New York State Master Electrician Practice Exam

Under what condition are fuses and circuit breakers permitted to be connected in parallel?

1. When they are of different ratings

2. When they are factory assembled in parallel and listed as a unit

3. When using a common disconnect

4. When installed in the same enclosure

The correct answer is: When they are factory assembled in parallel and listed as a unit

Fuses and circuit breakers can be connected in parallel when they are factory assembled in parallel and have been listed as a unit. This condition ensures that the devices are tested together, confirming that they will operate reliably in a parallel configuration and provide protection as intended. The reason for this specification is rooted in safety and performance standards. When devices are designed and tested together as a single unit, they can account for the specific interactions and current distribution that may occur when connected in parallel. This compliance with strict testing protocols helps ensure that both devices function correctly without interfering with each other's operation. In contrast, connections involving different ratings, common disconnects, or simply being installed in the same enclosure do not guarantee that the devices will function safely or effectively together. Each of these situations may lead to issues such as overloads, improper tripping, or failure to break the circuit under fault conditions, which can pose significant safety risks. Thus, the manufacturing and listing as a cohesive unit is crucial for their parallel operation.