**Power**

The power is expressed in kW (1kW = 1.34 hp).
The powers listed on this page are based on maximum powers at a constant load, so that thermal balance is achieved; also called S1 tax. Other load types, such as short-term and intermittent (S2,S3,S4, etc.), can influence the maximum power that may be drawn from the electric motor, where in combination with the ambient temperature, the maximum allowable temperature limit of the insulation materials used is not exceeded. May be exceeded. With the right combination of electric motor type and application, the efficiency will be as high possible, and the smallest possible housing size can be chosen.

**Types**

The operating modes (S1 to S10), which are laid down in the publication IEC 60034-1, indicate the service life or frequency of use of an electric motor. The load limit to which an electric motor can go is generally determined by the maximum allowable temperature of the stator and/or rotor. The standard powers normally used re the so-called IEC recommended power based on S1 continuous operation of the electric motor.

**S1: Continuous operation**

Operate at constant load for such a time that thermal equilibrium is achieved. The power stated on the rating plate may be drawn continuously.
The type plate states: S1

**S2: Short-term operation**

Operation at constant load for a specified period shorter than that during which thermal equilibrium would be achieved, followed by a rest period of sufficient duration to allow the temperature difference between the machine and the coolant to return to less than 2K. The operating time of the electric motor is a maximum of the specified time, after which the electric motor cools down to ambient temperature. The rating plate states, for example: S2 – 5 min. (alternatively: 10, 20 or 30 min.).

**S3: Intermittent periodic operation**

Operation composed of a series of equal cycles, each consisting of a period of constant load and a rest period. In this operation the cycle is such that the starting current has no significant influence on the temperature increase. The electric motor is switched on/off, with the load duration corresponding to the stated percentage. The on/off period is normally set to 10 minutes. The rating plate states, for example: S3 – 15% (alt. 25, 40 or 60%).

**S4: Intermittent periodic operation with starting**

Operation composed of a series of equal cycles, each consisting of an important start-up period, a period of constant load and a rest period. Business type like S3, however, with the influence of the run-up. In this example the switch-on time is 25% (7.5 sec. of 1 cycle 0.5 min.=120 c/h + maximum inertia data). The type plate then states: S4 – 25% 120 + maximum inertia data.

**S5: Intermittent periodic operation with electric braking**

Operation composed of a series of equal cycles, each consisting of a start-up period, a constant load period and a rapid electric braking period and a rest period. Operating type as S4, however, with the influence of electric braking. The type plate states, for example: S5 – 25% and the maximum inertia data.

**S6: Continuous operation with periodic intermittent load**

Operation composed of a series of equal cycles, each consisting of a period of constant load and a period of no load. There is no rest period. The electric motor runs continuously, however, the load is equal to the power stated on the rating plate for, for example, 40% of the cycle (normally 10 minutes). The rating plate states, for example: S6 – 40%.

**S7: Continuous operation with periodic electric braking**

Operation composed of a series of equal cycles, each consisting of a start-up period, a constant load period and an electric braking period. There is no rest period. Operating type as S5, but without rest period. The type plate then states: S7 (+ cycle data etc.).

**S8: Continuous operation with periodically changing load and speed**

Operation composed of a series of equal cycles, each consisting of a period of constant load at a given speed, followed by one or more periods of other loads involving different speeds (e.g. caused by a change in pole number). There is no rest period. The type plate then states: S8 (+ cycle data etc.)

**S9: Operation with non-periodically changing load and speed**

Operation where, in general, the load and speed do not change periodically within the permitted operating range. During this operation, repeated overloads occur, which can be much greater than the reference load. For this operation, a conveniently chosen constant load, based on operating type S1, is taken as a reference value ('Pref') for the overload model. The rating plate states S9 – (+ cycle data etc.).

**S10: Operation with different constant loads**

Operation consisting of no more than four different load values (or equivalent loads), each maintained for a sufficient period of time to allow the engine to reach thermal equilibrium. The smallest load within a cycle may be zero (no load or rest). For this operating type, a conveniently chosen constant load, based on the operating type S1, must be taken as a reference value ('Pref') for the different loads. The type plate then states: S10 – (+ data cycle etc.).