Question

What is the major disadvantage of an auto transformer?

• A. High cost
• B. Low efficiency
• C. Lack of electrical isolation between primary and secondary
• D. Very heavy weight

Hint:

Auto transformers are smaller, cheaper, and efficient, but their main disadvantage is lack of electrical isolation.

Answer 1

The Correct Option is C

Concept: An auto transformer uses a single winding which is common to both primary and secondary circuits.

Step 1: In a two-winding transformer, primary and secondary windings are electrically isolated from each other.

Step 2: But in an auto transformer, a part of the winding is common to both sides.

Step 3: Because of this common winding, there is no complete electrical isolation between input and output.

Step 4: This can be dangerous in fault conditions because high voltage may be transferred to the low-voltage side. Therefore, the major disadvantage is: \[ \boxed{\text{Lack of electrical isolation between primary and secondary}} \]