New York State Master Electrician Practice Exam

Which type of cartridge fuses is permitted for replacement in existing installations without evidence of over-fusing?

1. Class G

2. Class F

3. Class H

4. Class J

The correct answer is: Class H

Class H cartridge fuses are specifically designed to be interchangeable within existing installations without the need for evidence of over-fusing. This is primarily due to their construction, which includes features that prevent overcurrent conditions. Class H fuses offer a standardized rating and are commonly used in residential and commercial applications, making them versatile and reliable for various electrical systems. These fuses are rated for branch circuits up to 600 volts and provide a means of protection while accommodating different current ratings. Their design allows them to effectively interrupt short circuits and overloads, adhering to safety regulations. In contrast, the other types of cartridge fuses may have specific applications or limitations that require careful evaluation before replacement. For instance, Class G fuses are generally used in low-voltage applications, Class F fuses may be involved in specialized circuits requiring different interrupting ratings, and Class J fuses may not be suitable for every existing existing installation without modifying the circuit. Thus, Class H fuses provide the broadest flexibility for replacements without the necessity of demonstrating that over-fusing has occurred.