Effect of lower humidity on indoor Electrical Equipments 2

[krisys]

What is the effect of lower humidity (i.e; say much lower than 50% relative humidity)on the performance of indoor Electrical Equipments like switchgears, panels UPS etc.

As I understand, for the electrical equipments humidity variation by a wide range is considered to be more risky, as it would result in condensation. However, having relatively lower humidity should be a favourable scenario.

Any view?

 

[jraef]

You generally don't see a lower limit on relative humidity for simple things like swithchgear, but many electronic components will have a lower limit of 5% because of the increased risk of static. The thing is, electronics have invaded nearly every corner of the electrical equipment world, so it's a safe bet to stick to 5% as a lower limit of RH.


"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington

 

[krisys]

jraef,
Thank you very much. Quite convincing reply.

 

[KuanYau]

To krisys (Electrical)(OP)

In the IEC world, for "Low-voltage switchgear and controlgear assemblies" was previously covered by IEC Standard 60439-., now replaced by new IEC 61439-.
The IEC 61439-1 defines the general requirements for all the following product sections in the 61439-. series.

In the IEC 60439-1
a) Clause 6 [Service conditions]; where sub-clause 6.1 [Normal service conditions] states "ASSEMBLIES conforming to this standards are intended for use under the following service conditions" with Note "If components, for example relays, electronic equipment, are used which are not designed for these conditions, appropriate steps should be taken..."
b) Sub-clause 6.1.2.1 [Atmospheric conditions for indoor installations] "The air is clean and its relative humidity (RH*)does not exceed 50 % at a maximum temperature of +40 degree C. Higher relative humidities may be permitted at a lower temperatures, for example 90 % at +20 degree C. Care should be taken of moderate condensation which may occasionally occur due to variation in temperature"
c) Sub-clause 6.1.2.2 [ Atmospheric condition for outdoor installations]....
There is no guideline on the effect with (RH*)much lower than 50 %.

In general, (RH*)is not a major issue in LV systems and components voltage, current, making/breaking capacity ratings and clearance/creepage distance requirements.
The Standard does not stipulate the (RH*) value for insulation/impulse tests(for voltage rating),temperature-rise test(for current rating), voltage+current+power-factor(for making/breaking capacity tests)and separation distance (for creepage and clearance distance requirements).
Likewise, test laboratories do not adjust, record or report on the (RH*) value during the above tests/measurements.

 

[prc]

Willl we ever come across a RH of the order of 5 % in real world.My understanding is that even humans cannot stand such RH for long.

 

[davidbeach]

At low temperatures, a very low RH is easily achievable. Great effort and expense can be expended to get the RH up to something tolerable for humans, along with raising the temperature. Equipment installed outdoors under such conditions could be subject to those very low RH levels.

 

[77JQX]

I just checked the average humidity for where I live. The site "weatherspark.com" says "The relative humidity typically ranges from 14% (very dry) to 89% (very humid) over the course of the year, rarely dropping below 8% (very dry) and reaching as high as 100% (very humid). The air is driest around August 3, at which time the relative humidity drops below 17% (dry) three days out of four; it is most humid around December 27, exceeding 85% (humid) three days out of four."

If you're selling to my area, you better make sure your equipment will withstand 'on the order of' 5% RH.

 

[jraef]

But as I said, the only place I see a lower limit to RH is in electronics, and it is generally 5%, which is, let's just say, very uncomfortable for humans. I have to travel to Las Vegas and Phoenix quite a bit, and the RH in those areas is frequently in the teens; I was in PHX last week and it was 17%, very uncomfortable for me.

There was a week or so back in 2011 where the RH in Las Vegas dropped below 5% several times, hitting the record low for the US at 1%. There were a LOT of electronic board failures that week.


"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington

 

[cswilson]

Wouldn't the real issue here be specific (absolute) humidity? Relative humidity is expressed as a percentage of the saturation vapor pressure for a given temperature. But the SVP increases rapidly with temperature.

If I read the charts right the SVP at 40C is more than 10 times higher than that at 0C. So 50% RH at 0C would have less water vapor concentration than 5% RH at 40C.

I am presuming that it is the absolute concentration of water vapor in air that controls its electrical conductivity and its ability to bleed off charges that would determine the risk of harmful static electric discharges.

 

[Compositepro]

In most cases it is the relative humidity that controls how materials behave. For example, at 100% relative humidity, the air is saturated with moisture and exposed materials will be saturated with moisture. As relative humidity decreases the amount of moisture in the air decreases as well as the amount of moisture in exposed materials.