The statement “the primary is insulated from the secondary” regarding auto transformers is?

In the context of autotransformers, the statement “the primary is insulated from the secondary” is false because autotransformers operate using a single winding that serves both as the primary and secondary. This design means that there is no electrical isolation between the input and output sides, which contrasts with traditional transformers that have separate primary and secondary windings typically insulated from each other.

The way an autotransformer works allows a portion of the winding to act as both input and output, creating a situation where the primary and secondary circuits are interconnected. This lack of isolation can be advantageous in certain applications, as it leads to a more compact design and higher efficiency but also means that the full range of safety provided by electrical isolation is not present. Therefore, understanding the operation principle of autotransformers clarifies why the original statement is incorrect.