Red Seal Electrician Practice
TransformersQuestion 1143 of 1506

A dry-type transformer carries an insulation class letter A, B, F or H. What does the letter set?

  1. The turns ratio between the primary and secondary
  2. The number of taps that the winding may have
  3. The output frequency
  4. The maximum winding temperature rise above ambient
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Correct answer: The maximum winding temperature rise above ambient

The letters are arranged from the lowest heat tolerance (A) to the highest (H).

Source: Lessons in Electric Circuits II: AC (Kuphaldt), 10.8: Practical Considerations - Transformers

Practice transformers

Questions last reviewed: 18 October 2026