USCG Exam PracticeElectrical basics — generators, motors, and safety
A motor designed for a 40 °C ambient temperature must be operated in a space where the ambient temperature reaches 50 °C. Under 46 CFR §183.320, what is required?
- A. The motor must be replaced with one rated for 50 °C; no derating is permitted
- ✓ The motor may be used if derated to 80 percent of full load rating, with overcurrent devices reduced accordinglyCorrect
- C. The motor may be used at full load provided additional ventilation is supplied to the space
- D. The motor may be used at full load if the overcurrent device is increased to 125 percent to allow for heat-related current rise
Why B is correct
46 CFR §183.320(b)(2) permits a 40 °C-rated generator or motor to be used in a 50 °C ambient location, provided it is derated to 80 percent of its full load rating and the rating or setting of the overcurrent devices is reduced accordingly. Simply adding ventilation or increasing overcurrent protection is not an authorized alternative under this section.
Cited:46 CFR §183.320