What 292 V clamping means for the protected rail
The 1.5SMCJ180AS_R1_00001: The standoff rating of 180 V defines the working voltage the TVS sees in normal operation — the part stays off the characteristic until the transient pushes it into avalanche at the 198 V minimum breakdown point. When the surge arrives, the 292 V clamping ceiling at 5.1 A peak pulse (10/1000 µs) is the number that limits the voltage impressed on whatever is behind it — the downstream circuit sees 292 V, not the raw transient, which is the whole point of fitting a TVS at the entry point.