What it is and where it lives in the panel
The ABB 129A535G01 is a medium-voltage switchgear test switch — the dedicated front-panel device used to isolate, short, and access current-transformer and voltage-transformer secondary circuits during commissioning, relay testing, and periodic maintenance on MV switchgear cells. It sits in the ABB circuit breaker accessories family under the Circuit Breaker Busways & Switches sub-category, which means it is specified as a cabinet-mounted test accessory alongside the breaker cell rather than as a breaker itself.
Spec thinness and what that means for sourcing
Functional detail lives in the cell wiring diagram and the original switchgear documentation; order to the exact part number 129A535G01 rather than re-engineer from a parameter list.
Sourcing posture and RFQ path
For a critical spare on an installed MV lineup the right cadence is one in the cabinet before it fails: hold a confirmed 129A535G01 against the cell wiring so a failed test switch during a relay check does not idle the breaker.