USCG Exam PracticeElectrical basics — generators, motors, and safety
A generator or motor designed for a 40 °C ambient temperature is installed in a space where the ambient temperature reaches 50 °C. Under what condition does the regulation permit this installation?
- A. Provided the machine is derated to 90 percent of full load rating and overcurrent devices are adjusted accordingly
- ✓ Provided the machine is derated to 80 percent of full load rating and overcurrent devices are adjusted accordinglyCorrect
- C. Provided additional ventilation is supplied to maintain the space below 45 °C
- D. Provided the machine is operated at no more than 50 percent load at all times
Why B is correct
46 CFR §183.320(b)(2) expressly permits a 40 °C-rated generator or motor to be used in a 50 °C ambient location only if it is derated to 80 percent of the full load rating and the rating or setting of the overcurrent devices is reduced accordingly. No other derating percentage or ventilation workaround is authorized by this section.
Cited:46 CFR §183.320