The 1.5KE18A-E3/54: That 1500 W rating tells you the device can absorb a single transient up to that energy without failing — but the real clamp current is 59.5 A at 25.2 V, so the protection level is set by the clamp voltage, not the wattage alone.
Standoff, breakdown, and clamp — the protection window
Reverse standoff is 15.3 V — the rail voltage this diode sits across without conducting. Breakdown starts at 17.1 V minimum, and clamping maxes at 25.2 V when the full 59.5 A pulse flows. That 10 V window from standoff to clamp means a 12 V or 15 V rail gets clamped well before the downstream IC's abs-max rating, but a 24 V rail is already above the standoff and would leak. For a board that sees engine-bay heat or cold-soak, the 175°C max gives headroom.
Through-hole axial — board-fit and sourcing
DO-201AA / DO-27 axial package, through-hole mount. The 1.5KE footprint is standard across the series — same hole pattern as the 1.5KE6.8A through 1.5KE440A variants, so a single PCB layout covers the whole voltage range. Tape & Reel or Cut Tape packaging available.