In accordance with 46 CFR, Subchapter J (Electrical Engineering), each diesel engine driven generator prime mover must have an over speed device, independent of the normal operating governor. If in testing the over speed device, what should be the trip point setting in terms of rated speed?
• 46 CFR Subchapter J — Electrical Engineering requirements for generator prime movers • Purpose of an overspeed device versus a normal speed governor • How Coast Guard rules typically set maximum allowable percentage above rated speed for safety-critical trips
• Look up the specific 46 CFR Subchapter J section that addresses diesel engine driven generator overspeed devices and note the exact percentage stated there. • Consider why the overspeed trip point must be independent of the governor and what that implies about how conservative (low) the trip setting should be. • Compare the options: which percentage seems too high to adequately protect against mechanical damage at overspeed, and which seems more consistent with a strict safety margin?
• Verify in current 46 CFR Subchapter J the exact language for "each diesel engine driven generator prime mover must have an overspeed device" and note the specified maximum percent above rated speed. • Confirm that the regulation uses a "not to exceed" limit, not a range, so you are looking for a single maximum value. • Double-check that the percentage is expressed relative to rated speed of the prime mover (not rated power, frequency, or voltage).
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