What are the derating guidelines for low voltage switchgear installed in high ambient temperature environments?

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.