The Schneider Electric LA9FJ4J4H is a mechanical interlock from the TeSys F range, designed to physically prevent two contactors from closing at the same time. It's a safety-backbone piece for anyone building reversing or star-delta motor starters where simultaneous closure would short the line.
What It Interlocks
This interlock handles a specific stack-up: it mounts between three vertical contactors. The bottom position accepts LC1F265 through LC1F330 in 3- or 4-pole, or CR1F265 in 3-pole. The top and middle positions both take LC1F400 or CR1F400 in 2-, 3-, or 4-pole versions. That covers the heavy F-frame contactors up to 400 A frame size, so it's sized for the larger motor control centers.