Updated: Dec 9, 2025 | Source: 2023-2027 Question Pool | Topic: G5C
G5C05G5C

Why is the primary winding wire of a voltage step-up transformer usually a larger size than that of the secondary winding?

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Deep Dive: G5C05

The correct answer is B: To accommodate the higher current of the primary. Why the primary winding wire of a voltage step-up transformer is usually larger than that of the secondary is to accommodate the higher current of the primary. In a step-up transformer, primary voltage is lower but current is higher, requiring larger wire. For amateur radio operators, this explains transformer wire sizing. Understanding this helps when designing transformers.

Why Other Answers Are Wrong

Option A: Incorrect. Larger wire doesn't improve coupling - coupling depends on core design and winding technique, not wire size. Coupling isn't the reason. Option C: Incorrect. Larger wire doesn't prevent parasitic oscillations - oscillations come from circuit design, not wire size. Oscillations aren't the reason. Option D: Incorrect. Wire volume equality isn't the reason - wire size is determined by current, not volume. Volume isn't the consideration.

Exam Tip

Step-up transformer primary wire larger = accommodate higher current. Think 'S'tep-up 'P'rimary = 'S'maller 'P'ower (voltage) but 'H'igher 'C'urrent. Primary has lower voltage but higher current, requiring larger wire. Not coupling, not oscillations, not volume - just current capacity.

Memory Aid

Step-up transformer primary wire larger = accommodate higher current. Think 'S'tep-up 'P'rimary = 'H'igher 'C'urrent. Primary has lower voltage but higher current, requiring larger wire. Wire size determined by current.

Real-World Example

A step-up transformer: 120V primary, 480V secondary (4:1 step-up). Primary current is 4× secondary current (power is same). The primary wire must be larger to handle the higher current, even though voltage is lower. Wire size is determined by current, not voltage.

Source & Coverage

Question Pool: 2023-2027 Question Pool

Subelement: G5C

Reference: 2023-2027 Question Pool · G5 - Electrical Principles

Key Concepts

Step-up transformer Primary winding Larger wire Higher current

Verified Content

Question from the official FCC General Class pool. Explanation reviewed by licensed amateur radio operators and mapped to the G5C topic.