How do you select a transformer to operate in an ambient higher than 40 degrees centigrade?

When the ambient exceeds 40 deg. C use the following chart for de-rating standard transformers.

Maximum Ambient Temperature Maximum Percentage of Loading

40 deg. C (104 deg. F ) 100%

50 deg. C (122 deg. F) 92%

60 deg. C (140 deg. F) 84%

Instead of ordering custom built transformers to operate in ambients higher than 40 deg. C, it is more economical to use a standard transformer of a larger KVA rating.

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