What lands on the BOM line
The ACS550-U1-012A-4+B055+L512: Mass on the listing is 7.26 kgs, which puts the unit in the bracket a single technician can lift onto a DIN-backplate or wall-mount bracket without rigging — worth knowing for the line-down spare because it decides whether the unit walks out to the panel in hand or on a cart.
Sourcing posture and what to ask for
The brand is ABB, and the configured string ACS550-U1-012A-4+B055+L512 is what gets typed into the purchase order — quoting against the bare frame number drops the +B055 and +L512 options and yields a different unit, so the suffixes travel with the line item.