TL;DR

Study overcurrent protection device selection, sizing, and coordination. Proper overcurrent protection prevents fires and equipment damage and is a critical exam topic.

By Valenke Exam Prep Team·Last updated 2026-06-03

Free Fuse & Breaker Sizing Practice Questions

Journeyman Electrician License Exam · Overcurrent Protection

This module covers Fuse & Breaker Sizing as part of the Overcurrent Protection section, testing your understanding of core concepts and their practical application.

Exam	Journeyman Electrician License Exam
Pass Rate	55%
Duration	240 minutes
Module	Fuse & Breaker Sizing

Why Fuse & Breaker Sizing matters

Fuse & Breaker Sizing is heavily tested because undersized conductors and services cause overheating, fires, and equipment failure.

Sample Practice Questions (5)

1. Per NEC 240.4, conductors shall be protected against overcurrent in accordance with their ampacities. What is the primary purpose of an overcurrent protective device (OCPD)?

To open the circuit before the current reaches a value that will cause damage to conductors or equipment
To increase the available current to connected loads
To regulate voltage supplied to the circuit
To provide a grounding path for fault currents

2. Per NEC 240.4(B), the next standard overcurrent device rating above the conductor ampacity is permitted for conductors of what size or larger?

14 AWG and larger
10 AWG and larger
1 AWG and larger
All conductor sizes

3. A 3 AWG THHN copper conductor has an ampacity of 115A per Table 310.16 (75°C column). Using the next standard size up rule per NEC 240.4(B), what is the maximum OCPD rating for a non-motor, non-multioutlet receptacle circuit?

110A
125A
100A
150A

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4. What is the primary difference between a dual-element (time-delay) fuse and a single-element fuse?

Dual-element fuses have higher voltage ratings
Dual-element fuses can handle temporary overloads and motor inrush currents without blowing
Single-element fuses are more expensive
Dual-element fuses only protect against short circuits

5. A circuit has conductors with an ampacity of 28 amperes. Per NEC 240.4(B), what is the maximum standard overcurrent device rating permitted using the next-size-up rule?

30 amperes
25 amperes
35 amperes
40 amperes

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Frequently Asked Questions

How many Fuse & Breaker Sizing questions are on the Journeyman Electrician License Exam?▼

The Overcurrent Protection section, which includes Fuse & Breaker Sizing, typically represents a significant portion of the exam. Focus on understanding core concepts rather than memorizing exact question counts, as the exam uses adaptive testing.

What is the best way to study Fuse & Breaker Sizing?▼

Practice solving calculation problems daily rather than just reading formulas. Work through problems step-by-step, check your units, and time yourself to build speed and accuracy under exam conditions.

What topics within Fuse & Breaker Sizing should I focus on most?▼

Focus on the concepts that appear in our practice questions and any areas where you consistently score below 70%. The adaptive practice mode will automatically target your weak areas for efficient study.