When must a transformer be derated?

A transformer must be derated when the ambient temperature exceeds 104ºF because elevated temperatures can lead to reduced efficiency and potential overheating of the transformer. Each transformer has a specific temperature rating, which indicates the maximum temperature it can handle while operating safely. When the ambient temperature exceeds this threshold, the cooling mechanisms may become less effective, leading to a higher risk of damage or premature failure. Therefore, derating the transformer ensures that it operates within a safer range, taking into account the increased thermal stress from the higher ambient conditions. This practice helps maintain reliability and longevity in the transformer's operation.

While capacity and location can influence transformer performance and selection, they do not specifically necessitate derating in the same way that excessive ambient temperature does.