The 1.5SMBJ48CA: That 1500 W rating means it can clamp a 19.4 A surge (the peak pulse current at that waveform) without the junction exceeding its temperature limit — the energy is absorbed and dissipated as heat through the DO-214AA package.
Protection window: 48 V standoff, 77.4 V clamp
The reverse standoff voltage is 48 V — the line voltage it sits across without conducting. Breakdown starts at 53.3 V minimum, and the clamping voltage peaks at 77.4 V at the rated surge current. That 24 V spread between standoff and clamp defines the protection margin: the downstream circuitry must survive the clamped voltage during the surge event. No need for two unidirectional diodes in anti-series. Operating junction temperature range spans -55°C to 150°C, so it holds its breakdown voltage and leakage specs across industrial and under-hood automotive environments without derating the peak pulse power.
Package and field-swap note
The body is large enough to hand-solder with a fine-tip iron if you are replacing one on a board without a hot-air station — just pre-tin one pad, align, reflow, then solder the second. The cathode band is absent on a bidirectional part, so orientation does not matter; it goes either way.
The 1.5SMBJ series is a standard catalog product, so supply continuity is typical for a mainstream TVS diode in this package and power class.