What the 1500 W peak pulse rating means for your rail
The 1.5SMC15A-E3/57T: That 1500 W rating means it can clamp a 70.8 A surge pulse down to 21.2 V, protecting a 12.8 V nominal rail from transients like inductive kickback or lightning-coupled spikes. The breakdown voltage range starts at 14.3 V minimum, so the device triggers before the rail sees damaging overvoltage, and the 12.8 V reverse standoff gives margin for a 12 V bus with normal ripple.
Housed in the DO-214AB (SMC) package, also referred to as SMCJ, this is a standard surface-mount footprint for medium-power TVS diodes. The package is rated for -65°C to 150°C junction temperature, covering industrial and automotive under-hood thermal profiles without derating.