According to 46 CFR, Subchapter J (Electrical Engineering), general emergency alarm system power supplies are required to have over current protection from a fused switch or circuit breaker. If the general emergency alarm system load when connected is 15 amps, what is the minimum required fuse rating if a fused switch is used for over current protection?
• 46 CFR Subchapter J requirements for overcurrent protection on emergency alarm circuits • Typical practice that protective devices for continuous loads are rated higher than the actual load current • Difference between fuse rating and load current (what each number is supposed to protect)
• If the alarm system draws 15 amps, would a fuse rated exactly 15 amps be likely to nuisance-blow during normal operation, or should it be sized with some margin? • Look at the answer choices: which ratings are only slightly above 15 amps and which are much higher than needed for proper protection? • Think about the purpose of overcurrent protection: it must protect the circuit, but still allow normal and slightly elevated starting/surge currents. Which option best balances those needs?
• Check whether 46 CFR Subchapter J calls for overcurrent devices to be sized not less than a certain percentage above the load, or simply "suitable" for the circuit. • Verify that the selected fuse rating is greater than 15 amps (so it won’t trip in normal service) but not excessively larger, which would weaken protection. • Confirm that the chosen value is a standard fuse size and represents a reasonable safety margin above 15 amps.
No comments yet
Be the first to share your thoughts!