The LA9FG4F4F is a TeSys F mechanical interlock — an accessory that physically prevents two or three contactors from closing simultaneously, which is essential in reversing or changeover motor starter circuits where a simultaneous close would create a phase-to-phase short.
Compatibility and Mounting
This interlock mounts in a 3-vertical configuration and is designed to interlock specific contactor pairs: bottom LC1F115...LC1F150 3P or 4P, bottom CR1F150 3P or 4P, middle LC1F115...LC1F150 3P or 4P, middle CR1F150 3P or 4P, top LC1F185...LC1F225 3P or 4P, and top CR1F185 3P or 4P.
The LA9FG4F4F is listed as obsolete. No official successor order code exists.
What the Interlock Does
Mechanical interlocking uses a physical bar or linkage between contactor armatures so that only one can be in the closed position at a time. This is a safety requirement per IEC 60947-4-1 for reversing starters — electrical interlocks alone can fail, so the mechanical interlock provides a redundant, fail-safe layer.