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Clause 9’s Table 38 for Touch Temperature Limits states the limits are based on a 25 deg C ambient. How are the Tmax limits in Table 38 adjusted for different ambient temperatures?

Clause 9’s Table 38 for Touch Temperature Limits states the limits are based on a 25 deg. C ambient and to adjust for different ambient temperatures if not 25 deg. C.  What if our product has a max. ambient temperature (Tma) rating of 40 deg. C? How are the Tmax limits in Table 38 adjusted?  Do we simply add 15 deg. C to the stated limit in Table 38?

There is a fundamental understanding of Clause 9 (Thermal Burn Injury) and Table 38 in the question.  The intent of 9.2.5, and additional explanation in IEC TR 62368-2, is to convey that the measurements per Clause 9 are made at 25 C ambient (with allowance for test environment), but they do NOT consider Tma, or the manufacturer’s specified ambient.  This is different than 60950-1, and thus also supports why the limits in Table38 are lower. However, the key rationale for why 25C based measurements are in 62368-1 is that the limits are based on IEC Guide 117, Electrotechnical equipment - Temperatures of touchable hot surfaces,and its reference standards, which includes research only conducted in 25 C ambients.

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