Influence of Load on Aging

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

Percent Load (I/In)

The percent load affects the device temperature, which is itself affected by the ambient temperature.

Influence	Appearance	Consequences
Aging of plastic insulation	Change in color of insulation	Breaking of parts leading to potential failure of functions.
Aging of grease	Change in color and viscosity	Increase in mechanical friction.
Aging of electronic components	Modified display of LCDs	A 10 °C (50 °F) increase (that is, an 85 % load) reduces the service life of components by approximately half.
Deterioration of characteristics: of steel springs when temperature > 100 °C (212 °F) of stainless steel springs when temperature > 200 °C (392 °F)	Rupture	Non-operation of mechanisms.

Recommendations

The maintenance and installation recommendations according to the value of percent load (I/In) are defined in the following table:

Percent load	Description	Maintenance recommendations	Installation recommendations
I/In ≤ 80 %, 24/24 h	Maximum percent load taken into account in sizing the installation. At this percent load, temperature rise is reduced approximately 40 % with respect to a 100 % load.	Implement the Intermediate program.	Normal conditions
I/In ≤ 90 %, 8/24 h	At this percent load, temperature rise is reduced only 20 %. Heating and cooling cycles impact on the mechanical junctions of the power circuit.	Carry out more frequent periodic checks.	Normal conditions
I/In ≤90 %, 24/24 h	The thermal stress for continuous operation is three times higher than in the previous case, but the absence of thermal cycles slows aging of the electromechanical components.	Preventive maintenance is difficult due to the continuous process	Normal conditions
I/In = 100 %, 8/24 h	Between 90 % and 100 %, temperature rise is close to its maximum value. Heating and cooling cycles impact on the mechanical junctions of the power circuit, with major impact on aging.	Carry out more frequent periodic checks. Inspect for condensation.	Provide ventilation for the switchboard. Install a device with a higher rating.
I/In = 100 %, 24/24 h	Between 90 % and 100 %, temperature rise is close to its maximum value. This situation has a major impact on aging. It is not recommended.	Preventive maintenance is difficult due to the continuous process. Plan more frequent periodic checks.	Spread the load over other outgoers. Install a device with a higher rating.