What the 1.5SMCJ14A is and why it protects
The 1.5SMCJ14A_R1_00001: It clamps transients on a single power line — no power-line protection flag, so it is not a mains-suppressor, but it handles the 10/1000µs surge waveform common in board-level protection designs.
Standoff, breakdown, and clamping — the three voltages
The reverse standoff voltage is 14V typ, meaning the device sits idle below that level and conducts nothing in normal operation. The minimum breakdown voltage is 15.6V — the point where it starts to avalanche.