Difference Between Full Load and Rated Conditions


Thread Starter


I am currently a degree student and I always confused between the terms of full load and rated conditions.

Can you guys explain in details regarding the difference between full load speed/current/voltage and rated speed/current/voltage? I am not sure whether they are the same. Besides, what is actually rated output power? I need a good example.

Bruce Durdle

For a pump driven by an electric motor, the rated voltage of the motor is the nominal value of the supply to which it is connected - eg 400 V. The rated current is related to the current-carrying capacity of the motor windings and in practice may be exceeded by a small amount for a short time - it actually depends on thermal effects. The power is similarly determined by the capability of the motor.

The pump will have a rating based on the maximum flow it can handle under specified conditions - this is a bit more fluid (sorry!) as it will depend on the fluid properties which are outside the scope of the pump supplier, eg vapour pressure and density.

The combination will be used in an application with nominal or design values for flow, pressure and temperature. Note that this value will be used for design purposes: once the plant is operational, a series of adjustments (de-bottlenecking) will be made to find the maximum capability of the whole system. Choice of pump and motor will be based on the nominal values for the flows etc, with a margin for possible increases in performance.

Full load values give the specified capabilities of the equipment: the rated values give the target operating levels in a given application. At 100 % flow (design target) the pump may be delivering 90 % of full flow, and the motor 80% of full power.
I am sorry for not specifying my question. I am asking regarding the rated and full load condition of dc motor...

Curt Wuollet

The same still applies. Rated is what the motor can sustain continuously. The way I interpret full load it would be very much the same for certain classes of motor/applications. But the terms can't be applied the same way for all DC motors. I like to use a car starter motor as an example. The continuous output rating would be far, far, less than what the motor is rated to do for 15 seconds in starter service. That gets into the definite purpose motors/ratings. Many DC motors are used at high ratings with a duty cycle stipulated for intermittent service like all sorts of actuators, winches, valve positioners,etc. The General Purpose motors are rated far more conservatively. And even the same motor can have different ratings depending on the application. And the ratings apply only at the rated load and other stated conditions. i have seen the same PM motor used as a 24V gear motor at a rated output and with a rectifier on the 120 line for a high RPM low load application. So there isn't really a fixed relationship between full load and rated. A better way to think of it is in terms of output over a range limited by heat, winding gauge, etc. The ratings are just a guide for a particular set of conditions.