Two SINAMICS G120X drives can wear the same frame and the same kW badge yet differ in the one number that trips them: the overload rating. The LO (light overload) variant is dimensioned for centrifugal pumps and fans — 110% of base load current for 60 s in a 300 s cycle, per the datasheet definition — while the HO (heavy overload) variant carries 150% for 60 s in a 600 s cycle. The HO (heavy overload) variant buys more headroom for loads that lean on the drive. Ordering an HO rating for a clean pump duty wastes money; ordering LO for a load that stalls its pump at closure head buys nuisance trips.
Read the load, not the nameplate
A centrifugal pump follows its curve: torque rises with the square of speed, and the worst case is start-against-static-head or a dead-headed discharge, not steady running. If your process can dead-head or choke the pump, size for that transient. Fans are gentler still — direct-coupled fan duty is the textbook LO case, while belt-driven units add bearing torque that deserves margin.
The order-code consequence
On the G120X the duty rating is part of the configuration: the same 250 kW pump room can be served by an LO-rated unit at one current rating or an HO-rated unit at a lower one for the same overload — the trade is printed on the datasheet as two current figures per frame. Catalog examples make it concrete: the 250 kW C3-filtered PROFINET pump drive is a pump-duty (LO) machine, while general-purpose variants like the 90 kW C2 full-feature drive show the heavier current reserve in their ratings.
If the load is truly mixed — a pump room that occasionally runs a hoist or compressor — step up the rating or step up the family. The broader drives and motors group covers the heavier-duty alternatives.
Is LO enough for soft-starting a big pump?
Yes, in the normal sense: a VFD ramps frequency, so start current stays near rated rather than the six-times DOL inrush. LO covers ramped starts; it does not cover a pump seizing against a closed valve at full speed.
Where do I find the LO/HO figures?
In the datasheet's rating table — two current columns per frame. Compare both against your motor's service-factor current and the worst transient in your process, then let that comparison pick the order code.
