What indicates a blown internal fuse in a transformer when testing it?

A blown internal fuse in a transformer is indicated by an "open" circuit. Fuses are designed to break the circuit when a certain threshold of current is exceeded, effectively preventing further electrical flow. When testing a transformer, if the circuit shows an open reading, it signifies that the fuse has blown and interrupted the flow of electricity, indicating that the transformer is not functioning properly.

In contrast, a short circuit would show continuity but could indicate a fault within the transformer rather than a blown fuse. A normal reading suggests that the transformer is intact and functioning properly, while low resistance might indicate a fault condition, but it does not specifically point to a blown fuse. Thus, identifying an open circuit is the direct confirmation of a blown internal fuse within the transformer.