Influence of Relative Humidity on Aging

@TW: used in Maintenance Guides: DOCA0305 (MTZ with Mic Act), DOCA0099 (MTZ with Mic X), LVPED508016 (NT/NW)

Influence	Appearance	Consequences
Corrosion of metal surfaces that is accelerated when a pollutant is present (for example, corrosive gas, salt, chlorine).	Appearance of: Red rust on iron White rust on zinc Blue deposit on copper Black deposit on silver	Increase in friction Potential risk of mechanical rupture resulting in non-operation of mechanisms Increase in contact resistance (clusters and main contacts)
Deterioration of dielectric qualities of plastics.	White traces on case	Potential risk of a reduction in insulation
Deterioration of electronic components, in particular SMCs and silver-coated components. This phenomenon is worsened by the presence of H₂S corrosive gas (hydrogen sulphide).	Not visible Appearance of dendrites on electronic boards	Short-circuiting of circuits resulting in non-operation of control unit protection, measurement, indication and communication functions
Deterioration of electronic components, in particular non-varnished copper circuits.	Not visible Erosion of copper tracks Oxidation of metal connectors of components and metal cases Oxidation of connectors of integrated-circuits mounted on supports	Potential failure due to short-circuit or open circuit on electronic components Rupture of component connectors along case Poor contact with integrated-circuit supports
Degradation of opto-electronic components.	–	Potential failure of data transmission

The maintenance and installation recommendations according to the relative humidity are defined in the following table:

Relative humidity	Description	Maintenance recommendations	Installation recommendations
≤ 70 %	Level of relative humidity generally found in continental and temperate zones. The level is generally lower in switchboards due to the internal temperature rise. No significant deterioration is noted at this level.	Preventive maintenance	No particular recommendation
70 % to 85 %	Level of relative humidity generally found in zones close to water. Possible appearance of condensation on cold parts and accelerated rusting.	Carry out more frequent periodic checks. Measurement of insulation resistance (dielectric strength) is advised every five years.	No particular recommendation
> 85 %	Level of relative humidity generally found in tropical zones and certain factories (for example, paper mills). Increased possibility of condensation and rust resulting in difficulties to disconnect devices, possibility of non-opening or non-closing.	Carry out more frequent periodic checks. Inspect for rust on metal parts. Measurement of insulation is imperative every two years.	Install heating resistors in the switchboard.