Schneider Electric 9999-MM4 Mechanical Interlock Kit

The Schneider Electric Square D 9999-MM4 Mechanical Interlock Kit is a dedicated accessory that ensures only one of two connected contactors can be energized at a time, preventing backfeed and unsafe simultaneous operation. Catalog number 9999-MM4 (also listed as 9999MM4) is part of Square D's 9999 class of mechanical interlock kits designed to work with compatible contactors and starters from the Square D lineup. Verified usage notes indicate this kit functions as a mechanical interlock assembly to coordinate two devices in a dual-contactor installation, a common arrangement for transfer or interlock applications in electrical switchgear. According to distributor records, this specific interlock kit has been discontinued by Schneider Electric, so availability varies and warranties or factory support may be limited.