An electric motor needs to be able to perform its main function continuously, although it may not meet its performance specifications at rated voltage and frequency and may suffer some deviations. The temperature increases may be higher according to nominal voltage and frequency. An engine must be able to perform its main functions, and may present larger deviations, in terms of performance specifications at rated voltage and frequency.
Temperature increases may be higher than those at rated voltage and frequency, so prolonged operation is not recommended. The starting of a three-phase cage motor must be direct, via contactors. It must be considered that for a given motor, the torque and current curves need to be fixed, regardless of the load, for a constant voltage.
If the motor starting current is high, some damaging consequences can occur, such as the high voltage drop in the mains supply system. Due to this factor, interference may be caused to equipment installed in the system. The protection system of cables and contactors will need to be oversized, generating a high cost.