What the 1500W rating means for your rail
The 1.5SMBJ17A: That 1500W figure is the peak dissipation the device can handle in a single surge event—it governs how much energy the diode can clamp before failing. For a 17V rail, the 27.6V clamping voltage at 54.4A means the downstream circuitry sees a maximum of 27.6V during the surge; anything above that and the diode is in breakdown, shunting the current to ground. The reverse standoff voltage is 17V, so this part sits on a 12V or 15V rail without conducting in normal operation. The breakdown begins at 18.9V minimum, giving a small window before the clamp kicks in. That 1.9V margin between standoff and breakdown is typical for Zener TVS diodes and prevents nuisance triggering from normal ripple.
Automotive-grade protection
For a 12V automotive bus, the 17V standoff leaves headroom above the nominal 12V but still clamps before the 36V load-dump threshold many ECUs specify.
The DO-214AA (SMB) package is a standard surface-mount footprint for TVS diodes in this power class. Tape & Reel packaging suits automated pick-and-place; the reel quantity is typical for production runs.