Duty types S1 to S10 (IEC 60034-1)
A motor's rated power or torque only holds for the load pattern it was rated for. IEC 60034-1 names ten of these patterns, duty types S1 to S10. The motor heats up while loaded and cools while resting or idling, so the same motor can deliver more in a short or intermittent duty than in continuous running.
Duty types
| Type | Name | Load pattern | For sizing |
|---|---|---|---|
| S1 | Continuous running duty | Constant load, long enough for the motor to reach thermal equilibrium. | The plain rated power or torque. If your load never stops, size against this. |
| S2 | Short-time duty | Constant load for a set time, too short to reach equilibrium, then a rest until the motor is back at coolant temperature. | Written with the run time, e.g. S2 30 min. The motor can deliver more than its S1 rating, but only for that time. |
| S3 | Intermittent periodic duty | Identical cycles of constant load then rest. Starting does not noticeably heat the motor. | Written with the on-time share, e.g. S3 40 %. A higher load is allowed for a lower share. |
| S4 | Intermittent periodic duty with starting | As S3, but every cycle starts with a start that does heat the motor. | Besides the on-time share, the starts count: check start current and load inertia, not just the running load. |
| S5 | Intermittent periodic duty with electric braking | As S4, with electric braking at the end of each cycle. | Braking adds heat. Count it when estimating the RMS load. |
| S6 | Continuous operation periodic duty | Identical cycles of load then no-load running, without stopping. | Written with the share, e.g. S6 40 %. The motor keeps its fan running between loads, so it cools better than in S3. |
| S7 | Continuous operation periodic duty with electric braking | Cycles of start, load and electric braking, with no rest. | Typical of reversing drives. Heating from starts and braking dominates. |
| S8 | Continuous operation periodic duty with related load/speed changes | Cycles of load at one speed, then other loads at other speeds, with no rest. | Size per speed step; each step has its own load and share. |
| S9 | Duty with non-periodic load and speed variations | Load and speed vary without a repeating pattern, often with overloads well above the reference load. | The usual case for an inverter- or servo-driven axis. Size from the RMS torque of the real profile, then check the peaks. |
| S10 | Duty with discrete constant loads and speeds | A few fixed loads (and speeds), each held long enough to reach thermal equilibrium. | Rated with the expected thermal life relative to S1. |
Reading the datasheet
A rating without a duty type is normally the S1 rating; check the datasheet if in doubt. A percentage after S3 or S6 is the share of each cycle spent under load: S3 40 % means loaded for 40 % of the cycle, at rest for the other 60 %.
Servo motors are usually given with a continuous (S1) torque and a much higher peak torque. A servo axis runs a varying profile, so check two things: the RMS torque over the whole cycle stays below the continuous torque, and the highest torque in the cycle stays below the peak torque. The motion profile calculator gives the speeds and accelerations of a move to start from, and the drivetrain builder carries them through to the motor.
Summarised from the standard named above. For a design decision, check the motor maker's datasheet and the current edition of the standard. More datasheet reference pages.