For environments where the ambient temperature exceeds 40 degrees Celsius, the maximum continuous current rating of breakers, bussing and other current carrying components must be de-rated. 

The derating factor is determined by calculating the square root of [(105 - special ambient temperature)/65].  As an example, the maximum continuous current rating of a 4000 amp WL low voltage switchgear unit is operated in a 50 degree Celsius environment would be 3680 amps (4000 X .92). The .92 derating factor is calculated by taking the square root of 55 divided by 65.