What the 1500W peak pulse rating means for your rail protection
That 1500W rating is the energy-handling ceiling for a single pulse — beyond it the junction overheats and the protection collapses. For a 15.2V rail, the 54.2A peak pulse current tells you the diode can sink a direct lightning surge or inductive kick without failing short.
Voltage window: standoff, breakdown, and clamping
Reverse standoff is 15.2V — the rail voltage the diode leaves alone during normal operation. Breakdown starts at 19V minimum, and clamping is 27.7V maximum at the rated pulse current. That 8.5V gap between standoff and clamping is the voltage the downstream circuitry must survive; if your load's absolute maximum is 26V, this part clamps too high and you need a lower-voltage device.
Temperature range and package — built for harsh environments
The SQ-MELF C package is a hermetic surface-mount ceramic body; it resists moisture and thermal cycling better than plastic SMD packages, which matters for long-life mission equipment.
The base product number is 1N6149, so the same die is available in other package variants if the SQ-MELF footprint is not a fit.