46 CFR §113.25-16

1. (a)Each fuse in a general emergency alarm system must meet the requirements of part 111, subpart 111.53, of this chapter.
2. (b)Each overcurrent protection device must cause as wide a differential as possible between the rating of the branch circuit overcurrent protection device and that of the feeder overcurrent protection device.
3. (c)The capacity of the feeder overcurrent device must be as near practicable to 200 percent of the load supplied. The capacity of a branch circuit overcurrent device must not be higher than 50 percent of the capacity of the feeder overcurrent device.