What shows up on the BOM line
The ABB ACS550-U1-044A-4 is an AC drive in the ACS550-U1 family, sitting in the motor drives class alongside the rest of the U1 frame. The order code ACS550-U1-044A-4 is what gets typed into the BOM, and the chassis lands on the dock at 21.32 kgs. Catalog placement is Motors & Motor Controls › Drives › Motor Drives, which matches where panel builders and mill electricians expect to find a general-purpose industrial drive of this size.
Sparing against a same-frame sibling
Optioned same-frame units ACS550-U1-072A-4+B055+L512 at 34.02 kgs and ACS550-U1-059A-4+B055 at 36.29 kgs run heavier than the 21.32 kgs base; when +B055 or +L512 are on the BOM, match the optioned MPN on the PO, not the bare 044A-4.