Schneider Electric 9999R8 Disconnect Interlock Switch

Schneider Electric’s Square D 9999R8 Series-B NEMA electrical interlock kit for disconnect switches is a SPDT, single-pole interlock designed for use with disconnect-type assemblies. The 9999R8 interlock is part of the Square D 9999 family and is specified for 200 A disconnect-type equipment, Type S configuration. It provides interlocking action that disconnects the separate control voltage source when the main disconnect is operated to OFF, ensuring the control circuit cannot be energized while the main switch is in use or opened. This makes it well suited for industrial motor-control scenarios where safety interlocks are required between the main disconnect and control circuitry. Typical applications include combination starters or disconnect switches in 200 A motor-control installations, where an auxiliary control circuit must be de-energized as the main switch position changes. The Series-B design variant is intended to be compatible with the corresponding Square D disconnect components, supporting a reliable safety interlock arrangement in enclosures housing disconnect switches and associated control circuitry.