What this drive is
The ACS550-U1-031A-2+B055+L512 is an ABB ACS550-series wall-mount AC drive order code carrying the +B055 and +L512 option suffixes on the configured part string. On the buyer's side the headline is the order string itself: 031A fixes the current frame, the trailing -2 fixes the voltage class, and the +B055 +L512 suffixes are option codes that change I/O, feedback, or coating configuration depending on the option catalogue. The listed weight for this configured part is 3.86 kgs, which sets the panel-builder's bracket and cabinet-balance calculation.
Class context and option suffixes
The +B055 and +L512 suffixes are configured at order entry and are part of the order code, not field-installed accessories — when you source a replacement, both suffix strings must match the original BOM or the I/O, feedback, or environmental-coating configuration will not match the panel drawing.
Closest functional second-source — ACS580-01-031A-2
For a buyer asking whether the ACS580-01-031A-2 is a drop-in second-source: it is the closest functional alternative at the same 031A current code, but the ACS580 platform is a newer control generation with a different assistant-panel layout, parameter structure and firmware map. Same current frame, different drive family — it does not slot into an ACS550-commissioned panel without a parameter re-load and an I/O review. On the mechanical side the weight delta is panel-relevant: this ACS550 variant lists 3.86 kgs while the ACS580-01-031A-2 lists 2.99 kgs at the same 031A current code. That delta changes cabinet-balance and bracket-class decisions when retrofitters swap generations in the same enclosure cut-out.
Sourcing posture
For procurement, the order code is specified into the BOM as-is — the suffixes +B055 +L512 are part of the configured part number and must travel with the RFQ to ensure the option set matches the original panel design. Sourcing is run quoted-to-order against the configured code, not against a bare current rating. The ACS550 series has been a long-running ABB platform that the newer ACS580 family progressively supersedes, which is why the closest functional second-source on the buyer's shortlist is the ACS580-01-031A-2 at the same 031A current code. Where the original BOM calls for the ACS550 specifically — for parameter compatibility with existing commissioned drives on a shared line — the order code as written is the procurement target.