For machines with correct dimensioning, the resistant torque must be relatively smaller than the rated torque. https://www.mrosupply.com/couplings-collars/grid-couplings/478471_3701475_rexnord/ If it is similar or subtly higher, the resulting heating should be considered. In this way, an underloaded motor can present a considerable reduction in efficiency. The ideal loading needs to correspond to the workload to be carried out, a factor that is not always simple to determine. It should be considered that if the expected work of the driven machine exhibits any temporary overloads, the power of the motor should be slightly higher than the required power.
The increase in losses should be limited by periodically maintaining the necessary adequate maintenance of the machines as well as the mechanical drive components, such as clearance regulation, proper lubrication and checking of alignments. In a nutshell, it should be remembered that individual motors are more energy-efficient than multiple transmissions. In these cases a large decrease in the efficiency of a 4-pole three-phase asynchronous motor can occur due to the load presented in normal operating conditions. In the case of electrical losses, also known as thermal losses, they can be changed, depending on the square of the conjugate of the existing load.