If a DC motor designed for 45°C ambient temperature is to be used for 55°C ambient temperature, then the motor ___________(a) Of lower HP should be selected(b) Of higher HP should be selected(c) Can be used for 50°C ambient temperature also(d) Is to be de-rated by a factor recommended by manufacturer and select the next higher H.P. motorThe question was asked in an interview for internship.My question is from DC Motor Basics -2 in division DC Motors of DC Machines

If a DC motor designed for 45°C ambient temperature is to be used for

1.	If a DC motor designed for 45°C ambient temperature is to be used for 55°C ambient temperature, then the motor ___________(a) Of lower HP should be selected(b) Of higher HP should be selected(c) Can be used for 50°C ambient temperature also(d) Is to be de-rated by a factor recommended by manufacturer and select the next higher H.P. motorThe question was asked in an interview for internship.My question is from DC Motor Basics -2 in division DC Motors of DC Machines
Answer» Right choice is (d) Is to be de-rated by a factor recommended by manufacturer and SELECT the next higher H.P. motor The EXPLANATION: The ambient temperature is one of a factor in derating.If the ambient temperature given is HIGH, the insulation may REACH its maximum temperature LIMIT quickly.Hence, the motor may have to be de-rated, and for application next motor must be used.

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