The 1.5SMC27CA R7G: The 23.1V reverse standoff voltage (V_RWM) is the maximum DC or peak AC voltage the TVS can sit across without conducting appreciably. On a 24V nominal rail with 5% tolerance, the rail sits at 25.2V max — above V_RWM, so the TVS will conduct leakage current at steady state. This part is better suited to a 18V or 20V rail where the operating voltage stays below 23.1V with margin. At the 42A peak pulse current (I_PP), the clamping voltage rises to 37.5V max. That 37.5V is what the downstream circuitry must survive. If the protected device has a 30V abs-max rating, this TVS will not protect it — the clamp voltage exceeds the device rating. The 1500W peak pulse power rating is the product of V_CL and I_PP at the test waveform; it is not a continuous rating. Leakage current increases with temperature, but the clamping performance is stable across the full range. The DO-214AB package's thermal resistance is set by the PCB copper area under the cathode tab — a 600mm² pad on a 2oz copper board is typical for full 1500W derating.
The R7G suffix denotes Tape & Reel packaging — 7-inch reel, 850 pieces per reel for the DO-214AB package. This is the standard reel size for automated pick-and-place assembly lines.