USCG Exam PracticeElectrical basics — generators, motors, and safety
A motor designed for a 40 °C ambient temperature must be used in a machinery space where the ambient temperature reaches 50 °C. Under 46 CFR §183.320, which action is required?
- A. The motor must be replaced with one rated for 50 °C before it can be used
- ✓ The motor may be used if derated to 80 percent of its full load rating, with overcurrent devices reduced accordinglyCorrect
- C. The motor may be used at full load rating provided additional ventilation is supplied
- D. The motor may be used at full load rating if the overcurrent device is increased to 125 percent
Why B is correct
46 CFR §183.320(b)(2) permits a motor designed for 40 °C to be used in a 50 °C ambient location, but only if it is derated to 80 percent of its full load rating and the rating or setting of the overcurrent devices is reduced accordingly. Operating at full load or simply adding ventilation does not satisfy the regulatory requirement.
Cited:46 CFR §183.320