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A service factor of 1.15 indicates that, at rated voltage and frequency, the motor is designed to withstand loading up to 1.15 times its nameplate power. On DRG crusher motors of 75 kW and above, this margin provides a safety band against the short load surges common in crushing plants, such as hard rock or uneven feed.
How much margin in numbers?
| Nameplate power | Upper limit with SF 1.15 | Example DRG model |
|---|---|---|
| 75 kW | 86.25 kW | DRG-280S-4-GG |
| 90 kW | 103.5 kW | DRG-280M-4-GG |
| 110 kW | 126.5 kW | DRG-315S-4-GG |
| 132 kW | 151.8 kW | DRG-315M-4-GG |
This margin keeps the motor from hitting its limit straight away at the moments when the crusher occasionally meets a hard block or a dense wave of feed.
What does the service factor not provide?
- It is not a margin added to power sizing: If the crusher needs 100 kW, choosing a 90 kW motor and saying “with SF it becomes 103 kW” is wrong. A motor running in this zone has a higher winding temperature and a shorter insulation life.
- It does not compensate for poor conditions: With low voltage, phase imbalance, a clogged fan cover or high ambient temperature, the margin may already be used up.
- It does not increase starting torque: The ability to accelerate a crusher with a heavy flywheel depends on the torque-speed curve; the SF value does not change it.
How is it used in operation?
Select the motor by its nameplate power and keep the margin for unexpected moments. If, in normal production, the current is regularly above the nameplate value, the problem lies not in the motor size but in the feed, the jaw or rotor setting, belt slip or the character of the material. Whether protection settings should take the service factor into account depends on the motor nameplate, the manufacturer's documentation and the assessment of qualified electrical personnel.
What to look at together when selecting
The power and speed recommended by the crusher manufacturer, the pulley ratio, the rotor or flywheel inertia and the starting method come before the service factor. Once these are clear, you can review suitable power steps on the stone crushing plant motors page and the dimensions in the product record of the 90 kW 280M cast iron model.