What the order code covers
The ABB 129A542G01 is a test switch in the PLC Expansion Modules line, slotted into a controls panel to provide a make-before-break test point on metering or protection circuits. It sits in the ABB PLCs & HMIs / PLCs and Accessories / PLC Expansion Modules tree, so the part is treated as a panel-side module rather than a standalone instrument — it is specified into a switchgear or relay cubicle and lands next to the protection relay or meter it serves.
Where it earns its place on a panel
This test switch is wired in series with the current transformer secondary and the meter or protection relay input, giving the field tech a safe way to short the CT and isolate the device under test without opening the secondary circuit.
Sourcing and RFQ posture
Sourcing for the ABB 129A542G01 runs as a specified-to-order line against an RFQ: the order code is the contract, and supply is quoted per the BOM line rather than off shelf. For sites already standardized on ABB FT-series test switches, this is the part to keep on the MRO shelf so a failed switch can be swapped without rewriting the CT wiring or disturbing the relay settings downstream.