What the 400 W rating means on a 24 V rail
The SMAJ24A-13-F: On a 24 V nominal rail, the reverse standoff voltage is exactly 24 V — it sits across the rail without conducting until a transient pushes above 26.7 V (the minimum breakdown voltage). The junction temperature range is -55 °C to 150 °C, so it handles the thermal pulse from a 400 W surge without derating at typical ambient temperatures.
Package and board-fit: DO-214AC (SMA)
The DO-214AC (SMA) package is a standard surface-mount footprint with two terminals — cathode band on the body marks the unidirectional orientation. The supplier device package is also listed as SMA, so the land pattern matches the JEDEC standard for this outline. Available in Tape & Reel (TR) or Cut Tape (CT) for prototyping.