Cyndi Nyberg 
Former EASA Technical Support Specialist 

NEMA MG-1-12.45 states that motors shall operate successfully under running conditions at rated load with a variation in the voltage or the frequency up to the following: 

• Plus or minus 10 percent of rated voltage, with rated frequency. 
• Plus or minus 5 percent of rated frequency, with rated voltage. 
• A combined variation in voltage and frequency of 10 percent (sum of total values) of the rated values, provided the frequency variation does not exceed plus or minus 5 percent of rated frequency. 

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