectric property affects it's capacitance, but not it's susceptibility to arcing. $\endgroup$
    – david
    Aug 14, 2023 at 22:23
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Expanding item 2 in Tiger Guy's good answer I'd say it's definitely about dielectric strength.

Electronic devices manufacturing standards (e.g. IEC62368-1) define creepage and clearance distances according to nominal voltage, basic or reinforced isolation need, materials and categories, aka environment where the device is supposed to be used.

The required distances are finally up-scaled according to maximum allowed altitude.

Infact Paschen's law relates dielectric withstand with atmospheric pressure.

So good manufacturers specify the choices done when designing.

https://www.powerctc.com/en/node/4757

https://en.wikipedia.org/wiki/Paschen%27s_law

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  • $\begingroup$ Thanks for the additional links, they are helpful! $\endgroup$ Jul 3, 2023 at 11:41
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One possible factor is that convection cooling of the components becomes less effective at high altitudes. Thinner air doesn't carry heat away as well.

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  • $\begingroup$ At least it's one possible explanation, however my meter does not get hot. This would more likely be an issue with a solar inverter or so, but the meter is usually cool. $\endgroup$ Jun 30, 2023 at 12:18
  • $\begingroup$ Just because the outside of your meter does not get noticably hot does not mean that parts of the inside of your meter do not get hot. When heat is an issue in electronics design, there is usually one or two hot spots that you need to worry about; not the whole assembly. $\endgroup$
    – TimWescott
    Aug 15, 2023 at 22:23
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Here's a good answer on electronics.stackexchange

Briefly: air is ionized by being hit by fast electrons. When there is less air, the electrons move farther between collisions, and become faster and more energetic before hitting an air molecule.

This also creates the counter-intuitive effect that it requires more voltage to get an arc as items get very close: if the electrons don't have enough space to accelerate, they don't get enough energy to ionize air molecules.

At very high altitudes (the edge of space) there isn't any air at all, and arcing becomes less of a problem.

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