Question

In situations where a standard rating of a circuit breaker or fuse does NOT correspond to the permittable current rating of a 1,100 amp feeder busway, what's the largest standard rating of the overcurrent device?

1. 900 amperes
2. 1,000 amperes
3. 1,100 amperes
4. 1,200 amperes

Answer 1

The largest standard overcurrent device rating that corresponds to the permissible current rating of a 1,100 amp feeder busway, considering the 80% safety regulation, would be 1,000 amperes.

Step-by-step explanation:

When considering the largest standard rating of an overcurrent device that corresponds to the permissive current rating of a 1,100 amp feeder busway, note that circuit breakers and fuses are designed to protect electrical systems by interrupting the flow of excessive current. Safety regulations typically allow continuous use at only 80% of a breaker's or fuse's current capacity. Therefore, a device that is to be continuously used at 1,100 amps should have a rating higher than 1,375 amps (1,100 / 0.8), to adhere to the 80% rule. Keeping in mind the closest standard ratings, the largest standard overcurrent device rating you can use without exceeding the permissive current rating of the busway would be 1,000 amperes.