What it is on the BOM line
The ABB ACS355-03U-05A6-4+J400 is the 2.2 kW class entry in the ACS355 micro-drive family, framed for 400 V three-phase operation, and the +J400 suffix in the order string is the option code the BOM has to carry verbatim when the panel-builder is matching an existing schematic or spare list. At 1.04 kg the drive is in the wall-mount / IP20 panel-mount weight class the ACS355 line is known for — light enough to land on a standard DIN-rail backplate inside a small control cabinet, heavy enough that a single technician handles the swap-out without a second pair of hands. Buyers who need the ABB ACS355-03U-05A6-4+J400 datasheet, wiring diagram, or error-code reference should match the order string character-for-character; the +J400 option suffix is part of the configuration key and a bare ACS355-03U-05A6-4 will not be the same factory build.
Where this class is used
ACS355-class drives are the workhorse choice for OEM machines that need sensorless vector control on fractional-to-low-kW induction or permanent-magnet motors — conveyors, mixers, small pumps, fans, packaging-line feeders, and the auxiliary axes around a packaging cell. The +J400 option code on an ACS355 is typically the configuration the OEM uses to fix a specific keypad, I/O, or fieldbus option set at the factory; the installer relies on that option being honoured because the wiring print and parameter file are written against it, not against a generic 05A6-4 frame.
Same function, different platform — ACS380 sibling
The ACS380-040C-05A6-4+K475 is the peer MPN on record at 1.13 kg, and it is the natural cross-shop candidate when a buyer weighs newer-platform supply against an existing ACS355-03U-05A6-4+J400 spec line.
Sourcing posture
The ACS355-03U-05A6-4+J400 is specified to the BOM and quoted to order against an RFQ; obsolete-line rebuilds and parallel-import builds route through the same RFQ channel, with the ACS380-040C-05A6-4+K475 available alongside it.