Which of the following is considered an uncommon fuse size?

The answer identifies 75 ampere fuses as the uncommon size because it is less frequently found in standard residential and commercial applications compared to the others listed. Most commonly used ampere sizes tend to follow standard increments for residential services, such as 60, 90, and 100 ampere fuses, which are typical for circuit protection.

The 60 amp fuse is often used for smaller circuits, and 100 amp fuses are standard for main service panels in many homes. The 90 amp fuse can be found in applications where slightly higher capacity is required, often in larger residential circuits or specific equipment. The 75 amp fuse does have its applications, but it is not as widely adopted or recognized as a common standard size, making it uncommon. This context helps clarify why 75 amp is viewed as less typical than the others listed.