What is true about transformer internal fuses?

• A. They are replaceable
• B. They are not replaceable; blowing the fuse destroys the transformer
• C. They can be reset after blowing
• D. They are external fuses only

Answer: (B)

Internal transformer fuses are one-shot protective devices built into the unit. They’re not designed to be field-replaced, and when they blow the transformer is effectively taken out of service because the winding has been protected from further damage. Resetting a blown fuse is unsafe, since it would bypass protection and risk further damage or fire. Although some installations use external fuses, that doesn’t change the fact that the internal fuse itself is not replaceable. So the accurate idea is that the fuse isn’t replaceable and a blown fuse typically means replacing the transformer rather than simply resetting or swapping a fuse.